lfw201307-dl

www.laser focusworld.com Ju ly 2013

High-NA EUV optics are on the way PAGE 13

2D IR spectroscopy reveals molecular dynamics PAGE 39

Silicon photonics meet evolving requirements PAGE 51

3D digital holograms visualize biomedical applications PAGE 55

International Resource for Technology and Applications in the Global Photonics Industry

Smart glasses: Niche novelty or useful tool? PAGE 33

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JULY 2013 ■ VOL . 49, NO. 7

International Resource for Technology and Applications in the Global Photonics Industry

July 2013 www.laserfocusworld.com Laser Focus World 2

d e p a r t m e n t sc o l u m n s

n e w s b r e a k s w o r l d n e w s

L A S E R S ■ O P T I C S ■ D E T E C T O R S ■ I M A G I N G ■ F I B E R O P T I C S ■ I N S T R U M E N T A T I O N

Laser Focus World presents a “Full

Spectrum” view of photonics and

optoelectronics—this month, senior

editor Gail Overton speaks with

Henry Kapteyn, founder and CEO

of KMLabs, whose product won

the 2013 CLEO/Laser Focus World

Innovation Award.Click this link to view the video in your

browser: http://bcove.me/bhtf0jn0

Full Spectrum

13 EUV Lithography

High-NA EUV optics

are on their way

14 Optical Surface Inspection

Structured-light 3D scanner

speeds aircraft rivet inspection

18 Polariton Lasers

Two groups demo electrically

powered polariton lasers

21 Metamaterial Optics

Simple layered flat metamaterial

lens focuses in the UV

24 White-light Sources

Sapphire-core fiber

produces broadband

UV-visible light for OCT

9

ALD process delivers pinhole-

free, very large optics

2D refractive-index mapping

models cosmological systems

3D photonic crystal creates high-

quality warm-white LED

10

World’s fastest photodetector

has 70 GHz bandwidth

11

Optofluidic switch ducts light for

solar illumination

7 THE EDITOR’S DESK

Products from innovation

W. Conard Holton

Associate Publisher/Chief Editor

31 SOFTWARE & COMPUTING

Development of optical thin-film modeling forges ahead

Angus MacLeod

68 BUSINESS FORUM

Exploiting an unmet demand is a good model for success

Milton Chang

59 NEW PRODUCTS

66 BUSINESS RESOURCE CENTER

64 MANUFACTURERS’ PRODUCT SHOWCASE

67 ADVERTISING/WEB INDEX

67 SALES OFFICES

1307LFW_2 2 7/3/13 1:24 PM

3Laser Focus World www.laserfocusworld.com July 2013

f e a t u r e s

LFW on the Web Visit www.laserfocusworld.com for breaking news and Web-exclusive articles

33 COVER STORY

Bidirectional OLED-

based data eyeglasses

allow the user to interact

with the Internet or other

smart data using “gaze

control” or eye track-

ing for truly hands-free

operation. (Courtesy of

Fraunhofer COMEDD)

33 Photonics Applied: Displays

Head-worn displays: Useful

tool or niche novelty?

While initial responses to commercial

head-worn displays such as Google Glass

have been positive, only time will tell if

these products gain immediate traction or

follow a slow march into consumer favor

much like 3D technology. Gail Overton

39 Ultrafast Tunable Lasers

2D infrared spectroscopy

moves toward mainstream use

A unique method to investigate molecular

structure and dynamics has become a

practical research tool, thanks to the

advent of user-friendly, integrated 2D IR

spectrometers. Martin Zanni, Chris Middleton,

Marco Arrigoni, and Joseph Henrich

45 Fiber-optics Test & Measurement

Specifications guide active

and passive optical fiber

characterization

The use of optical fibers—in fiber lasers,

for example—is greatly facilitated by their

proper characterization. The resulting data

are the foundation for optimized device

designs and efficient product development.

Rüdiger Paschotta

51 Photonic Frontiers: Silicon Photonics

Silicon photonics evolve to

meet real-world requirements

The goal remains the same: integrating

photonics with electronics to cut costs

and improve data-link performance. But

developers have accepted the need for

compound semiconductor light sources,

bonded to silicon or external to the chip.

Jeff Hecht

55 Biomedical Imaging

3D digital holograms visualize

biomedical applications

Digital holograms—whether of DNA, cells,

full-sized organs, or even the life-sized

human body itself—can be holographically

printed for a range of 3D analysis

applications in the biomedical industry.

Javid Khan

Coming in

August

New RGB LED applications change the world of lighting

The first generation of solid-state lighting is finding growing applications because it offers clean and efficient illumination, but it’s little more than a replacement for existing incandescent and fluorescent lamps. A new generation is emerging based on mixing light from red, green, and blue (RGB) LEDs to generate white light that can be tuned in color by varying the relative intensities of the lamps.

1307LFW_3 3 7/3/13 1:58 PM

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www.laserfocusworld.com

5Laser Focus World www.laserfocusworld.com July 2013

laserfocusworld.online More Features, News & Products

t r e n d i n g n o wc o o l c o n t e n t

Blog: Spectral Bytes

Spectral Bytes to

stimulate your brain

Grab a “byte” with Laser Focus World

contributing editor and industry

expert Jeff Hecht on a silicon micro-

Raman laser, as well as deep-UV

LEDs that can prolong freshness

of produce. http://bit.ly/12N49Z6

Blog: Photon Focus

CLEO highlights Tech Transfer opportunities

Senior editor Gail Overton discusses the fact

that optics and photonics tradeshows are now

featuring more special sessions and programs

on technology transfer. Keep coming

back to our blog for more hot topics,

cool commentary, and other events-

related musings! http://bit.ly/14RIfUO

Webcasts let you make new

discoveries from your desktop

Whether you are looking to learn about the challenges

encountered during process scale-up of optical-grade

transparent Spinel ceramic, the latest in green lasers, or the

fundamentals in optical coating design, we’ve got webcasts

aplenty to meet your educational needs. http://bit.ly/Onhs9J

Mobile your way!

You can access the latest Laser Focus World

content on iPads, iPhones, and Android phones.

Visit our mobile app page and click on the

tabs to get news at the speed of light!

http://bit.ly/SUq2zF

Video: 2013 CLEO/Laser Focus World Innovation AwardsTAG Optics was awarded an honorable

mention in the 2013 CLEO/

Laser Focus World Innovation

Awards program for its ultrahigh-

speed TAG Lens 2.0.

http://bit.ly/14MSoBx

Focus on Fiber-opticsOptical fiber is probably best known for

communications applications, but there are many

other types and applications of fiber-optics.

Distributed fiber-optic sensor market to reach $1.1B in 2016The distributed fiber-optic sensor market is

forecast to be $586 million in

2013 and projected to be $1.1

billion in 2016, according to a

recent market survey report.

http://bit.ly/18l5BHe

Optical fiber sees growth as medical sensorsThe intrinsic physical characteristics of optical

fiber combined with its versatility

in remote sensing make it an

attractive technology for biomedical

applications. Alexis Mendez

http://bit.ly/K6TYJk

Distributed fiber-optic sensing solves real-world problemsFiber Bragg grating (FBG)-based sensing

technology originally developed by NASA

represents a 20-fold improvement over existing

sensing solutions and could

represent a quantum leap forward

for several industries. Pierrick Vuillez

http://bit.ly/TH189w

Our editors video chat with industry leaders

Get an insider’s look with video interviews, featuring

leaders in the field, as they sit down for some

tech talk with our editorial team. Contact Conard

Holton at [email protected] if you’ve got some

exciting insights to share! http://bit.ly/11i8ORN

1307LFW_5 5 7/3/13 1:24 PM

25 Gbaud QPSK Constellation

Typical QPSK Bit Error Ratio (per channel)

25 Gbaud QPSK Eye Pattern

16 QAM Constellation

1307LFW_6 6 7/3/13 1:24 PM

editor’s desk

7Laser Focus World www.laserfocusworld.com July 2013

W. Conard Holton

Associate Publisher/

Editor in Chief

[email protected]

EDITORIAL ADVISORY BOARD

Stephen G. Anderson, SPIE;

Dan Botez, University of Wisconsin-

Madison; Walter Burgess, Power

Technology; Connie Chang-Hasnain,

UC Berkeley Center for Opto-electronic

Nanostructured Semiconductor

Technologies; Pat Edsell, Avanex;

Jason Eichenholz, Open Photonics;

Thomas Giallorenzi, Naval Research

Laboratory; Ron Gibbs, Ron Gibbs

Associates; Anthony M. Johnson,

Center for Advanced Studies in

Photonics Research, University of

Maryland Baltimore County;

Kenneth Kaufmann, Hamamatsu

Corp.; Larry Marshall, Southern Cross

Venture Partners; Jan Melles,

Photonics Investments;

Masahiro Joe Nagasawa, TEM Co. Ltd.;

David Richardson, University of

Southampton; Ralph A. Rotolante,

Vicon Infrared; Samuel Sadoulet,

Edmund Optics; Toby Strite,

JDS Uniphase.

EDITORIAL OFFICES

Laser Focus World

PennWell Corporation

98 Spit Brook Road, LL-1, Nashua, NH 03062-5737

(603) 891-0123; fax (603) 891-0574

www.laserfocusworld.com

CORPORATE OFFICERS

Frank T. Lauinger Chairman

Robert F. Biolchini President and CEO

Mark Wilmoth Chief Financial Officer

TECHNOLOGY GROUP

Christine A. Shaw Senior Vice President/

Group Publishing Director

Subscription inquiries

(847) 559-7520; fax (847) 291-4816

e-mail: [email protected]

web: www.lfw-subscribe.com

Christine A. Shaw Senior Vice President & Group Publisher,

(603) 891-9178; [email protected]

W. Conard Holton Editor in Chief, (603) 891-9161; [email protected]

Gail Overton Senior Editor, (603) 305-4756; [email protected]

John Wallace Senior Editor, (603) 891-9228; [email protected]

Lee Mather Associate Editor, (603) 891-9116; [email protected]

CONTRIBUTING EDITORS

Jeffrey Bairstow In My View, [email protected]

David A. Belforte Industrial Lasers, (508) 347-9324; [email protected]

Jeff Hecht Photonic Frontiers, (617) 965-3834; [email protected]

D. Jason Palmer Europe, 44 (0)7960 363 308; [email protected]

Adrienne Adler Marketing Manager

Meg Fuschetti Art Director

Sheila Ward Production Manager

Chris Hipp Senior Illustrator

Debbie Bouley Audience Development Manager

Alison Boyer Ad Services Manager

Products from innovationThe global economic climate remained uncertain throughout the spring, resulting in attendance that was

flat or slightly down at several major photonics trade shows. Yet in each case, these conferences and

exhibitions brought out the best in terms of innovative technologies and new products. SPIE Defense,

Security + Sensing in April felt the effects of U.S. government budget struggles and sequestration, but

put on display strong advances in technologies for the infrared, unmanned vehicles, and simulation train-

ing. At LASER World of Photonics in May, the ongoing European recession could be forgotten amidst a

formidable array of industrial laser manufacturers’ booths and an additive manufacturing zone, along with

many companies focused on products for biophotonics.

CLEO in June also faced the restrictions on federal research funding, and responded with excellent

technical sessions and a rewarding series of market-oriented panels on topics ranging from opportunities

for biomedical lasers to a useful technology transfer program. The CLEO/Laser Focus World Innova-

tion Awards honored Femtolasers Produktions, Princeton Instruments, and TAG Optics, as well as winner

KMLabs, which Milton Chang interviews in a new format of his Business Forum column (see page 68).

The potential commercial impact of innovative photonics products is readily apparent in our cover story

on “smart glasses,” also known as head-worn displays or, in one well-publicized manifestation, Google

Glass (see page 33). Smart glasses may have major societal impacts, but so do or will many of the other

technologies explored in this issue, from optical fiber (see page 45) to silicon photonics (see page 51), and

from 2D infrared spectroscopy (see page 39) to 3D biomedical digital holograms (see page 55). Indeed,

the local forecast for photonics innovation is for a fair wind with many new products expects.

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9Laser Focus World www.laserfocusworld.com July 2013

newsbreaks

3D photonic crystal creates

high-quality warm-white LED

Standard white-light LEDs are made by layering a yel-

low-emitting cerium-doped yttrium-aluminum-gar-

net (YAG:Ce) phosphor over a blue-emitting gallium ni-

tride (GaN)-based emitter; the combination of blue and

broadband yellow approximates white light for many

purposes. For indoor lighting, many people prefer a

warm-white light; to achieve this, the proportion of light

emitted by the YAG:Ce phosphor is increased. The result,

however, is often light with a low color

Wavelength (nm)

Output intensity (a.u.)

650 700

10

12

8

6

4

2

0

600550500450400 800750

c-WLEDs

c-WLEDs with NCP CPhCs of a = 349 nm

c-WLEDs with NCP CPhCs of a = 385 nm

w-WLEDs

2D refractive-index mapping

models cosmological systems

Researchers at King Abdullah University of Science and Tech-

nology (Thuwal, Saudi Arabia) and King Fahd University of Pe-

troleum and Minerals (Dhahran, Saudi Arabia) are looking at

planar (2D) optical refractive-index distributions that, if creat-

ed using a metamaterial, could become an experimental way

of creating many observable analogies to celestial mechanics

such as gravitational attractors. For example, in a stationary,

planar, rotationally symmetric index mapping, light could “or-

bit” the center. Depending on the index distribution, incoming

light could be captured by the device as a cosmological black

hole would.

The refractive index falls within the range of 0.8 to 3.5

(making metamaterials the primary way of experimental re-

alization). In addition to a rotationally symmetric version, a

mapping with two lobes can mimic a cosmological binary sys-

tem. Practical uses for the concept also exist: because the

light paths are very sensitive to the refractive-index distribu-

tion, a sensor could be created that would take advantage of

very small changes in refractive index (for example, resulting

from changes in temperature or chemical concentration). The

researchers propose numerous other applications, including

as transient optical memories of an optical delay, a light con-

centrator, a chaotic cavity, and a beam homogenizer. Contact

Boon S. Ooi at [email protected].

ALD process delivers pinhole-free, very large opticsIn addition to its ion-beam-sputtering

(IBS) deposition process that can uni-

formly coat half-meter optics, MLD Tech-

nologies has scaled up its atomic-lay-

er-deposition (ALD) process to provide

uniform (less than ±1% variation), low-

loss (typically less than 50 ppm total loss)

precision optical coatings on substrates

up to 800 mm in diameter.

The ALD process creates pinhole-free

coatings one monolayer at a time from

the chemical reaction of gas-phase pre-

cursors for excellent barrier properties for

wet or corrosive chemical environments.

Coating designs for the near-ultravio-

let to mid-infrared wavelength region

can be deposited from a number of met-

al-oxide film materials. The production-

scale ALD chamber designed and built

by MLD is capable of coating planar, 3D,

and large curved optical elements. A pi-

lot-scale chamber is also available to coat

substrates smaller than 250 mm diameter

and for process development. MLD can

also produce hybrid coatings, comprised

of IBS layers in combination with ALD

layers. These hybrid coatings are critical,

for example, when fabricating high-ener-

gy laser mirrors or other optics exposed

to harsh chemical or corrosive environ-

ments. Contact Ric Shimshock at

[email protected].

continued on page 10

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quality, sometimes even looking greenish.

Correcting this problem usually means

adding some expensive red-emitting

phosphor to the mix. Even then, warm-

light LEDs (w-WLEDs) have lower effi-

ciency than cool-white LEDs (c-WLEDs).

Researchers at Feng Chia Universi-

ty (Taichung, Taiwan) and Academia Si-

nica (Taipei, Taiwan) have come up with

another approach for improving color

quality: layering a 3D non-close-packed

(NCP) colloidal photonic crystal (CPhC)

with a unit-cell size (a) of 349 to 385 nm

over the yellow phosphor. The stopbands

in the CPhC improve both the color quali-

ty (quantified as the color-rendering index

or CRI) and the closeness to a blackbody

emission (quantified as the correlated col-

or temperature, or CCT). And, because

the researchers start by layering the CPhC

on top of a more-efficient c-WLED, with

the CPhC hardly affecting the efficiency

of the resultant light output, the result is a

more efficient w-WLED source. Contact

Chun-Feng Lai at [email protected].

3D photonic crystal continued from page 9

World’s fastest photodetector has 70 GHz bandwidth

Designed to support next-generation op-

tical communications networks using 400

Gbit/s or 1 Tbit/s coherent detection-

based optical transmission, u2t Photonics

(Berlin, Germany) has developed what it

says is the world’s fastest balanced photo-

detector, with a bandwidth of 70 GHz.

The optical front end of the BPD-

V3120R photodetector consists of a

monolithically integrated balanced pho-

todetector chip using waveguide-based

indium phosphide (InP) technology to

enable extremely high bandwidth. They

are integrated onto a single InP chip and

optimized to produce guaranteed linear

frequency response, even at very high

power levels. The coaxial single-ended

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linearity, and optical input power speci-

fications for error-free operation in long-

haul transmission systems at data rates

of 400 Gbit/s and beyond. It can also

be used in telecommunications test and

measurement equipment. Contact Jens

Fiedler at [email protected].

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newsbreaks

Optofluidic switch ducts light for solar illumination

Solar interior lighting can be very low-

tech, as in a window, or high-tech, as

in light collected by roof-based op-

tics and ducted into and around rooms.

One way of doing the lat-

ter is to focus light via a con-

centrator into an optical fiber,

which can be a very adapt-

able way to route light with-

in buildings. However, one

thing this type of system

needs is a device to configu-

rably switch the light stream

from a fiber into a room.

Mechanical switches with

flipping mirrors and addi-

tional optics are possible, but are large,

costly, and ultimately unreliable.

A simple optofluidic alternative has

been created by Wuzhou Song and

Demetri Psaltis of the Swiss Federal

Institute of Technology Lausanne (Lau-

sanne, Switzerland), which is based on

a waveguide that has a thin oil film and

closely spaced interdigitated electrodes

on one side. When there is no voltage

drop across the electrodes, the oil film

has a uniform thickness and the light

passes through the waveguide. When

a voltage is applied, the oil bunches up

between the electrodes due to electro-

phoretic effects and creates a leaking

(not a diffraction) grating, ducting light

that is zigzagging in the waveguide out

the side. With a film of 18 to

24 µm of silicone oil and an

electrode period of 200 µm,

a 50-mm-long waveguide

with a cross-section of

535 µm × 4 mm (with light

coupled in and out via fi-

ber bundles), the light is

switched one way or the

other by switching on and

off a voltage of 800 V. On

and off response times wer-

e 0.15 and 5 s, respectively; the latter

time was shortened to 0.3 s if the elec-

trodes were short-circuited to eliminate

capacitance effects. Contact Wuzhou

Song at [email protected].

Grating off

Grating on

1307LFW_11 11 7/3/13 1:25 PM

© Copyright OptoSigma, 2013. All rights reserved.

Optical Thin Film CoatingsCustom, Catalog and OEM

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1307LFW_12 12 7/3/13 1:25 PM

world newsTechnical advances from around the globe

13Laser Focus World www.laserfocusworld.com July 2013

Got News? Please send articles to [email protected]

Flat UV

lens

See page 21

E U V L I T H O G R A P H Y

High-NA EUV optics are on their wayBy taking advantage of techniques such as 193 nm water-immer-

sion optics, semiconductor photolithography has enabled shrink-

ing of feature sizes on computer chips to around 22 nm. But

wiggle room for traditional glass-based transmissive lithographic

optics has shrunk; moving below 20 nm or so will require shorter

wavelengths. With the development of 13.5 nm extreme-ultra-

violet (EUV) light sources by Cymer (San Diego, CA) and others,

as well as optics such as the NXE:3300 platform by ASML (Veld-

hoven, The Netherlands) with a numerical aperture (NA) of 0.33,

EUV appears to be progressing toward practical use.

But—as with any optical system—the higher the NA, the

better the potential resolution. As a result, SEMATECH (SEmi-

conductor MAnufacturing TECHnology Association) and the

College of Nanoscale Science and Engineering at the State Uni-

versity of New York (both in Albany, NY), have a program to

develop small-field EUV exposure tools with NAs of 0.5.

Recently, a team of researchers from Zygo Corporation’s

Extreme Precision Optics (EPO) division (Richmond, CA),

SEMATECH, Lawrence Berkeley National Laboratory

(LBNL; Berkeley, CA), Hyperion Development (San

Ramon, CA), and Lawrence Livermore National Labo-

ratory (LLNL) and Spiller X-ray Optics (both in Liver-

more, CA) presented results of their efforts to produce

and make a 0.5 NA EUV optical projection module.1

Modified Schwarzschild design

The design of the 5X-reduction projection optics, which are

made of a material with a near-zero coefficient of thermal

expansion, is based on a Schwarzschild design modified so that

the mirrors are 16th-order aspheres with separated centers of

curvature, as opposed to the standard Schwarzschild configura-

tion with two concentric spheres. The field is small (20 × 300

µm) but is sufficient for research into EUV photoresists, photo-

mask materials, and so on; the feature-size (half-pitch) resolution

is 11 nm, and with certain illumination approaches such as

extreme dipole illumination, can be as good as 8 nm. In addition,

the optical system size (as well as the reduction ratio, mass, and

other parameters) is constrained by a requirement that it fit into

an existing research tool as an upgrade to the previous optics.

To achieve these results, the transmitted wavefront error of

the two-mirror optical projection module is specified to be less

than a 1 nm root-mean-square (RMS) over the entire image

field. Zygo Corporation, which has two decades of experience

in fabricating EUV optics and has previously supplied optics

for EUV systems, is responsible for the modified-Schwarzschild

mirror fabrication and metrology.

The large amount of asphericity in the new EUV mirrors leads to

higher-frequency spatial periods than in previous designs, making

polishing more difficult and necessitating more steps in the fabrica-

tion process. When added to the tight surface tolerances, fabrica-

tors and metrologists have their work cut out for them.

Fabrication and metrology

Zygo uses a high-precision five-axis milling machine with ultra-

sonic capabilities that boosted the material removal rate by a

factor of up to four while reducing subsurface damage. The

milling machine’s series of diamond tools lead to a ready-to-

polish surface. Polishing is done using a

subaperture computer-controlled

optical surfacing technology devel-

oped at Zygo EPO, along with

ion-beam figuring.

Monitoring of the process is

done with coordinate-measuring

machines, profilers, and interfer-

ometers; in a vertical cavity test, the

interferometer uses a Zygo-fabricated

computer-generated hologram as a dif-

fractive null element in a vertical cavity

test that imitates the as-used orientation

of the mirror optics.

Minimizing both mid-spatial frequen-

cies and microroughness is extremely

important at EUV wavelengths. Zygo

EPO designed a “sub-aperture surface

height interferometric measuring instru-

ment” (SASHIMI) with custom optics

to match the tested asphere mirrors;

the white-light instrument generates

hundreds of subapertures that were then

stitched together by software. Rough-

ness at even higher spatial frequencies

In a computer-

generated image, two

aspherical EUV mirrors

(shown in light blue) in a

modified Schwarzschild

configuration are

shown mounted in

their optomechanical

structure. A hexapod

actuator configuration

controls the positions

of the mirrors relative to

each other. (Courtesy of

Zygo Corporation)

1307LFW_13 13 7/3/13 1:25 PM

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July 2013 www.laserfocusworld.com Laser Focus World 14

between 10 µm and 10 nm is character-

ized by an atomic-force microscope.

The period of the multilayer high-

reflection coatings deposited on the

mirrors is varied across the clear apertures

to maximize reflectivity at the local angles

of incidence; the molybdenum/silicon

coating was developed at LLNL and is

deposited using magnetron sputtering.

The optomechanical structure for the

two mirrors is made from Super-Invar,

which has a low CTE. The mirrors are

mounted via bipod structures with inte-

grated flexures (see figure); the relative

orientation of and distance between the

two mirrors are controlled using an actu-

ator-driven hexapod structure.

Alignment of the optics and wave-

front measurement is done via interfer-

ometer at a 633 nm wavelength to 0.5

nm RMS at the center of the field and

1.0 nm RMS at the edge of the field. Dis-

placement sensitivities for the testing are

high: for example, a 13 nm image-plane

displacement produces 0.5 nm RMS of

defocus error (which is easily tweaked

out, but gives an idea of the other align-

ment sensitivities).

Performance of the system was com-

puter-modeled; analysis included printing

of 12 nm lines and spaces using annular

illumination with a pupil fill of 0.93 and

a donut-hole size of 0.36 of the pupil.

Results showed an acceptable critical-

dimension variation of ±10%. A simu-

lation of printing 8 nm lines and spaces

with extreme dipole illumination showed

a depth of focus greater than 100 nm for

a ±10% change.

The annular illumination configuration

will be available on systems being created

for the Albany and LBNL sites, while the

extreme-dipole configuration is intended

for the LBNL system. —John Wallace

REFERENCE

1. H. Glatzel et al., Proc. SPIE Advanced Litho-

graphy, 8679-42 (2013).

O P T I C A L S U R F A C E

I N S P E C T I O N

Structured-light 3D scanner speeds aircraft rivet inspectionA typical commercial aircraft is held

together by several hundreds of thou-

sands of rivets—or “fasteners,” as they

are called in aerospace industry jargon—

that can result in significant safety and

fuel-efficiency issues if improperly installed.

Ensuring proper fastener insertion while

maintaining high levels of manufacturing

efficiency has been a constant balancing

act when using traditional inspection tech-

niques. Recent innovations in structured-

light 3D optical scanning and augmented

reality (AR) techniques from 8tree (Denver,

CO and Daisendorf, Germany)—the

2013 SPIE Startup Challenge winner—are

making it possible to achieve both proper

fastener insertion and efficiency.1

How it works

fastCHECK is an application-spe-

cific, 3D-structured light scanner opti-

mized to measure fastener flushness with

high speed and accuracy and consis-

tent repeatability. The system consists of

a solid-state, WVGA-resolution, MEMS-

based light engine and a VGA-resolution,

125 frame/s CCD sensor coupled with

supporting electronics and proprietary

measurement and analysis software.

The light engine projects structured

light patterns (variable-width fringes) onto

the target aircraft surface and the reflec-

tions are detected by the sensor. Using

well-established triangulation techniques,

8tree’s software performs a combination

of 2D imaging to detect the exact physical

location of a fastener combined with 3D

image analysis of the reflected image to

determine depth of the fasteners on the

aircraft surface with a scan-acquisition

time of approximately 100 ms. Operators

can perform a one-time parameter adjust-

ment specific to their task that will impact

measurement results, such as fastener

1307LFW_14 14 7/3/13 1:25 PM

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July 2013 www.laserfocusworld.com Laser Focus World 16

diameter and tolerances. After the few

seconds required to set these parameters,

the operator’s involvement is simplified to

pushing a single button.

Integrated into the system is a pat-

ent-pending AR technique that projects

the analyzed results of the scan back

onto the target surface in the form of

color codes and detailed dimensional and

angular data annotations (see figure). This

real-time AR technique eliminates the

standard and repetitive process of looking

up scan data on a computer terminal and

interpreting it “offline” and instead allows

users to perform “inline” measurements.

By abstracting the complex and time-

consuming task of interpreting 3D scan

data away from the operator and over-

laying color-coded “pass-fail” images

directly on the scanned surface, the

system significantly boosts manufactur-

ing and inspection efficiency. The light

engine serves double duty by first pro-

jecting fringe patterns to enable scanning

and then subsequently displaying the

measurement results to create the AR

image on the surface of the aircraft.

Early industry benchmarking shows that

fastCHECK can scan, analyze, and deliver

actionable information at a rate of greater

than 1 fastener/second with repeatability

and reproducibility (R&R) that sits below

the 10% threshold of analysis of variance

(ANOVA) gauge R&R measurement

system analysis studies while maintaining

25 µm accuracy and 5 µm resolution for

an 18 × 24 cm field of view. The total time

for scan, measurement analysis, and visual

overlay of results is less than two seconds.

In-process inspection

Fastener-flushness inspection is usually

completed after fastener insertion and

typically as part of the quality assurance

phase of the workflow. But fastCHECK

combines scanning, analysis and AR visu-

alization with the potential for real-time

inspection and on-the-spot rework.

“Against the backdrop of manual tactile

inspection methods that require opera-

tors to remain actively ‘hands-on’ at all

times, the industry has gained a great

deal with the adoption of optical scanning

systems, which have reduced a user’s

active involvement during measurement

to dozens of mouse-clicks,” says 8tree

cofounder Arun Chhabra. “Taking this a

step further, by pursuing a highly targeted

application focus and incorporating AR

techniques using fastCHECK, the user-

interaction can be reduced further to a sin-

gle-button-push. And our next-generation

system aims to build on current perfor-

mance by incorporating gesture recogni-

tion, thereby simplifying the user-experi-

ence to a natural ‘no-click’ environment.”

Chhabra says 8tree’s fastCHECK

product is currently undergoing exten-

sive evaluation by the aerospace

industry and is scheduled to be intro-

duced in the manufacturing workflow

soon. —Gail Overton

REFERENCE

1. See http://spie.org/x88933.xml.

Aircraft rivets or fasteners

are subject to numerous

installation errors and

require detailed optical

inspection (a). The

fastCHECK system

uses 3D structured light

to analyze installation

parameters and compare

against pass/fail criteria (b).

1307LFW_16 16 7/3/13 1:25 PM

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July 2013 www.laserfocusworld.com Laser Focus World 18

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P O L A R I T O N L A S E R S

Two groups demo electrically powered polariton lasers

A new type of low-power semiconduc-

tor laser has reached an important mile-

stone—the first electrically powered

operation. Two independent groups

described strikingly similar demonstra-

tions in reports published within hours of

each other on May 15, 2013, in Nature

and Physical Review Letters.1, 2 Neither

group knew about the other’s success

until they saw the papers.

Atac Imamoglu of the Swiss Federal

Institute of Technology (Zurich, Swit-

zerland) in 1996 proposed the concept

of extracting coherent, monochro-

matic light from polaritons, which are

quasiparticles formed by the interac-

tion between a photon and an elec-

tron-hole pair (exciton) in a semicon-

ductor. Polaritons are bosons, so many

of them can occupy the same quantum

state, creating a condensate similar to a

Bose-Einstein condensate. Polaritons in

these states have subnanosecond life-

times, spontaneously decaying by releas-

ing a photon. Because all polaritons in a

condensate occupy the same quantum

state, the emitted photons are coherent

and monochromatic.

Potentially very efficient

Theory predicts high polariton-laser effi-

ciency at low powers, making them

attractive for applications such as optical

interconnects. The polariton mecha-

nism does not require a population inver-

sion, says Alexey Kavokin of the Uni-

versity of Southampton (Southampton,

England). “That is why we expect thresh-

olds maybe orders of magnitude lower”

than conventional semiconductor micro-

lasers, he notes. Polaritons also promise

very high speed. It took just two years

for the first polariton laser to be demon-

strated by optical pumping of a cryogen-

ically cooled semiconductor microcavity.

Kavokin’s group was the first to demon-

strate optical pumping at room tem-perature in 2007.3

Shifting to electrical pumping required

major changes, starting with doping the

microstructure to produce

a p-n junction and conduct

current. The logical semi-

conductor for experiments

was gallium arsenide (GaAs)

because its technology is well

developed, and light emission

in a polariton light-emitting

diode was developed in 2008.4

But developing a device that

produced coherent, mono-

chromatic laser light—and

produced persuasive evidence

that the light came from

polaritons rather than from the

laser-like microcavity—took

considerably longer.

One key issue was the

nature of the polariton excita-

tion and condensation process.

“It starts with creating an

electron-hole plasma which

An electrically pumped polariton laser is shown in

a schematic cross-section. The structure, which

consists of a 20-µm-diameter micropillar with a gold

ring electrode on top, has an active layer sandwiched

by distributed Bragg reflectors (DBRs). The active layer

contains four InGaAs quantum wells.

1307LFW_18 18 7/3/13 1:25 PM

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world news

July 2013 www.laserfocusworld.com Laser Focus World 20

generates a population of excitons, and

these excitons then couple with photons

in a resonant cavity to produce polari-

tons,” says Pallab Bhattacharya of the

University of Michigan (Ann Arbor, MI),

whose group described its approach in

Physical Review Letters. However, a bot-

tleneck can occur in scattering the polari-

tons to the lowest polariton energy

levels, blocking production of the large

coherent population of polaritons at

the levels needed for coherent emission.

Both groups overcame that problem

by applying strong magnetic fields of

several Tesla, increasing the scattering to

overcome the bottleneck and help them

demonstrate polariton-laser action.

Cooling was required

Bhattacharya says another issue is that

in GaAs the exciton binding energy is

relatively weak, so the excitons tend

to fall apart well below room tempera-

ture, preventing polariton emission. That

was solved by cooling the GaAs micro-

cavities to temperatures of 10 to 30 K.

Low temperatures showed the physics

clearly, says Sven Höfling of the Univer-

sity of Würtzburg (Würtzburg, Germany),

whose group reported its approach in

Nature. Operating at higher tempera-

tures will require semiconductors with

wider bandgaps, such as nitride or II-VI

compounds.

Proving that experiments actually

demonstrated polariton lasing was

a challenge because the microcavity

diode strongly resembles a VCSEL, with

a resonant cavity that could produce

laserlike effects. Höfling says his group

needed more than two years to convince

referees that they were observing nonlin-

ear emission from the polariton process,

rather than a weakly coupled micro-

cavity laser. “We saw all the signatures

[of polaritons] without the magnetic

field,” he says, but they had to add the

magnetic field to make the observations

definitive. Bhattacharya recalls some

sleepless nights worrying if his group’s

evidence was definitive. The simultane-

ous publication of independent results

was an additional confirmation.

Some quibbling over definitions is

still likely because, strictly speaking, the

coherent output photons are produced

by spontaneous emission from the

coherent polariton states. Bhattacha-

rya calls the process “light amplification

by stimulated scattering of polaritons

[LASSPs],” but it remains to be seen if

polariton lasers will become LASSPs.

Both groups say their next steps

will be trying to demonstrate electri-

cal pumping at the higher tempera-

tures needed for practical applications,

with room temperature the ultimate

target. That will require switching to

wide-bandgap semiconductors such as

gallium nitride or zinc oxide. Success

would open the way for polariton use in

applications where low power consump-

tion is critical, such as optical intercon-

nects, switches, and logic gates. Kavokin

suggests polaritons might also generate

terahertz frequencies. And Höfling is

hoping that electrical excitation at room

temperature also can generate polariton

condensates—analogs of Bose-Einstein

condensates that would be much easier

to produce and use. —Jeff Hecht

REFERENCES

1. C. Schneider et al., Nature, 497, 348 (May 16,

2013); doi:10.1038/nature12036.

2. P. Bhattacharya et al., Phys. Rev. Lett., 110,

206403 (2013); doi: 10.1103/PhysRev-

Lett.110.206403.

3. S. Christopoulos et al., Phys. Rev. Lett., 98,

126405 (2007).

4. S. I. Tsintzos et al., Nature, 453, 372 (May 15,

2008); doi:10.1038/nature06979.

Theory predicts high

polariton-laser efficiency

at low powers, making

them attractive for

applications such as

optical interconnects.

1307LFW_20 20 7/3/13 1:25 PM

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M E T A M A T E R I A L O P T I C S

Simple layered flat metamaterial lens focuses in the UV

A team of U.S. and Canadian scien-

tists has created an easily fabricated

sputtered-on flat thin-film metamate-

rial lens that works at UV wavelengths.1

The team includes scientists from the

National Institute of Standards and Tech-

nology (NIST; Gaithersburg, MD), the

University of Maryland (College Park,

MD), Syracuse University (Syracuse, NY),

and the University of British Columbia

(Kelowna, BC, Canada).

The lens consists of alternating layers of

metal and dielectric—in this case, silver

(Ag) and titanium dioxide (TiO2) on the

order of 30 nm thick—on a transpar-

ent glass substrate. The structure forms

many strongly coupled plasmonic sheet

waveguides that allow a transverse-mag-

netic-polarized (TMP) backwards elec-

tromagnetic mode with a frequency that

falls between the bulk plasmon-reso-

nance frequency of the metal and the

surface plasmon-resonance frequency of

the metal-dielectric interface; in this case,

the researchers chose to work with light

at 363.8 nm.

One-to-one 3D imaging

Because the metamaterial has a refrac-

tive index of -1, the incidence angle (with

respect to the surface normal) of any ray

passing into or out of it is flipped (multi-

plied by -1). The result is an unusual sort

of image in which light from every point

on one side of the lens is focused to a

corresponding point on the other side of

the lens that is exactly the same distance

away from the lens, and also has the

same lateral position; so, for example, an

object point at (x, y, z) gets imaged to (x,

y, -z). The result is a 3D mirror image of

the object, always at unity magnification

and without lens aberrations. Also, as a

result, the lens has no optical axis and

could in theory be made into an arbi-

trarily large sheet and still create images

of the same high quality.

While the distances between the lens—

which is only 450 nm thick—and the

object and image are small (on the order

of the lens thickness), the lens is a far-field

imager, meaning that an image appears in

free space, rather than on the lens surface.

On the metamaterial lens, which has

both negative electric permittivity and negative magnetic permeabil-ity, the researchers deposited an opaque

film of chromium (Cr) in which was pat-

terned a 600-nm-wide illumination

aperture. Through this aperture, they

1307LFW_21 21 7/3/13 1:25 PM

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a)

b)

world news

July 2013 www.laserfocusworld.com Laser Focus World 22

confirmed negative refraction for

TMP light, along with conven-

tional—and expected—positive

refraction for transverse electric

polarization.

Because linearly polarized light

thus results in focusing only in one

direction, the researchers actually

use circularly polarized light for

imaging experiments; light with

a circular polarization has equal

amounts of the two orthogonal

linear polarizations (with a relative

phase shift), so that, no matter

what the orientation of the image

feature, there is always some

light available with the properly

oriented polarization.

Imaging results

Finite-difference time-domain (FDTD)

simulations for an ideal case showed

a minimum beam width at focus of

about 200 nm. However, a realistic

amount of loss, dispersion, and other

factors would be expected to degrade

this. As an experiment, the research-

ers used a UV microscope objective to

view an image created by the

metamaterial lens of a 180-nm-

wide slit (see figure). The result

showed a minimum slit width of

about 370 nm full width at half

maximum (FWHM).

The NIST researchers and

their colleagues took their

inspiration from a theoretical

metamaterial design recently

proposed by a group at the

FOM Institute for Atomic and

Molecular Physics (Amsterdam,

The Netherlands), adapting the

design to work in the UV.

According to NIST research-

ers Ting Xu, Amit Agrawal, and

Henri Lezec, aside from achiev-

ing record-short wavelengths,

the metamaterial lens is inher-

ently easy to fabricate. It doesn’t rely

on nanoscale patterns, but instead is

a simple sandwich of thin films, the

construction of which is routine. And

Two-dimensional objects such as a cross and a circle (a) with

180 nm linewidths were imaged by a metamaterial lens focusing

UV light, producing good-quality images (b). (Courtesy of NIST)

1307LFW_22 22 7/3/13 1:26 PM

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W H I T E - L I G H T S O U R C E S

Sapphire-core fiber produces broadband UV-visible light for OCT

A team of Taiwanese researchers has

developed a very broadband (near-UV

through the visible region) optical-fiber-

based light source for uses in the bio-

science and medical fields.1 Based on a

glass-clad crystalline-sapphire fiber pumped by a near-UV laser, the source

is potentially useful for optical coher-

ence tomography (OCT), as well as

fluorescence microscopy and flow

cytometry.

The group, which includes research-

ers from National Dong Hwa Univer-

sity (Hualien), National Taiwan University

(Taipei), and National Sun Yat-Sen Uni-

versity (Kaohsiung) demonstrated a fiber

with a 1.16 mW optical output power

(when pumped by a 325-nm-emitting

helium-cadmium laser) at a 4.7% opti-

cal-to-optical efficiency and a white-light

output with CIR chromaticity coordinates

of (0.287, 0.333), which is a slightly blue-

green shade of white.

Glass-clad sapphire

To fabricate the fiber, a 40-µm-diameter

sapphire single-crystalline core was

grown via a laser-heated pedestal growth

(LHPG) technique in which a carbon

dioxide (CO2) laser heats a large-diam-

eter source rod, creating a molten zone

from which a slightly hexagonal crys-

talline core is drawn. To create the color

centers (oxygen-atom vacancies) and

other spectral peaks in the sapphire

on which the white-light generation

because its design consists of a stack of

strongly coupled waveguides sustain-

ing backward waves, the metamate-

rial exhibits a negative index of refrac-

tion to incoming light regardless of its

incidence angle.

The metamaterial flat lens achieves

its refractive action over a distance of

about two wavelengths of UV light,

making possible small image distances

that are challenging to achieve with

conventional refractive optics such as

glass lenses. In addition, the researchers

determined that transmission through

the metamaterial can be turned on

and off using higher-frequency (290

nm) light as a switch, allowing the flat

lens to act as a shutter with a 50%

intensity-modulation contrast (and no

moving parts). —John Wallace

REFERENCE

1. T. Xu et al., Nature, 497, 470, doi:10.1038/

nature12158 (May 23, 2013).

1307LFW_24 24 7/3/13 1:26 PM

Wavelength (nm)

PL intensity (a.u.)

650

10,000

8000

6000

4000

2000

0600550500450400350

F+

F2+

F22+

Ti4+

F

300

Ti4+-VAl

Al×Al /F2

Ti3+

Cr3+

White light

Fitted curve

Gaussian ft peaks

Gaussian ft peaks

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25Laser Focus World www.laserfocusworld.com July 2013

depends, a small amount of titanium (Ti) and chromium (Cr)

ions were added to the core.

The core was then inserted into a borosilicate glass tube with

a 320 µm outer diameter and an inner diameter slightly greater

than the sapphire core; the same CO2 laser setup was used to

melt the glass and collapse it onto the core in a vacuum envi-

ronment; this step also caused the sapphire to be regrown. An

18-mm-long segment of the fiber was used for white-light

generation.

The fiber segment was wrapped in a tin-lead alloy and

clamped in an aluminum heat sink. Up to 25 mW of laser light

was focused by a 40X objective lens into the input end of the

fiber to generate white light. The resulting output spectrum

ranged from 300 nm out to past 650 nm (see figure).

Many possible photoluminescent (PL) bands can contrib-

ute to such a spectrum, including PL bands with peaks at 375,

420, 458, 485, 531, 577, and 648 nm that correspond to color

centers, and bands associated either with Ti or Cr and which

have peaks at 380, 420, 460, 480, 510, 590, and 650 nm. To

determine which peaks actually contributed to the actual output,

the researchers fitted a curve to the white-light spectrum, then,

assuming Gaussian profiles for all the possible PL bands, did

a best fit of the possible peaks to the overall curve. The result

revealed a combination of color centers and effects of Ti and Cr

ions, as well as aluminum vacancies filled by Ti.

The resulting high 4.7% conversion efficiency is the

highest among existing active-waveguide white-light-pro-

ducing approaches, including supercontinuum lasers, the

researchers note. —John Wallace

REFERENCE

1. C.-C.Lai et al., Opt. Exp., 21, 12, 14606 (June 17, 2013).

The broadband UV-visible photoluminescent output of a glass-

clad sapphire-core optical fiber excited by light at 325 nm includes

many components, such as peaks resulting from color centers

and Ti and Cr impurities. The 1.16 mW output and 4.7% optical-

to-optical conversion efficiency of the fiber light source make it

suitable for OCT and other biomedical applications.

1307LFW_25 25 7/3/13 1:26 PM

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(kW/cm2)LDT Testing Parameters

Product Blocking Passing �

Pulse

Duration

Rep Rate

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Exposure

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SIR7-15 110 10 ������� CW 360 30 sec.

SIR3-5 0.646 >14 ������ 7 ns 25 150 20 min.

PPL04A >538 350 1540 nm CW 33.2 60 sec.

PPL04A 17 27 1319 nm CW 62 20 min.

PPL04A 7 18 1064 nm CW 314 20 min.

PBF02C* 17.7 16.3 455 nm CW 126 x 42 20 min.

PBF02C 9 11 532 nm CW 36.08 20 min.

Disclaimer: ������������ ����������������������������������������� �� ����� ���������������������������������������������������

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1307LFW_26 26 7/3/13 1:26 PM

10-2

100

10-4

10-6

10-8

10-10

400 500 600 700

Extinction ratio

Wavelength (nm)

4° cone performance

Collimated light

Software&Computing

27Laser Focus World www.laserfocusworld.com July 2013

Development of optical thin-film modeling forges ahead

A N G U S M A C L E O D

We use models in virtually every-

thing we do, and the design and analy-

sis of optical coatings is no exception.

Here, a model is an absolute necessity

and, when implemented on a computer,

it removes from our shoulders a huge

and debilitating volume of tedious cal-

culation. The basic model, created by

Romanian-born French researcher

Florin Abelès (who also founded the

journal Optics Communications in

1969), is so good that it has remained

virtually unchanged for more than

60 years. Advanced, powerful com-

mercial programs are readily avail-

able, and it is becoming rare to find

companies that still use home-brewed

programs. In spite of the longevity of

the model, these computer programs

continue constantly to develop and ad-

vance. How can this be?

The starting model is an ideal one that assumes ideal conditions. It employs

parallel-sided films of precise thickness, featureless interfaces, and known opti-

cal constants that are illuminated by a monochromatic, linearly polarized plane

wave. Usually, our coating design—at least in the first instance—is achieved un-

der such conditions. But in the real world, illumination is never strictly mono-

chromatic nor a perfectly collimated wave of infinite extent. The coating lay-

ers have rough surfaces and their thicknesses may not be uniform. And there

may be other departures from the ideal model.

Examination of such effects requires elaboration of our model and suitable

tools for this are important components of modern thin-film software, and, re-

sponsive to the ever-growing needs of modern optics, more are constantly un-

der development. Let’s look at just two of the consequences of real-world con-

ditions where such software tools are invaluable.

Cones of illumination

Calculations at oblique incidence are a bit more complicated than those at nor-

mal incidence because of polarization effects. We decompose the polarization

of the light into two modes, one with electric field parallel to the plane of in-

cidence, p-polarization, and one with the electric field perpendicular to the

plane of incidence, s-polarization. The appropriate coating properties differ, but

these two modes possess the advantage of retaining their polarization orienta-

tion both in transmission and in reflection. Any ray at

oblique incidence, therefore, is first decomposed into its

p- and s-components that are calculated separately and

then, after emerging from the coating, are recombined

to give the resultant.

There are three effects of tilted illumination, all of

which are dependent on the cosine of the angle of prop-

agation. The interference path differences are reduced,

making the layers appear thinner, so that there is a shift

to shorter wavelengths. The performance for s-polariza-

tion tends to strengthen, while that for p-polarization

weakens; a difference in the two performance character-

istics known as polarization splitting is the result. Low-

index layers are affected more than the high, and so there

is also sometimes a further distortion of the characteris-

tic. The effects increase roughly as the square of the an-

gle as we slide down the cosine curve.

Making our optical system capable of a reasonably

FIGURE 1. Polarizer performance in collimated light shows an

extinction ratio as low as 0.000000001; however, in a 4° cone (semi-

apex angle), it reaches 0.0012—almost exactly as predicted by the

approximate expression.

1307LFW_27 27 7/3/13 1:26 PM

Wavefront error (waves)

‐0.10

‐0.08

‐0.06

‐0.04

‐0.02

0.00

‐10 ‐5 0 5 10 15

Position (mm)

Geometrical

Actual at

550 nm

Software&Computing

July 2013 www.laserfocusworld.com Laser Focus World 28

high-energy throughput results in a de-

parture from perfect collimation of the

light, and we can think of the illumina-

tion as encompassing a range of angles of

incidence. A useful model of such illumi-

nation is a cone with uniform irradiance

throughout the cone. Cones of illumina-

tion decrease edge sharpness, broaden the

spectral output of narrowband filters and,

even if nominally at normal incidence,

shift coating characteristics

slightly to shorter wavelengths.

However, there is a major

effect when thin-film polariz-

ers are involved that may not

be as well known as it should.

A common thin-film polariz-

er is a reflecting structure of

quarterwaves tilted at 45° in a

high-index glass cube. Ideally,

the p-performance is so weak-

ened that it is transmitted with-

out loss while the strengthened

s-polarization performance

results in its total reflection.

Incredibly low extinction ra-

tios (undesired or desired) can

be achieved. Problems appear,

however, as soon as we intro-

duce our cone of illumination.

The desired polarizations in such a de-

vice are locked to the principal plane of

incidence of the cone, while the actual

polarization modes of any individual ray

are locked to its local plane of incidence;

for skew rays out of the principal plane

of incidence, these are not the same. The

result is polarization leakage that lim-

its the performance of the device. It is

a geometrical effect that depends purely

on the principal angle of incidence ϕ and

the cone semi-apex angle, Φ (both mea-

sured at the coating); the limiting extinc-

tion ratio that cannot be exceeded is giv-

en to a good approximation by Φ2/(4tan2

ϕ) with Φ in radians.1

Figure 1 shows a comparison between

an ideal polarizer performance at 45° in-

cidence in collimated light and in a 4°

cone of illumination. The degraded per-

formance in the cone is virtually that

predicted by the formula.

It is clear from the formula that a move

FIGURE 2. A 21-layer quarterwave stack has a

maximum uniformity error of 2% with a spherical

surface. The wavefront predicted purely by geometry

is convex and ellipsoidal with a maximum error of

just over one tenth of a wave. When the phase shift

from the coating is taken into account, the true

wavefront shows slightly less curvature than the purely

geometrical prediction.

1307LFW_28 28 7/3/13 1:26 PM

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to the new 843-R power meter for

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to beam position and offers a broadband,

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Refectance (%)

400 500 600 700

Wavelength (nm)

90

96

98

92

94

100

Software&Computing

29Laser Focus World www.laserfocusworld.com July 2013

to still higher angles of incidence would

improve the performance in an illuminat-

ing cone. A move to 63° would improve

performance by a factor of four. But this

implies a more difficult system design in-

volving rather more glass, and as a result,

the 45° incidence angle is much preferred

by system designers.

Uniformity problems

The uniformity of deposition thickness

in a coating machine follows laws sim-

ilar to those of illumination; techniques

of masking, along with moving substrates

and even sometimes sources, are used

to reach the necessary uniformity tar-

gets. Even with the best attention to detail

and the most advanced equip-

ment, there can be residual vari-

ations in thickness across a coat-

ed part; these can sometimes

have unexpected consequences.

Like the polarization effects de-

scribed earlier, these effects are

completely calculable by a suit-

able computer model.

We can illustrate some of the

sometimes-unexpected effects

on optical performance by ex-

amining two different front-

surface thin-film-interference

reflecting coatings. We shall as-

sume that these coatings are de-

posited over a completely flat substrate

of 30 mm diameter and that there is a ra-

dial error in the thickness of the coating

such that the resulting surface is spheri-

cal with a drop from center to periphery

of about 2%. We assume that the parts

are illuminated at normal incidence by

a perfectly collimated monochromatic

wave. Geometrical considerations tell us

that the resulting wavefront should now

be ellipsoidal with a variation of exactly

double that in the coating.

The first coating is a simple quarter-

wave stack. This is the basic reflecting

interference coating. Here, the overall

physical thickness of the 21-layer coat-

ing of alternate tantala and silica quar-

terwaves, with 510 nm as reference wave-

length, is 1.53 µm. At 550 nm, a reflected

wavefront based on geometrical consid-

erations only would have a maximum

error of 0.11 waves. But we also need

to include the phase on reflection; when

that is taken into account, the maximum

FIGURE 3. Spectral reflectance across the visible

region is shown for a 41-layer extended zone reflector.

The reflector consists of two quarterwave stacks

centered on 460 and 600 nm, separated by an

intermediate-thickness low-index layer.

1307LFW_29 29 7/3/13 1:26 PM

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‐0.2

‐0.1

0.1

0.0

0.2

0.3

0.4

0.5

0.6

Geometrical

Wavefront error (waves)

‐10 ‐5 0 5 10 15

Position (mm)

552 nm

556 nm

561 nm

547 nm

Software&Computing

July 2013 www.laserfocusworld.com Laser Focus World 30

wavefront error is actually slightly less

(see Fig. 2). The quarterwave stack is a

kindly coating with few surprises.

We can increase the spectral range of

high reflectance by combining two or

more quarterwave stacks into one coat-

ing to create an extended-zone high re-

flector (see Fig. 3). However, over part

of the range, the light will penetrate into

the coating to be reflected at some depth.

This results in quite rapid changes in

phase with wavelength, which is trans-

lated into rapid changes with total thick-

ness. Figure 4 shows some of the con-

sequences. Here we have, once again, a

2% maximum error in uniformity with a

regular spherical surface. This coating is

3.15 µm thick and the geometrical calcu-

lation shows a convex wavefront

with, at 550 nm, a maximum er-

ror of just over 0.2 wave. However, vary-

ing the wavelength slightly gives actual

wavelength shapes that are very differ-

ent—and in many cases concave rather

than convex—and quite different from

spherical or ellipsoidal.

Although the fundamental model of

thin-film interference has been with us

for a long time, innovations and elab-

orations are still being made. Software

products that do the calculations for us

and in so doing free us from the massive

burden of calculation are far from stat-

ic. The calculations in this article were

all carried out by the Essential Macleod

software package for thin-film design,

manufacture, and analysis.

REFERENCE

1. A. Macleod, “Thin film polarizers and polari-

zing beam splitters,” Society of Vacuum Coat-

ers Bulletin, Issue Summer, 24–27 (2009).

Angus Macleod is president and CEO of

Thin Film Center, Tucson, AZ; email: angus@

thinfilmcenter.com; www.thinfilmcenter.com.

FIGURE 4. A purely geometrical

calculation at 550 nm of the

wavefront reflected from the

extended zone coating, with its

uniformity error of 2%, shows

that it should be convex and

ellipsoidal with a maximum error

of around 0.2 waves. However,

taking the phase properties of the

coating into account and varying

the wavelength slightly from 550

nm, we find a rapidly changing

wavefront shape that is certainly

far from spherical or ellipsoidal.

1307LFW_30 30 7/3/13 1:26 PM

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1307LFW_31 31 7/3/13 1:26 PM

1307LFW_32 32 7/3/13 1:26 PM

High-end forecast of worldwideshipments of smart glass products

(Unit shipments in thousands)

Source: IHS IMS Research April 2013

49.6

2012 2013 2014 2015 2016

124434

2170

6619

33Laser Focus World www.laserfocusworld.com July 2013

P H O T O N I C S A P P L I E D : D I S P L A Y S

Head-worn displays: Useful tool or niche novelty?

GAIL OVERTON

Head-worn displays such as Google

Glass from Google’s (Mountain View,

CA) Project Glass are just now reach-

ing the consumer: the first Google

Explorer Editions ($1500) are roll-

ing off the assembly line to a select

audience of trial users. And while

initial responses have been positive,

the future seems uncertain for these

“augmented reality” devices—per-

haps much like the ‘tenuous’ pene-

tration of 3D technology in cinema

and smart devices.1

In April 2013, market research firm

IHS iSuppli (El Segundo, CA) forecast

that nearly 10 million smart glasses

would ship between 2012 and 2016

(see Fig. 1).2 Initial revenues, they say,

will be driven by sales to developers,

with sales increasing 250% in 2014 as

Google Glass products be-

come publicly available.

But Google isn’t the only

company betting on a sol-

id future for these photon-

ic-intensive electronic gad-

gets: the Vuzix (Rochester,

NY) M100 Smart Glasses

are under $500; Epson’s

(Long Beach, CA) Moverio

BT-100 display is designed

for in-home video view-

ing; and Innovega’s

(Bellevue, WA) iOp-

tic augmented reali-

ty contact lenses are

several years away

(2015), but attempt

to reduce the size of

the head-worn de-

vice by projecting information di-

rectly into the wearer’s eye. There

is even a hands-free Golden-i head-

set developed by Kopin Corporation

(Westboro, MA) with multilingual

speech recognition, gesture inter-

face, on-demand night vision, infra-

red thermal vision, facial recognition,

GPS, and passive health monitor-

ing. A Golden-i Police Pro applica-

tion from Ikanos Consulting (West

Bridgford, England) could give this

technology real longevity.3

Nomenclature

Before launching into commercial

(and emerging) head-worn display

options and non-proprietary technol-

ogy features, a note about terminolo-

gy would be helpful. Specifically, head-

worn display (HWD) products are

also named head-mounted displays

(HMDs), head-up or heads-up dis-

plays (HUDs), augmented reality (AR)

devices or displays, smart glasses, dig-

ital glasses, eyeglass displays, or even

wearable computers. Is there a differ-

ence in these named technologies?

“It is generally agreed that heads-

up displays or HUDs are those devic-

es intended for military/aircraft use

to augment the pilot’s other available

navigation devices,” says Jannick

Rolland, professor of Optics and

Biomedical Engineering and direc-

tor of both the R.E. Hopkins Center

for Optical Design & Engineering

and the planned NSF Center for

Freeform Optics, all in The Institute of

Optics at the University of Rochester

(Rochester, NY). Rolland has been

developing head-worn display device

technology for nearly 23 years—some

in partnership with industry players

NVIS (Reston, VA) and Revision

Military (Essex Junction, VT)—and

continues to advance HWD technol-

ogy. In recent years, she partnered

While initial responses to commercial

head-worn displays such as Google

Glass have been positive, only time will

tell if these products gain immediate

traction or follow a slow march into

consumer favor much like 3D technology.

FIGURE 1.

Driven by Google’s

lead, nearly 10

million smart

glasses or head-

worn displays are

forecast to ship

between 2012 and

2016. (Courtesy of

IHS iSuppli)

1307LFW_33 33 7/3/13 1:27 PM

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July 2013 www.laserfocusworld.com Laser Focus World 34

DISPLAYS cont inued

with Optical Research Associates (now

Synopsys, Mountain View, CA) to cre-

ate a path for real-time warping of ste-

reo distortion-free images as well as a

wireless version of the company’s HWD

prototype.4-6

“Head-worn displays or HWDs refer

to those devices meant for more con-

sumer-related and sports applications

like surfing the Internet, checking the

time or vital statistics, and getting alerts

for appointments using a device worn

on the head that acts like a computer to

‘augment’ the user’s surroundings,” adds

Rolland. “That is, an ‘augmented reality’

device is a more futuristic name for any

HWD products that are meant to easi-

ly and seamlessly integrate information

into the user’s field of view. Currently,

Google is on a path to commercialize AR

HWDs, and many other industry giants

are on that similar path.”7

Note that many consumer devic-

es are still named “heads-up displays”

even though they are not used in a mil-

itary/defense application; indeed, the

nomenclature confusion will subside

as the early adoption phase passes for

this personal display technology. Due

to the proprietary nature of military

HUD devices, the discussion that fol-

lows is concerned primarily with con-

sumer HWD applications.

A day in the life

You’re getting ready to step outside and

take the bus to work and wouldn’t want

to forget your smartphone—and smart

glasses. You slip them on and immedi-

ately get a visual text alert in your field

of view and an audio message remind-

ing you of your 9 am teleconference. You

have a little time while sitting on the bus,

so you call up your HWD Facebook app

and find out what’s happening by using

eye or voice cues to scroll through the

postings viewed in your glasses as you

note the long lines at the Starbucks on

the next corner. You play that hilarious

cat video again and call up your Twitter

app to let the world know just how fun-

ny it is by Tweeting the YouTube video

link by typing it into your smartphone.

Somehow, you’ve managed to strike up a

FIGURE 2. Google Glass is now available

for limited release to beta testers. (Courtesy

of Google)

1307LFW_34 34 7/3/13 1:27 PM

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35Laser Focus World www.laserfocusworld.com July 2013

DISPLAYS cont inued

conversation with the person sitting next

to you and so use your HWD to take

a picture of them and apply facial rec-

ognition software (and hopefully, their

verbal permission) to friend them on

Facebook.8 For lunch today, you’ll do the

healthy thing and head to the gym where

your smart glasses will display your cur-

rent weight, respiration rate, and other

vitals you’ve programmed into the health

monitor that interfaces with your glasses.

While the scenario here is hypotheti-

cal and representative of what some con-

sumer-targeted smart glasses intend to

do, Recon Instruments (Vancouver,

BC, Canada) launched the first con-

sumer HUDs for sports enthusiasts in

late 2010. Precision GPS and altimeters

guide ski enthusiasts, for example, with

1 m precision as their MOD Live HUD

displays speed, vertical descent, and

jump airtime while avoiding soggy pa-

per trail maps. Inserted into any Recon

Ready goggle, MOD Live gives wear-

ers an 84º unobstructed view; prism op-

tics project microdisplay data to appear

as if viewed on a 14 in. screen from a

distance of 5 ft. Announced at the May

2013 Google I/O developer’s conference,

the next-generation Recon Jet is target-

ed at a broader consumer audience and

anticipated to be faster and smaller with

live activity tracking, video streaming,

web and smartphone connectivity, and

Facebook integration.

Perhaps the most hyped of all HWD

devices is Google Glass—a monocular

display worn over one ear that transmits

images and videos to a small screen (0.75

in. deep, 0.375 in. wide and tall, or half

an inch at the diagonal) situated between

your eyebrow and upper lid (see Fig. 2).

The wearer glances up and to the right to

view the display with a resolution equiv-

alent to a 25 in. high-definition screen

seen from 8 ft away and touch and voice

controlled via a bone conduction trans-

ducer, according to Internet resources

(Google would not provide further tech-

nical details citing the beta pre-release

status of the product).9

In its United States Patent Application

20130044042, however, Google does

describe a binocular (assumed future

version) HWD “with an external im-

age viewable through the prism” that

could incorporate gyroscopes or other

sensors and, in alternative embodiments,

“the lens elements… may include: a trans-

parent or semi-transparent matrix dis-

play, such as an electroluminescent dis-

play or a liquid crystal display, one or

more waveguides for delivering an im-

age to the user’s eyes, or other optical

elements capable of delivering an in fo-

cus near-to-eye image to the user … or

additionally, a laser or LED source and

scanning system could be used to draw

a raster display directly onto the retina

of one or more of the user’s eyes.”

“Google Glass is targeted at social ac-

tivities—take a picture, take a 10-second

video, read a tweet, see an SMS text, an-

swer your phone; but Golden-i was de-

veloped as a powerful ‘hands-free’ tool

with the sophistication of a Ferrari [or]

a Porsche, and as robust as an Abrams

tank when required,” says Jeff Jacobsen,

VP of technology at Kopin Corporation.

Water- and dust-resistant Golden-i gen-

eration 3.8 headsets from Kopin are op-

erated using voice commands and head

FIGURE 3. Golden-i headsets offer a full PC

experience with enhanced synthetic vision,

speech recognition, and ambient noise

cancellation, allowing hands-free immediate

access to notebooks or your desktop and

server. (Courtesy of Kopin Corporation)

1307LFW_35 35 7/3/13 1:27 PM

www.fermionics.comFermionicss

4555 Runway St. • Simi Valley, CA 93063 Tel (805) 582-0155 • Fax (805) 582-1623

Opto-Technology

July 2013 www.laserfocusworld.com Laser Focus World 36

DISPLAYS cont inued

movements captured and understood

by a nine-axis MEMS tracker, all inter-

connected to other remote devices and

the Internet by WiFi, Bluetooth, and

Verizon 4G LTE wireless interfaces (see

Fig. 3). The monocular display can be

worn below or above the left or right

eye and is compatible with reading glass-

es, safety glasses, hard hats, or helmets.

With a quarter high-definition (qHD)

full-color transmissive thin-film transis-

tor (TFT) LCD microdisplay (960 × 540

resolution) that looks like a 15 in. laptop

screen situated about 18 in. away from

the user’s eye, Golden-i targets more

industrial applications as a computing

and communications tool. Incidentally,

Vuzix M100 Smart Glasses and Recon

goggles and Jet glasses all incorporate

Kopin displays, backlights, and in some

cases optics, and offer similar function-

ality to Google Glass.

Also with hands-free operation, or-

ganic light-emitting diode (OLED)-

based bidirectional microdisplay HMD

data eyeglasses from the Fraunhofer

Research Institution for Organics,

Materials and Electronic Devices

(COMEDD; Dresden, Germany) won

CeBIT’s Innovation Award IT among

4900 submissions and will enable a

gardener to immediately identify the

winged insect that just ate through its

petunias by surfing the Internet via

“gaze control” or eye tracking.

Because OLED microdisplays inte-

grate highly efficient light sources with

photodetectors on a CMOS backplane,

the COMEDD HMD device can pres-

ent and capture images at the same time

(see Fig. 4). Its smart glasses incorpo-

rate a 640 × 480 VGA-resolution color

OLED microdisplay (8 µm square pixels)

with a 10.2 mm × 7.7 mm physical dis-

play area in a 39.1º (horizontal) × 26.6º

(vertical) see-through (50% transparen-

cy) field of view. The nested photodiode

pixels enable an embedded camera with

128 × 96 pixel resolution.

The Fraunhofer COMEDD HMD de-

velopment team also included Trivisio

Prototyping (Trier, Germany) for the

binocular, see-through optics de-

sign and the Fraunhofer Institute of

Optronics, System Technologies and

Image Exploitation (IOSB; Karlsruhe,

Germany) for its eye-tracking technol-

ogy. In addition to the OLED microdis-

play with embedded photodiodes, the

FIGURE 4. Bidirectional OLED-based data eyeglasses allow the user to interact with the

Internet or other smart data using “gaze control” or eye tracking for truly hands-free operation

(a). Photodetectors as well as OLED display pixels are integrated onto a CMOS 50% transparent

backplane (b) to both display and capture images. (Courtesy of Fraunhofer COMEDD)

a) b)

Photodiode

OLED pixel

1307LFW_36 36 7/3/13 1:27 PM

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37Laser Focus World www.laserfocusworld.com July 2013

FIGURE 5. The Z800 3DVisor—while it

proved too bulky for widespread consumer

use—was the forerunner of HWD OLED-

based devices that are now being improved

for consumer use with higher contrast and

brightness, wider field of view, and lower

power consumption than alternative LCD or

LCOS technologies. (Courtesy of eMagin)

glasses also house a 5.6 × 11.2 mm eye-

motion box that captures an image of

the user’s right pupil and projects it to

a photodetector matrix. The embedded

camera converts the image to a digital

data stream and a mobile computer uses

an eye-tracking algorithm to calculate

coordinates and extract the user’s point

of gaze to control the display.

OLED HWD proponents also include

eMagin (Bellevue, WA) with its Z800

3DVisor aimed at the PC gaming market

(see Fig. 5). “While the product proved

to be too bulky for widespread consumer

use, the 40 degree diagonal field of view

and greater-than-HD WUXGA [1900 ×

1200] resolution make eMagin OLEDs

the microdisplays of choice for the U.S.

Army and military organizations around

the world for night-vision goggles, situ-

ational awareness HMDs, and thermal

weapon sights,” says R. Bruce Ridley,

eMagin VP of business development

and special projects. “Backlight-free,

low-power-consumption, active-matrix

OLED microdisplays enable head-worn

displays with high pixel count, wide field

of view, and high contrast.”

Privacy and distraction?

We’ve already seen how texting while

driving can be deadly. So how about

driving while wearing your HWD or

even walking down the street? In a re-

cent Insight Media (Norwalk, CT)

Display Central article, Phil Wright says

that the former primary concern of de-

velopers as to whether the “geeky eye-

wear” would be widely adopted by con-

sumers is now being replaced—as the

technology matures and the geek factor

becomes less of an issue—by “implica-

tions to privacy and safety matters.”10

Wright describes how “recent press

accounts cite some specific privacy con-

cerns that may or not become hot topics

with the emergence of wearable always-

on image capture and display devices.

For example, several observers have in-

quired whether it would be appropriate

to wear Glass in a public restroom.” And

as for safety issues, Wright considers that

“for recreational eyewear users like ski-

ers and snowboarders, the concern that

injuries may result from distracted high-

velocity users is legitimate.”

Only time will tell how well HWD

technology is adopted, and, like cell

phones, laws will no doubt be written

to control when, where, and how the

devices are used. In this early stage of

development, Wright says it best when

he concludes, “The social norms that

should accompany the adoption of such

wearable always-on technology are not

yet established, understood and widely

applied.”

REFERENCES

1. See http://bit.ly/11mQOHm; http://bit.ly/

yEIHdv; and http://dailym.ai/OMuMTZ.

2. See http://bit.ly/12pAXqF.

3. See http://huff.to/ZXkSXn.

4. J. Rolland and O. Cakmacki, Optics &

Photonics News, 20, 4, 20–27 (April 2009).

5. A. S. Bauer, Opt. Exp., 20, 14, 14906–14920

(2012).

6. J. P. Rolland et al., “See-Through Head Worn

Display (HWD) Architectures,” Handbook

of Visual Display Technology, 2145–2170,

Springer, New York, NY (2012).

7. See http://bit.ly/11Cl9zi.

8. See http://bit.ly/11zU3Xr.

9. See http://cnet.co/11ONKBm.

10. See http://bit.ly/16Erkd8.

1307LFW_37 37 7/3/13 1:27 PM

The Next Generationof Optical Filters

1-855-4ALLUXA

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PerformancePriced Right.

1307LFW_38 38 7/3/13 1:27 PM

Probe frequency (cm-1)

Pumpfrequency

(cm-1)

21002060202019801940

2100

2060

2020

1980

1940

AB

C

FTIR

39Laser Focus World www.laserfocusworld.com July 2013

ULTRAFAST TUNABLE LASERS

2D infrared spectroscopy moves toward mainstream useMARTIN ZANNI, CHRIS MIDDLETON, MARCO ARRIGONI, and JOSEPH HENRICH

Two-dimensional infrared (2D IR)

spectroscopy has many advantag-

es over commonly used forms of IR

spectroscopy. As an analytical tool,

it can help identify compounds and

disentangle mixtures. As a research

tool, it can provide both kinetic and

structural information, such as what

is needed for research in biophysics,

drug binding and membrane dynam-

ics, and materials science—for exam-

ple, organic LEDs (OLEDs) and or-

ganic photovoltaics.

Until very recently, the technique

was characterized by daunting prac-

tical complexity, limiting its use to a

small handful of specialized ultra-

fast laser-spectroscopy labs. The re-

cent development of a

user-friendly 2D IR in-

strument now makes

2D IR spectroscopy al-

most as routine as estab-

lished techniques such

as Fourier-transform IR

(FTIR) or nuclear-magnetic-resonance

(NMR) spectroscopies, unlocking its

vast potential for a broad range of users.

What is 2D IR spectroscopy?

The predecessor to 2D IR spectros-

copy is FTIR spectroscopy, which is

currently one of the most widely used

analytical and research tools in the

world. FTIR spectroscopy is often the

first tool that a researcher uses to ana-

lyze a new compound, check whether

a chemical reaction has completed, or

determine whether or not a molecule

has bound to a surface.

Nearly every molecule

that vibrates produces a

characteristic IR absorp-

tion spectrum, and so FTIR has uses

in fields as diverse as biophysics, mate-

rials science, energy sciences, and ana-

lytical chemistry. Catalogs have been

compiled containing the FTIR spectra

of thousands of molecules so that un-

known compounds can be identified.

However, one of the things that can-

not be learned from FTIR is whether

two absorption lines come from the

same molecule or not.

Consider the FTIR spectrum in

Fig. 1 (top), which contains three

peaks labeled A, B, and C. Are these

three peaks all created by the same

molecule? Or do they arise from the

mixture of different types of mole-

cules? Reference spectra can help, as

can additional experiments, and of-

ten enough is known about the sam-

ple to eliminate some possibilities, but

A unique method to investigate

molecular structure and dynamics

has become a practical research tool,

thanks to the advent of user-friendly,

integrated 2D IR spectrometers.

FIGURE 1. Experimentally measured (top) FTIR and (bottom) 2D

IR spectra are shown for a mixture of compounds. From the FTIR

spectrum, one cannot determine how many types of molecules are

contained in the mixture. In contrast, the 2D IR spectrum exhibits a

pair of diagonal peaks for each of the peaks in the FTIR spectrum.

The cross-peaks in the 2D IR spectrum reveal that the two higher-

frequency peaks are coupled to one another, meaning that the

vibrational motions of these two modes influence one another; this

usually occurs when two modes reside on the same molecule. In

fact, these spectra were collected for a mixture of two compounds.

Absorbance A is due to W(CO)6 and peaks B and C are from a

rhodium dicarbonyl (RDC). One does not see cross-peaks between

W(CO)6 and RDC because the mixture is too dilute. (Data collected

by Tianqi Zhang)

1307LFW_39 39 7/3/13 1:27 PM

Probefrequency

Pumpfrequency

t3t2t1

Pump Probe

July 2013 www.laserfocusworld.com Laser Focus World 40

ultrafast tuNaBlE lasErs cont inued

without further information, an FTIR

spectrum cannot unequivocally answer

this fundamental question.

Two-dimensional IR spectroscopy is

able to answer this question, and many

others, by providing a dynamic and 2D

picture of how the absorption peaks are

connected with each other.1 A typical 2D

IR spectrum (see Fig. 1, bottom) is a 2D

map in which molecular absorption is

plotted as a function of two excitation

frequencies covering the same wavelength

(or wavenumber) range. The peaks ob-

served along the diagonal line are similar

to a conventional FTIR spectrum, while

the off-diagonal structures (called cross-

peaks) are created by the interactions or

energy flow between vibrational energy

levels. The dynamic evolution of the sys-

tem, such as energy flow or chemical ex-

change, can be monitored by varying the

time delay between the combination of

pulses used to excite the sample.

Going back to the example of Fig. 1,

each of the three peaks in the FTIR spec-

trum creates a diagonal pair of peaks in

the 2D IR spectrum. The pairs of cross-

peaks between B and C (connected by

a square) indicates that these two ab-

sorbances arise from one species, while

peak A, which is not connected by any

cross-peaks, belongs to a second spe-

cies. In fact, these experimental spectra

were measured for a dilute mixture of

tungsten hexacarbonyl [W(CO)6] and

rhodium dicarbonyl (RDC) in acetone.

W(CO)6 has a single absorption band at

1670 cm-1, whereas RDC has two ab-

sorption bands at 1990 and 2070 cm-1.

Thus, the cross-peaks help disentangle

the FTIR spectrum.

Where do these cross-peaks come

from? The cross-peaks measure the cou-

pling between vibrational modes.1 In

the example above, modes B and C of

RDC come from the stretches of the two

carbonyl groups attached to the metal

center. Because of their close proxim-

ity and because they share a common

central atom (the metal), the vibration-

al motions of one carbonyl mode influ-

ences the motions of the other.2 That is

what is meant by coupling. As a result,

a cross-peak appears between the two.

Cross-peaks can also occur between

molecules if the vibrational modes of

those molecules become intertwined,

such as often occurs between hydro-

gen-bonded species, stacked aromatic

ring systems (such as in DNA), and oth-

er sorts of structural arrangements such

as protein secondary structures. Thus,

like an FTIR spectrum, a 2D IR spec-

trum provides frequency and intensity

information, but in addition also reveals

the connectivity between bonds.

How does one collect

a 2D IR spectrum?

The principles behind 2D IR spectrosco-

py are relatively straightforward. If two

vibrational modes are coupled, excita-

tion of one of those modes with a la-

ser pulse should change the frequency

of the other one. If that happens, there

is a cross-peak. In fact, this is how the

first 2D IR spectra were generated: the

frequency of a tunable narrowband mid-

IR laser pulse was scanned across the vi-

brational resonances while monitoring

the absorption of a probe pulse.3 The

change in absorption or optical densi-

ty (ΔOD) was plotted as a function of

the narrowband frequency to give probe

and pump axes, respectively (see Fig. 2).

This frequency-domain approach of

collecting 2D IR spectroscopy is still be-

ing used, although it is now largely being

replaced by a time-domain version that

is much more accurate. In the time-do-

main approach, the narrowband pulses

in Fig. 2 are replaced with pairs of femto-

second pulses whose bandwidth covers

all the vibrational modes at once.

Data are collected as a function of

the time delays t1 and t3. The time-do-

main data are then processed by taking

a Fourier transform to present the spec-

trum in a similar manner to how an FTIR

instrument processes its interferograms.

Instead of replacing the probe with a pair

of pulses, it is also possible to use a single

femtosecond pulse and a monochroma-

tor so as to optically produce the Fourier

transform of the probe axis.

The time-domain approach is usually

preferable to the frequency-domain ap-

proach because the narrowband puls-

es are picoseconds in duration, during

which most molecules move and lose a

substantial amount of their energy (see

Fig. 3). Thus, the signal is stronger and

the spectra more easily interpreted.

Implementing 2D IR

spectroscopy using

pulse shaping

In principle, what we have described

above is straightforward to do exper-

imentally, but in practice it has taken

more than 10 years to learn the best and

simplest ways of implementation. To im-

plement the time-domain pulse sequence,

one needs to generate four beams of

FIGURE 2. The conceptually simplest way

to collect a 2D IR spectrum is to scan the

frequency of a pump pulse and monitor the

change in absorbance of a probe pulse.

FIGURE 3. Modern 2D IR spectra are

usually collected in the time domain by

replacing the pump and probe pulses in

Fig. 2 with a pair of femtosecond pulses

whose bandwidth spans all the vibrational

modes of interest. The time delays (t1 and

t3) between the pulses are scanned and

the data Fourier-transformed. In principle,

identical spectra should be obtained

with either the frequency of time-domain

methods, but in practice femtosecond

pulses produce much higher-quality spectra.

1307LFW_40 40 7/3/13 1:27 PM

1307LFW_41 41 7/3/13 1:27 PM

ωprobe (cm-1)

ωpump

(cm-1)

1700165016001550

1700

1660

1620

1580

A

A

B

B

C

C

D

D

FTIR

July 2013 www.laserfocusworld.com Laser Focus World 42

ultrafast tuNaBlE lasErs cont inued

femtosecond pulses, control their rela-

tive delays with accuracies of a few fem-

toseconds, focus them all into the sample

at the same spot, and then direct the sig-

nal onto a detector. This process is even

more difficult when considering that the

laser beams are in the mid-IR, and thus

invisible to the naked eye.

Building a spectrometer from scratch

can take months for even the best exper-

imentalist, and when assembled, if a sin-

gle mirror is bumped, it can take days to

get the signal back. A laser system that

generates the mid-IR light is also critical,

because high beam stability is mandato-

ry to keep temporal and spatial overlap

of these four pulses. Thus, the great po-

tential of 2D IR spectroscopy has been

hampered by experimental complexity.

A technique that combined the best

of both worlds—femtosecond pulses

with a simple optical layout—was in-

vented a few years ago when the Zanni

Research Group at the University of

Wisconsin-Madison used femtosecond

pulse shaping to collect a 2D IR spec-

trum.4 Femtosecond pulse shaping was

invented nearly two decades ago; Martin

Zanni built the first pulse shaper that op-

erates in the mid-IR by using an acous-

to-optic modulator made of germanium.

Using this pulse shaper, his research

group generated and scanned the time

delay between the pairs of femtosecond

pulses in Fig. 3 to generate a 2D IR data

set. Moreover, they showed that spec-

tra could be collected in a pump-probe

beam geometry in which the two pump

pulses (and probe pulses) are collinear,

rather than having separate beam paths

for each of the four pulses. Thus, their

experimental design enabled comput-

er-generated pulse sequences (similar to

how an NMR spectrometer generates ra-

dio-frequency pulses) and reduced the

number of laser beams from four to two.

It has become apparent over the past

five years that this method offers many

other advantages as well. The pulse

shaper can update the time delay with

every laser shot, eliminating the need

for mechanical translation stages and

resulting in faster data collection and a

higher signal-to-noise ratio. The phas-

es of the pulses can be cy-

cled, allowing the back-

ground to be subtracted

without chopping the laser

beams; this effectively in-

creases the repetition rate

and allows scatter from

heterogeneous samples to

be removed. In addition,

more sophisticated pulse

sequences can be generat-

ed that enable mixed fre-

quency/time-domain data

collection and the coherent

control of molecular vibra-

tions, for example.

Reducing complexity

Not surprisingly, the com-

plexity with which 2D IR

spectrometers were orig-

inally built limited their

use to a few specialty ul-

trafast-laser labs. Two key

developments have com-

bined to enable the devel-

opment of user-friendly 2D IR spectrom-

eters. First, the availability of intense and

stable mid-IR laser sources such as the

Libra, provided by Coherent: the Libra is

a one-box integrated regenerative ultra-

fast amplifier that produces highly sta-

ble pulses at the millijoule energy level

with less than 100 fs duration at kilo-

hertz repetition rates.

The laser’s output is directed into a

pre-aligned optical parametric amplifier

(OPA) such as the Coherent OPerA Solo

(TOPAS), which generates femtosecond

mid-IR pulses. These pulses span 150

cm-1 or more and are tunable over the

2.6–11 µm range. Thus, with computer-

controlled software, the mid-IR pulses

can be set to cover the vibrational modes

of interest.

The other key development consist-

ed of developing a similarly user-friend-

ly 2D spectrometer. The 2DQuick, by

PhaseTech Spectroscopy, is the first

closed-box 2D IR spectrometer; it used

pulse shaping technology from the Zanni

Research Group discussed above.5 This

instrument has two acousto-optic mod-

ulators, one to generate the pump pulses

and the other the probe pulses.

By using two pulse shapers, either axis

of the 2D IR spectrum can be collected

in the frequency or time domains, and

thus the best method of scanning can

be selected based on the properties of

the molecules. Moreover, phase cycling

can be performed for either the pump or

probe pulses, thereby optimizing back-

ground subtraction.

For most academic research groups it

takes one or two years to build a 2D

IR spectrometer, skilled laser experts

to maintain it, and a deep knowledge

of the nonlinear formalism to program

the data-collection software. In contrast,

2DQuick collects a 2D IR spectrum in

seconds and produces publication-qual-

ity data in just a few minutes for many

molecular systems (averaging may be

required, depending on signal strength

for the molecule of interest). The soft-

ware comes with a collection of standard

pulse sequences used by the 2D IR com-

munity, or users can program their own

FIGURE 4. Infrared spectra of the amylin polypeptide

associated with type 2 diabetes are shown in two forms:

(top) a FTIR spectrum; (bottom) a 2D IR spectrum with

regions highlighted by boxes that correspond to peptide

secondary structures. Peak C is created by an isotope label

at Ala-13. Its cross-peaks linked to A and B but not D reveal

that it is located in a β-sheet of the fiber.

1307LFW_42 42 7/3/13 1:27 PM

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43Laser Focus World www.laserfocusworld.com July 2013

pulse sequences. The spectral range of

the standard instrument covers the 3–8

µm wavelength range, with other rang-

es available upon request.

This spectrometer enables a broad

range of scientists to utilize 2D IR spec-

troscopy. For non-experts, it is a us-

er-friendly blackbox. For spectroscopy

experts, it enables them to easily imple-

ment their own custom-designed pulse

sequences to explore new ideas. For in-

stance, one could optimize a pulse se-

quence using concepts from coher-

ent control to maximize vibrational

excitation.

Example applications

Although in its relative infancy, 2D IR

spectroscopy has already proven to be

a powerful tool in delivering insights on

some important scientific problems. In

life sciences, for example, it is known

that diseases such as Parkinson’s, Type

II diabetes, “mad cow” disease, and

Alzheimer’s, are associated with anom-

alous folding and/or aggregation behav-

ior of amyloid proteins, specifically the

way that these proteins stick together

to form secondary structures such as

β-sheets.

In another example, 2D IR spectra

were used to characterize the fiber-for-

mation kinetics of the human islet amy-

loid polypeptide (hIAPP) that is involved

in type II diabetes.6 Spectroscopic mark-

ers were identified that uniquely moni-

tor random coil versus β-sheet secondary

structures, as well as probe β-sheet elon-

gation and stacking (see Fig. 4). These

measurements provided more rigorous

kinetics for the secondary structure

evolution of amyloid formation than is

available with other techniques.

The 2D IR approach has also recent-

ly been used to study the influenza vi-

rus.7, 8 Specifically, it was used to exam-

ine the pH-controlled M2 protein from

influenza A that is a critical component

of the virus, and serves as a target for the

aminoadamantane anti-flu agents that

block its proton channel activity. 2D IR

data revealed that trans-membrane pro-

teins undergo a very subtle, but specif-

ic, conformational shift when this chan-

nel is closed.

Many 2D IR researchers have been

focusing on the structural dynamics of

liquids and proteins, but materials-sci-

ence applications are a promising new di-

rection. In materials sciences, molecular

conformations at organic/inorganic in-

terfaces play a vital role in certain emerg-

ing technologies, ranging from solar cells

to molecular electronics such as OLED

displays. However, studying conforma-

tions of molecules adsorbed to materi-

als is very difficult. 2D IR spectroscopy

was used to identify three conformations

of an organic dye on a titanium diox-

ide (TiO2) polycrystalline thin film, and

monitored the electron injection kinetics

for each.9 Electron transfer in polymer

photovoltaics has also been studied.10

ACKNOWLEDGEMENT

All of the data shown in this article was

collected using spectrometers at the

University of Wisconsin-Madison that

became the basis for the product called

2DQuick Array.

REFERENCES

1. P. Hamm and M. Zanni, Concepts and

methods in 2D IR spectroscopy, Cambridge

University Press, Cambridge, England (2011).

2. O. Golonzka et al., Phys. Rev. Lett., 86, 10,

2154 (2001).

3. P. Hamm et al., J. Phys. Chem. B, 102, 31,

6123 (1998).

4. S.-H. Shim et al., Proc. Nat. Acad. Sci., 104,

14197 (2007).

5. D. R. Skoff et al.,“Simplified and economical

2D IR spectrometer design using a dual

acousto-optic modulator,” Chemical Physics,

in press.

6. D. B. Strasfeld et al., J. Am. Chem. Soc., 130,

6698 (2008).

7. A. Ghosh et al., Proc. Nat. Acad. Sci., 108,

6115 (2011); doi:10.1073/pnas.1103027108.

8. J. Manor et al., Structure, 17, 247 (2009).

9. W. Xiong et al., J. Am. Chem. Soc., 131,

18040 (2009).

10. L. W. Barbour et al., J. Phys. Chem. B, 110,

24281 (2006).

Martin Zanni and Chris Middleton are at

PhaseTech Spectroscopy (www.phasetech-

spectroscopy.com) and the Department of

Chemistry, University of Wisconsin-Madison;

Marco Arrigoni and Joseph Henrich are at

Coherent, Santa Clara, CA; e-mail: marco.

[email protected]; www.coherent.com.

1307LFW_43 43 7/3/13 1:27 PM

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Position in fber (m)

1.41.21.00.80.60.40.20

100500

80400

60300

40200

20100

00

Pump power (mW)

Forward ASE (mW)

Backward ASE (mW)Upper-statepopulation (%)

45Laser Focus World www.laserfocusworld.com July 2013

FIBER-OPTICS TEST & MEASUREMENT

Specifications guide active and passive optical fiber characterization

RÜDIGER PASCHOTTA

For many applications of optical fi-

bers, it is vital to know various de-

tails. Consider an ytterbium (Yb)-

doped fiber, into which only a pump

wave is injected (see Fig. 1). Even in

this simple situation, the fiber behav-

ior is already rather complicated: as a

function of varying pump power, am-

plified spontaneous emission (ASE)

and upper-state excitation of the Yb

ions vary greatly. Measurements re-

veal that backward ASE extracts sub-

stantial power, but the effect of for-

ward ASE would not be seen as the

emission is largely reabsorbed in the

fiber before it reaches the end. In ef-

fect, pump absorp-

tion exhibits surpris-

ing variations caused

by saturation effects

of ASE light.

Only with a nu-

merical model based

on reliable fiber data

can such details be

well understood. The

model will then reveal

performance-limit-

ing factors and fa-

cilitate the planning

of prototype tests so

that desired results are ob-

tained without too many

costly and time-consum-

ing test iterations. To that

end, certain essential opti-

cal and spectroscopic fiber

properties need to be mea-

sured. Some straightforward

specifications such as outer

fiber diameter and coating details are

not discussed here, as these are easy

to understand and usually have no in-

fluence on optical fiber performance.

Propagation losses

If light is to be sent through long

lengths of fiber, the propagation loss-

es (in dB/km) are relevant. A simple

measurement of output power and

incident power is not sufficient be-

cause coupling light into the fiber

may also cause substantial unknown

losses. This problem is often solved

with cutback measurements. One first

launches light into a longer length of

fiber and measures the transmitted

power. Then one cuts the fiber back

to a substantially shorter length and

measures the power again. The dif-

ference can be attributed to the prop-

agation losses in the length by which

the fiber was shortened. Using a white

light source and a spectrometer, one

obtains the propagation losses for a

range of wavelengths.

Another option is to launch light

with a known efficiency, measured in

previous tests. Obviously, rather longer

fibers make it easier to obtain precise

loss data. Time domain reflectome-

try is another solution, but requires

more sophisticated equipment.

For active fibers, the optical power

of the probe light must be low enough

to avoid significant excitation of the

laser-active ions and the resulting sat-

uration effects. Also, the high losses in

absorption bands of laser-active ions

enforce the use of short fiber lengths;

light in cladding modes may then get

The use of optical fibers—in fiber

lasers, for example—is greatly

facilitated by their proper

characterization. The resulting data

are the foundation for optimized

device designs and efficient product

development.

FIGURE 1. The

evolution of pump

power, forward- and

backward-amplified

stimulated emission

(ASE) power, and the

upper-state population

in an ytterbium (Yb)-

doped fiber that is

pumped at 920 nm are

shown. The simulation

was done with RP

Fiber Power software.

1307LFW_45 45 7/3/13 1:42 PM

Singlemode fber

Core

Cladding

1-855-4ALLUXA www.alluxa.com

PerformancePriced Right.

Optical Filters

July 2013 www.laserfocusworld.com Laser Focus World 46

FIBER-OPTICS TEST & MEASUREMENT cont inued

to the end of the fiber. Particularly if the

core absorption is strong and the fiber

is stripped, light in cladding modes can

spoil the results. One then needs to take

special precautions to attenuate light in

cladding modes, for example, placing a

drop of index-matching fluid on the fi-

ber to let light escape on the side.

Singlemode cutoff

A singlemode fiber supports only one

guided propagation mode per polar-

ization direction. Below a certain cut-

off wavelength, additional higher-order

modes are supported. The simplest meth-

od for measuring the cutoff wavelength

is to measure the intensity spectrum

of transmitted light when a white light

source is used as the input. Below the

cutoff, the transmitted powers are higher

because more modes capture more light.

With a tunable laser source, the cut-

off can be seen more precisely. In the

singlemode regime, the spatial profile

of the transmitted light is very smooth.

Below the cutoff wavelength, it be-

comes asymmetric and strongly wave-

length-dependent due to interference

effects between the modes.

Mode size, core size,

and fiber NA

For singlemode optical fiber applications,

the size of the guided mode is normal-

ly more relevant than the core size; the

latter is not clearly defined for smooth

profiles. The guided mode is too small

for a direct accurate measurement, but

one can simply measure the beam diver-

gence of light exiting the fiber (see Fig. 2).

One can usually assume an approximate

Gaussian beam for which the divergence

half-angle is defined as λ/(πw0), where

λ is the wavelength

in the medium and

w0 is the beam ra-

dius at the beam

waist. For exam-

ple, for a mode

radius of 5 µm at

1550 nm, the diver-

gence half-angle is

approximately 0.1

rad or 5.7°. At a distance of 5 cm, the

mode will already have expanded to a

radius of 5 mm.

The numerical aperture (NA) is not

very relevant for a singlemode fiber. It

is even useless if the user does not know

how it is defined for a fiber with a

smooth index profile.

Multimode fibers

Multimode fibers are more difficult

to characterize, partly because the in-

put light always excites some mixture of

modes, with the power distribution de-

pending on the launch conditions.

For step-index fibers with large cores,

the core size and the NA are normally

well known from production. The NA is

most easily obtained from the refractive

indices of core and cladding as measured

on the preform. From the core radius

and NA, one can calculate the relevant

mode properties such as the number of

modes and range of group indices.

Graded-index fibers are more chal-

lenging. A refractive index profile, pos-

sibly measured on the preform and res-

caled to the fiber dimensions, can be

helpful, as it allows the numerical calcu-

lation of mode properties. Propagation

losses will generally depend on the mode.

Measuring mode-dependent losses is dif-

ficult, however.

Chromatic dispersion

For some applications, particularly with

singlemode fibers, the chromatic disper-

sion is of high interest. A relatively direct

measurement method is the pulse delay

technique, where one measures time de-

lays for ultrashort pulses with different

center wavelengths to obtain the differ-

ences in group delay. A similar method

FIGURE 2. It is hard to determine the exact spot size of a laser

beam required to efficiently launch into a singlemode fiber, but it

is easy to find out the divergence of the light exiting the fiber by

measuring the beam radius at some distance after the fiber.

1307LFW_46 46 7/3/13 1:42 PM

47Laser Focus World www.laserfocusworld.com July 2013

is the phase shift technique, where one

measures the time delay of an intensi-

ty modulation. Usually, however, such

measurements are limited to narrow

wavelength regions.

Most convenient for chromatic dis-

persion measurements in wide wave-

length regions is white-light interferom-

etry. The fiber under test (a singlemode

fiber) is incorporated in one arm of a

Michelson interferometer with a white

light source. The output power is record-

ed with a simple photodetector while the

arm length difference is scanned. An ad-

ditional interferometer precisely moni-

tors the length changes. With a Fourier

transform, one can extract the chromat-

ic dispersion in the full wavelength range

of the light source. The spectral reso-

lution is limited by measurement noise,

and is thus higher if a high-intensity

light source such as a superluminescent

diode is used. A modified method (spec-

tral interferometry) uses a spectrometer

instead of a simple detector, making the

scanning of an arm length unnecessary.

Transition cross-sections

The pump absorption in a rare-earth-

doped fiber depends on the doping pro-

file, the mode size, and the wavelength-

dependent absorption cross-sections. For

a fiber laser or amplifier, the total ab-

sorption in dB/m is not the only relevant

parameter, as saturation effects cannot

be calculated from absorption alone.

One also requires absorption cross-sec-

tions and the core overlap factor, or at

least the product of both; that product

determines how strongly the optical field

interacts with the laser-active ions. As an

example, absorption and emission cross-

sections are shown for Yb3+ ions in ger-

manosilicate glass (see Fig. 3).1

Often, the ab-

sorption is mea-

sured easily, and

the overlap can be

estimated, but the

dopant concentra-

tion is not known.

Its measurement

in the small core

of a fiber is hard;

it is more realis-

tic to do that on a

preform. Another

possibility is to fab-

ricate a homoge-

neously doped sam-

Wavelength (nm)

Cross-sections (pm2)

110010501000950

Emission

900

2.5

3.0

2.0

1.5

1.0

0.5

0.0

Absorption

FIGURE 3. Absorption and emission cross sections are shown for

ytterbium (Yb3+) in germanosilicate glass.

With a Fourier transform, one can extract the

chromatic dispersion in the full wavelength

range of the light source. The spectral resolution

is limited by measurement noise, and is thus

higher if a high-intensity light source such as

a superluminescent diode is used. A modified

method (spectral interferometry) uses a

spectrometer instead of a simple detector, making

the scanning of an arm length unnecessary.

1307LFW_47 47 7/3/13 1:42 PM

Time (ms)

Fluorescence intensity (a.u.)

2015 30251050

0.8

1.0

0.6

0.4

0.2

0.0

July 2013 www.laserfocusworld.com Laser Focus World 48

FIBER-OPTICS TEST & MEASUREMENT cont inued

ple, make a chemical analysis of it to

learn the doping concentration, and ob-

tain the absorption cross-sections of the

laser-active ions from the measured ab-

sorption. One may then assume that the

cross-sections are essentially the same

for the fibers in order to calculate the ef-

fective doping concentration from a fi-

ber’s transmission spectrum.

For some more complicated laser-

active ions, multiple metastable levels

can be relevant, and the cross-sections

for excited-state absorption need to be

known. These are more difficult to mea-

sure than ground-state absorption cross-

sections, since the ions need to be excited

into some higher level and the fraction

of the ions in that level is not usually

known. Fortunately, there are modula-

tion techniques that can solve this mea-

surement problem.

Measurement of the fluorescence spec-

trum taken from the side of the fiber can

give the shape of the emission cross-sec-

tion’s curve (taking into account a factor

of λ-5 for the translation from emission

cross-section to fluorescence intensity in

microwatts per nanometer). The abso-

lute scaling may be obtained using the

reciprocity principle, for example.

Upper-state lifetime

Another relevant quantity is the lifetime

of the excitation of the upper-laser level

(and sometimes further metastable lev-

els). For long-lived states, it can be suffi-

cient to monitor the fluorescence of the

laser-active ions

with a detector on

the side of the fiber,

while a continuous-

wave pump laser

beam is modulat-

ed with a rapid-

ly rotating chopper

wheel. The use of a

pulsed pump laser

is better for short-

lived levels (see Fig.

4). Note that the

fluorescence decay

is not necessarily

exponential: ini-

tially, it may be faster if upconversion

processes via ion-ion interactions take

place. One will then obtain shorter life-

times when measuring with stronger ex-

citation and when using only the high-in-

tensity part of the decay curves.

It is generally advisable to compare

the measured lifetime with the radia-

tive lifetime as computed from the emis-

sion cross-sections. A shorter measured

lifetime may result from parasitic de-

cay processes, whereas a longer mea-

sured lifetime indicates inconsistency

of the results.

Double-clad fibers

Additional complications arise for dou-

ble-clad fibers, where the pump light

is injected into an inner cladding and

has an accordingly reduced overlap

with the doped fiber core. The result-

ing pump absorption is reduced due

to the limited overlap and is strongly

mode-dependent.

Therefore, it is actually not well char-

acterized by a simple wavelength-de-

pendent absorption coefficient, except

if strong mode mixing is obtained as a

result of a suitable fiber design such as

one with a D-shaped or octagonal inner

cladding. With strong bending of the fi-

ber, mode mixing and thus pump ab-

sorption may be enhanced.

Better characterization needed

Unfortunately, many commercial opti-

cal fibers do not come with proper spec-

ifications for essential details, partic-

ularly concerning spectroscopic data.

The required know-how is not trivial

and is not always available in-house. It

is common to specify only the fiber’s

absorption at one or two wavelengths

such as a common pump and signal

wavelength, whereas cross-section data

are often not presented. Some manufac-

turers can at least offer data for their

most popular fibers.

For commonly used Yb-doped fi-

bers, the chemical core compositions

vary little from the data shown previ-

ously in Fig. 3. Some absorption fig-

ures then serve to determine the doping

concentration. This may already be suf-

ficient for quite accurate modeling re-

sults. The situation is more difficult for

erbium (Er)-doped fibers because they

have more variable chemical composi-

tions. Note also that fiber data can vary

substantially between different fabrica-

tion runs if the fabrication conditions

are not stable. The device performance

may then also be inconsistent.

It is often remarkable how limited

the available data are for optical fiber.

For example, one can hardly imag-

ine a manufacturer of electronic chips

who leaves it to his/her customers to

find out exactly how these chips be-

have in common active or passive ap-

plications. Specialty fiber technology

is a field where relatively small quan-

tities are sold, and manufacturers of-

ten hesitate to invest heavily in fiber

characterization. It would be more ef-

ficient, though, if the manufacturers

rather than the users would measure

these data in order to facilitate the de-

velopment of fiber devices.

REFERENCE

1. R. Paschotta et al., IEEE J. Quantum Electron.,

33, 7, 1049 (1997).

Rüdiger Paschotta is founder and execu-

tive of RP Photonics Consulting, Waldstras-

se 17, 78073 Bad Dürrheim, Germany;

e-mail: [email protected]; www.

rp-photonics.com.

Tell us what you think about this article. Send an

e-mail to [email protected].

FIGURE 4. Temporal variation of the intensity of the fluorescence of

erbium ions is shown for excitation with a nanosecond pump pulse.

1307LFW_48 48 7/3/13 1:42 PM

OWNED & PRODUCED BY: PRESENTED BY:

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YYYTTTYYLL TLILIL TIBILBILGR LEXFLEXIBL BBEXIBEXIBG ATREAREAGR RATEATERAA R FR FLRR EEFLLGRGGG IXXIG

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DADATATA R RATATESES EER DADAATREAATEER GGGRGREA TEESS AAATAA RRAATEESDA SSRGR

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51Laser Focus World www.laserfocusworld.com July 2013

PHOTONIC FRONTIERS: SILICON PHOTONICS

Silicon photonics evolve to meet real-world requirementsJEFF HECHT, contributing editor

Silicon photonics is evolving as it

emerges from the laboratory to be-

come a real-world technology. The

basic thrust remains the same, to in-

tegrate photonic and electronic com-

ponents on a silicon-based platform

to transmit high volumes of data at

low cost. However, developers are re-

fining the technology to circumvent

the inherent performance limitations

of silicon and to meet evolving appli-

cation requirements.

It’s a time of weighing techno-

logical alternatives, trying to devel-

op standards for the near term, and

considering how to meet future needs.

With electrically pumped silicon

emitters still not in the cards, one key

choice is between piping light from

external sources and

bonding III-V emitters

onto silicon. Others in-

clude designing devices,

fabrication techniques,

and transmission pro-

tocols that balance sil-

icon capabilities, with

user requirements that

match selections of transmission pro-

tocols, which balance silicon capabil-

ities and user system requirements.

Driving forces

The driving force behind silicon pho-

tonics remains the inexorable growth

of computing power and digital data

transmission. The main needs today

are for backplane connections in high-

performance computers and for trans-

mission within data centers.

Computing performance hit one

important performance wall a few

years ago. Processing cores cannot

perform more than a few billion op-

erations per second without requir-

ing active cooling. That forced de-

signers to shift to multicore chips

and increasingly parallel operation,

even for personal computers. High-

performance computers require

massive parallelism with extensive

The goal remains the same:

integrating photonics with electronics

to cut costs and improve data-link

performance. But developers have

accepted the need for compound

semiconductor light sources, bonded

to silicon or external to the chip.

FIGURE 1. Magnified view of

IBM silicon nanophotonic chip

fabricated with 90 nm technology.

The red feature at the left side of

the cube is a germanium detector

fabricated on silicon. The blue

feature at right with the beam

entering it is the modulator. Yellow

areas are conductors. The small

red dots at lower right are silicon

transistors. (Courtesy of IBM)

1307LFW_51 51 7/3/13 1:43 PM

1000

100

10

12015200519951985

Number of components per chip

Year

Indium phosphideDoubles every

2.6 years Hybrid siliconDoubles every

1 year

July 2013 www.laserfocusworld.com Laser Focus World 52

PHOTONIC FRONTIERS: SILICON PHOTONICS cont inued

movement of data among backplanes

within the system. Data centers and

server farms used for cloud computing

similarly have massive needs for high-

speed data transmission among many

machines.1

New data-center standards are being

developed with serial rates of 25 Gbits/s

per channel, says Yurii Vlasov, manag-

er of the Silicon Nanophotonics Project

at the IBM Watson Research Center

(Yorktown Heights, NY). Silicon tech-

nology is not going to reach higher line

rates for at least five years, he explains.

“So it’s not important to increase the

capacity per channel. What you need

is to show scalability in the number of

channels and in the degree of WDM

[wavelength-division multiplexing],

so you need less fiber per channel. We

need denser and more integratable

technology.”

The sheer number of connections in

a data center makes cost crucial. What

counts is the “total cost of the solution,”

Vlasov says. That includes modules, sig-

nal conversion from electronic into op-

tical format and back again, and cable.

Packing more channels into each fiber

using WDM and other techniques be-

comes more important at distances lon-

ger than several tens of meters, where

cable become a large part of total cost.

Scaling to 100 Gbit/s Ethernet

IBM sees 25 Gbit/s silicon photon-

ic modules as a fundamental build-

ing block for a new generation of fi-

ber systems transmitting 100 Gbit/s

and up on many parallel channels over

singlemode fiber. Early versions of

100 Gigabit Ethernet transmitted 10

Gbit/s over each of 10 multimode fi-

bers at 850 nm for short-haul transmis-

sion. The new 802.3bm proposal sets

25 Gbit/s transmission on each of four

wavelengths spaced 20 nm apart in the

1310 nm band through up to 500 m of

singlemode fiber.

At the IEEE International Electron

Devices Meeting in December 2012,

IBM described fabrication of the first

such module using complementary met-

al-oxide semiconductor (CMOS) tech-

nology with 90 nm geometry.2 The

module included four coarse WDM

channels spaced 850 GHz apart in the

1500–1550 nm range and filters with

flat tops 500 GHz wide. Detection was

with a germanium photodiode, compat-

ible with CMOS processing, having 3

dB input bandwidth of more than 20

GHz, and followed by a transimped-

ance amplifier, limiting amplifiers, and

an output buffer.

“All the functions are on the chip ex-

cept the laser, which is the optical pow-

er supply,” says Vlasov. Input signals

are coupled into the module through

the germanium photodiode, and an

external continuous-wave laser is an

“optical power supply” coupled to the

transmitter through

the modulator (see

Fig. 1). The module

also includes WDM

filters, waveguides,

crossings, direction-

al couplers, and ver-

tical grating couplers.

In addition to ben-

efitting from billions

of dollars invested

in silicon technolo-

gy, Vlasov says the

IBM approach also

benefits from two

other factors. Use

of a single die al-

lows standard pick-

and-place assembly

techniques, greatly

reducing packaging

costs. The design also accommodates

standard microelectronic techniques

that can test components during assem-

bly, before costly packaging is finished.

Looking forward to 400 Gigabit

Ethernet, Vlasov envisions transmit-

ting 25 Gbit/s signals on 16 chan-

nels spaced more closely, but still al-

lowing operation at temperatures of

0° to 70°C without significant cross-

talk. He says scaling from 100 to 400

Gbit/s “is a question of design rather

than technology.”

Hybrid silicon photonics

An alternative approach is molecular

bonding of III-V gain material direct-

ly to the silicon, adding light sources

and gain to the CMOS silicon platform,

plus offering new options for modula-

tion and detection. Adding the III-V

material requires steps outside the stan-

dard silicon processing, but also inte-

grates the two more tightly. Most work

has focused on indium phosphide mate-

rials for 1.3 or 1.55 µm bands.

“Hybrid silicon now has the same per-

formance as pure indium phosphide,”

says Martijn Heck of the University of

California at Santa Barbara (UCSB;

Santa Barbara, CA). The number of

components integrated on InP sub-

strates has been doubling every 2.6

years, but hybrid silicon integration has

been doubling every year since the first

demonstration less than a decade ago,

two decades after the first InP integra-

tion (see Fig. 2).3

So far, the best developed hybrid sil-

icon photonics are fabricated on sili-

con on insulator (SOI) substrates (see

Fig. 3). Bonding the III-V junction

just above a silicon waveguide cre-

ates a hybrid waveguide that couples

light generated in the III-V active re-

gion into a different mode that resides

FIGURE 2. Photonic integration on hybrid silicon got a late

start, but it is catching up to indium phosphide. The plot shows

the number of components per chip, which are doubling every

year for hybrid silicon but only doubling every 2.6 years for InP.

(Courtesy of Martijn Heck7)

1307LFW_52 52 7/3/13 1:43 PM

Hybrid waveguideTapered mode converter

SOI waveguide

SOI circuit

III/V diode withquantum wells

Metal contacts onsilicon dioxide

53Laser Focus World www.laserfocusworld.com July 2013

PHOTONIC FRONTIERS: SILICON PHOTONICS cont inued

entirely within the silicon. In a post-

deadline paper at the Conference on

Optical Fiber Communications in

March 2013, Aurrion (Goleta, CA) re-

ported hybrid silicon integration, in-

corporating both an array of eight un-

cooled 1.3 µm band lasers fixed at 200

GHz intervals for data communica-

tions, and a tunable laser in the 1.55 µm

band for telecommunications.4 In the

same session, Skorpios Technologies

(Albuquerque, NM) described its own

tunable hybrid silicon laser in the 1.55

µm band. Intel (Santa Clara, CA) has

demonstrated what it calls “a fully

functional” hybrid silicon photonics

module operating at 100 Gbit/s.5

John Bowers’ group at UCSB also is

developing a new generation of hybrid

silicon photonics based on silica-on-

silicon technology, which allows fab-

rication of silicon nitride waveguides

with as low as 0.05 dB/m and other

higher-performance components in-

cluding array waveguides (AWGs) and

ring-filter arrays. At the OFC 2013

postdeadline session, UCSB described

a 400 Gbit/s WDM receiver made

with that approach. They fabricated

a low-loss silicon nitride strip wave-

guide sandwiched between silica layers

to make an array waveguide capable

of demultiplexing

eight channels

separated by 400

GHz, then added

InGaAs photode-

tectors capable

of detecting 50

Gbit/s. That al-

lowed the module

to process a 400

Gbit/s signal.6

“This opens a

new perspective

for applications,”

says Heck. “We

are working on

microwave pho-

tonics, narrow-

band radio-fre-

quency generators

with low phase

noise.” The ultra-low-loss waveguide

technology also benefits development of

narrow-line or ultrastable modelocked

lasers. In principle, it could allow de-

velopment of integrated ring resonators

with Q factors of a few hundred mil-

lion. The AWG could be combined with

III-V optical amplifiers to make oscilla-

tors with multiple output wavelengths.

Silicon photonics were conceived for

data center communications, but with

performance now on a par with indium

phosphide, Heck says, “more high-per-

formance telecommunications applica-

tions are within reach.”

UCSB also is developing free-space

beam-steering silicon photonics for

DARPA’s Sweeper project. Large-scaled

phased arrays of grating emitters with

their beams emitting from the chip sur-

face would be steered by electro-optical

phase modulators a few orders of mag-

nitude faster than conventional MEMS

devices. Although power would be lim-

ited, the technology could be useful in

inter-chip data links.

Defining silicon photonics

for the future

Many challenges remain for silicon pho-

tonics. The tradeoffs between silicon

and III-V components are still being ex-

plored. Although CMOS-based silicon

fabrication technology is far more ma-

ture and economical, III-V materials

offer better speed and performance in

components including modulators and

detectors. How well can the silicon com-

ponents meet the high performance re-

quirements of telecommunications?

Current silicon photonics is limited by

temperature sensitivity of components

such as resonators or filters. Developers

are exploring how to reduce their tem-

perature sensitivity, and to reduce power

consumption of the silicon components

that generate much of the troublesome

heat. The heat generation that led to

multicore chips may limit the use of sili-

con photonics to link cores or chips.

Nonetheless, silicon photonics are be-

ing written into standards aimed at data

centers, where they can deliver much-

needed high-speed interconnections.

The technology is a serious contender

for future telecommunications systems

and for other low-power applications in

sensing and beam direction.

REFERENCES

1. Y. A. Vlasov, “Silicon CMOS-integrated

nano-photonics for computer and data

communications beyond 100G,” IEEE

Communications Magazine, 567–572 (Feb.

2012).

2. S. Assefa et al., “A 90nm CMOS integrated

nano-photonics technology for 25Gbps

WDM optical communications applications,”

IEEE International Electron Devices Meeting

(IEDM), postdeadline session 33.8, (December

10–12, 2012).

3 M. J. R. Heck et al., “Hybrid silicon

photonic integrated circuit technology,”

IEEE J. Sel. Topics Quant. Electron. V, 19,

6100117 (Jul./Aug. 2013); doi:10.1109/

JSTQE.2012.2235413.

4. B. R. Koch et al., “Integrated silicon photonic

laser sources for telecom and datacom,” OFC/

NFOEC 2013, postdeadline paper PDP5C.8.

5. E. Marchena et al., “Integrated tunable CMOS

laser for Si photonics,” OFC/NFOEC 2013,

postdeadline paper PDP5C.7.

6. M. L. Davenport et al., “A 400 Gb/s WDM

receiver using a low loss silicon nitride AWG

integrated with hybrid silicon photodetectors,”

OFC/NFOEC 2013, postdeadline paper

PDP5C.5.

7. M. J. R. Heck, M. L. Davenport, and J. E.

Bowers, “Progress in hybrid-silicon photonic

integrated circuit technology,” SPIE Newsroom,

doi:10.1117/2.1201302.004730 (2013).

FIGURE 3. Integration of a III-V optical amplifier with silicon on

a SOI chip. The top shows a cross-section illustrating how metal

contacts (yellow) apply a current across the III-V quantum wells

(red) to generate optical emission (whitish region). Bottom shows a

schematic of how tapered mode converters couple light between

the III-V hybrid waveguide and the silicon waveguide. (Courtesy of

Martijn Heck7)

1307LFW_53 53 7/3/13 1:43 PM

2013 CLEO/LASER FOCUS WORLD

INNOVATION AWARDS

Recognizing Photonics Innovators

FEATURED AT

CLEO:2O13Exhibition: 11–13 June 2013

San Jose, California, USA ®

SPONSORED BY:

CLEO:2O13

WINNER

KMLabs (Kapteyn-Murnane Laboratories)

Wyvern-HE compact femtosecond Ti:sapphire

regenerative amplifier system

For the development of the Wyvern-HE – a smaller, single-

stage, single-pump Ti:sapphire ultrafast amplifier delivering

performance (9mJ @ 1kHz, with adjustable repetition rate)

that has historically only been possible with much larger and

more expensive multi-stage designs.

HONORABLE MENTIONS

Femtolasers Produktions GmbH

First portable ultrafast Ti:Sapphire laser for biomedical applications

For the development of the INTEGRALTM CoreTM, the smallest commercially available sub-8 fs

ultrafast Ti:Sapphire laser delivering 200 mW average power with 300 MHz pulse repetition rate for

Terahertz, multiphoton microscopy, OCT, and spectroscopy applications.

Princeton Instruments

IsoPlane next-generation, aberration-free spectrograph

For the development of the IsoPlane SCT 320 Schmidt-Czerny-Turner spectrograph that

overcomes the limitations of traditional Czerny-Turner designs by totally eliminating field

astigmatism and greatly reducing coma and spherical aberration.

TAG Optics

TAG Lens 2.0: Using sound to shape light

For the development of an ultra-high-speed varifocal lens that can extend the depth-of-field of

conventional optical systems and enable user-selected focal lengths in micro-seconds through

acoustic refractive-index changes.

1307LFW_54 54 7/3/13 1:43 PM

SLM

Beamsplitter Object beam

Hologramplate

Hogel

Referencebeam

Combiner

Renderedimages

Diffuser

Mirror

Mirror Mirror

x-y

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Lasers

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55Laser Focus World www.laserfocusworld.com July 2013

BIOMEDICAL IMAGING

3D digital holograms visualize

biomedical applicationsJAVID KHAN

After 15 years of R&D, holograph-

ic technology is ready to re-emerge.

Digital holograms are now mature

enough for commercialization in all

sorts of fields including biomedical

imaging, scientific visualization, en-

gineering design, art, and advertis-

ing. In particular, three-dimensional

(3D) digital holograms can be created

from almost any type of biomedical

datasets from protein database files

to medical scans. Next-generation

holographic displays are being de-

signed for medical imaging to depict

volume data from computed tomog-

raphy (CT), magnetic resonance im-

aging (MRI), and ultrasound scans.

A holographic timeline

Scientific literature says that the best

way of making 3D images is to recre-

ate the light field of the scene.1 This

can be achieved through holography

and similar approaches

such as integral imaging.

Unfortunately, true

holography has not lived

up to its expectations,

which were largely driv-

en by the realms of sci-

ence-fiction fantasy fol-

lowing the iconic Star Wars movie in

1977. While static analog holograms

were popular for a while during the

1980s and 1990s, it soon became

clear that making static holograms

needed to move beyond the laborato-

ry and that dynamic holographic dis-

plays were “in a land far, far away.”

Hence, holography went under-

ground in the 1990s with just a few

European companies, some Japanese

groups, and the U.S. military devel-

oping digital hologram printing tech-

nology. Holographic display research

was performed only by high-end re-

search facilities like MIT Media Lab

(Cambridge, MA).

The recent proliferation of 3D con-

tent has created a resurgence of in-

terest in this field—a revival due to

the explosion of 3D data from many

sources including geographical data,

medical scans, CAD design, simula-

tions, low-cost depth scanners, cine-

ma/TV, and 3D printing.

Holoprinter technology

Digital holograms are fabricated us-

ing holoprinter or holographic print-

ing devices. These are industrial-scale

machines that can manufacture full-

color, purely digital-reflection ho-

lograms in a manner that is repeat-

able and reliable. Available from a

handful of manufacturers such as

Geola (Vilnius, Lithuania), View

Holographics (St Asaph, Wales)

and Zebra Imaging (Austin, TX),

Digital holograms—whether of DNA,

cells, full-sized organs, or even the

life-sized human body itself—can be

holographically printed for a range

of 3D analysis applications in the

biomedical industry.

FIGURE 1. The experimental

setup for a digital hologram

includes RGB lasers, a microdisplay,

beam-steering optics, and a

computer to show the images on

the microdisplay as well as control

the whole system.

1307LFW_55 55 7/3/13 1:43 PM

July 2013 www.laserfocusworld.com Laser Focus World 56

BIOMEDICAL IMAGING cont inued

holoprinters use a variety of techniques

to produce multiplexed stereographic

holograms from computer graphics or

real-world scenes.

The digital hologram comprises a ma-

trix of holographic pixels, also known

as holopixels or hogels. The holopix-

els are created by the interference of

red, green, and blue (RGB) lasers in a

holographic medium such as a photo-

polymer (by Bayer or DuPont) or sil-

ver halide film (see Fig. 1). A holoprint-

er includes RGB lasers, a spatial light

modulator (SLM), beam-steering op-

tics, and a computer to show the im-

ages on the SLM as well as control the

whole system. The laser-writing scheme

uses an object and reference beam pair.

The object beam is modulated via the

SLM with 2D information synthesized

from the scene. Optics are held station-

ary whereas the holographic medium

is mounted on an x-y translation stage

and moved relative to the lasers, which

are usually arranged vertically in-line

and operate on different holopixels in

parallel. The stage is moved continu-

ously in a raster-scan fashion.

Holopixels are written with RGB

pulsed lasers with pulse widths around

40 ns and energies up to 10 mJ. The

RGB holopixels are spatially overlaid,

with holopixel dimensions now shrink-

ing to submillimeter diameters—cur-

rently around 0.8 mm—and trending

even smaller to 0.5 mm or even 0.25

mm. At such small dimensions, the ho-

lopixels are no longer visible with the

human eye, making it possible to cre-

ate photo-realistic digital holograms.2 A

digital hologram fabricated in this man-

ner typically takes several hours for a

page-sized print.

For replay (viewing) of the 3D image,

digital holograms only require a simple,

bright point light source for illumination.

The holograms produced in this manner

are high-quality, full-color reflection ho-

lograms, and it is even possible to pro-

duce digital holograms that can lie flat,

allowing the viewer to walk 360° around

the image. A small page-sized digital

hologram costs a few hundred dollars

to produce, with larger images up to a

square meter scaling in price according-

ly. The price can be reduced further via

holographic replication technology that

works like a “holographic photocopier,”

with RGB lasers to make analog copies

of digital holograms in seconds.

Although current holoprinters are

somewhat bulky devices with large and

powerful lasers as well as mechanics,

portable devices are not far off. Pioneer

(Kawasaki, Japan) has announced a

desktop unit using RGB laser diodes

that can produce small card-sized ho-

lograms. There is every reason to ex-

pect desktop-sized holoprinters no larg-

er than a standard laser printer within

the next few years.

Digital holograms

Any type of 3D dataset can be convert-

ed to a digital hologram. This could be

a physical scan of an object, a math-

ematical description, molecular data,

map/contour data, point cloud, volume

data, CAD model data, or even a series

of stills or video.

First, the view of a 3D scene has

to be computed for each holopixel as

seen through its submillimeter aperture

by following a precise set of rules de-

pending on the holoprinter. For exam-

ple, a 200 × 300 mm page-sized holo-

gram with 0.8 mm holopixels requires

the generation of more than 90,000 2D

images. This is achieved using a combi-

nation of commercial computer model-

ing software with graphics rendering as

well as proprietary algorithms or cus-

tom hardware engines to perform a se-

ries of mathematical transformations to

generate the image data for presenta-

tion to the SLM.2

Since it is possible to control the light

rays emitted from each holopixel, it is

feasible to include some limited anima-

FIGURE 2. Using any 3D data file, accurate and to-scale 3D holographic models can span the gamut from green fluorescent protein to

human organs to a full anatomical model of the human body.

1307LFW_56 56 7/3/13 1:43 PM

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57Laser Focus World www.laserfocusworld.com July 2013

tion within the digital hologram such

as stripping away layers as the view-

er moves around the hologram, thus

revealing hidden aspects of the image.

As most of our images are synthetic, it

is also possible to include opacity and

fading to highlight features that would

otherwise be obscured.

From molecules to

anatomical models

Primarily targeted at public dissemina-

tion, outreach, training, and education,

Holoxica’s digital holograms span the

entire spectrum of biomedical science

from the atomic scale up to a full ana-

tomical figure (see Fig. 2).

A protein data base (PBD) file con-

taining all the necessary atomic (struc-

FIGURE 3. A digital hologram of the Rhind

mummy allows viewers to peel off the outer

wrapping and observe interior details of the

face and skull.

1307LFW_57 57 7/3/13 1:43 PM

a)

b)

July 2013 www.laserfocusworld.com Laser Focus World 58

BIOMEDICAL IMAGING cont inued

ture usually derived from x-ray crystal-

lography) and positional information

to describe the structure of atoms, mol-

ecules, and proteins can be used to re-

construct a geometrically accurate and

to-scale 3D model. Working in collab-

oration with Manchester University,

our first digital hologram in this area

was a green fluorescent protein (GFP).

We recently fabricated a digital holo-

gram of the well-known DNA double

helix structure to celebrate the 50th

anniversary of its discovery.

On a larger scale, Holoxica worked

with the Clinical Research Imaging

Centre (CRIC) at Edinburgh University

on a full-color digital hologram of a

pair of lungs from a CT scan. The in-

tricate detail of the structure is visual-

ized, including the bronchial tree and

lung sacks (pleura) surrounding the air-

ways (alveoli). We have also imaged the

liver (from ultrasound scans) and brain.

Our most complex hologram to date

is a full-length human anatomy holo-

gram created from a synthetic 3D mod-

el of a female. This hologram contains

three layers of information on the mus-

cle structures, skeleton complete with

arteries plus nervous system, and the

internal organs. One of the challenges

facing medical education is teaching the

3D structure of the body since most of

the material is currently in 2D.

Digital 3D holograms can also aid ar-

chaelogy. In 1857, the Rhind Mummy

was excavated from a tomb in Thebes

by the archaeologist Alexandar Rhind.

Despite remaining in its original wrap-

ping at the National Museum of

Scotland, the mummy’s secrets were

finally revealed 155 years later via CT

scans. The scans revealed that the Rhind

Mummy was an Egyptian female in her

late twenties, 1.58 m tall, and dating to

around 10 B.C. Holoxica managed to

produce an animated holo-

gram of the head and upper

torso that reveals different

layers of information as the

viewer moves from left to

right. The first layer is the

sarcophagus, or wrapping,

peeling away to reveal the

face followed by the skull

(see Fig. 3). This color-an-

imated, life-sized holo-

gram is currently on dis-

play at the MIT Museum

in Boston.

The future: dynamic,

real-time displays

Although the holographic

displays research commu-

nity has been making sig-

nificant advances in recent

years, the prospect of a true

holographic display still re-

mains elusive. Holographic

displays are still at the ba-

sic research stage and re-

quire significant techno-

logical advances before

they become commercially

feasible.1 Instead of trying

to make the “mythical Star Wars” dis-

play, we’ve taken a more pragmatic ap-

proach by asking, what is the simplest

holographic display you can make? The

answer: a single pixel, or voxel, in 3D

space, that can be switched on or off.

One voxel is not particularly interest-

ing, so we move on to two voxels and

work up from there to 4, 9, 16 voxels,

and so on.

Our first-generation proof-of-con-

cept holographic display demonstra-

tor in 2010 was based on a proprietary

holographic screen containing spatially

multiplexed interference patterns that

are easily switched by structured il-

lumination of the light source.3 The

second-generation display made earli-

er this year is based on a holographic

optical element (HOE), enabling free-

space imaging with arbitrary 3D imag-

es floating in mid-air that can change

in real time (see Fig. 4).4

Interactivity is added with a Kinect

motion sensor that allows people to

“touch” icons in space and draw objects

in mid-air. Immediate applications in-

clude head-up displays and novel user

interfaces with an added dimension.

The images are bright and visible un-

der indoor lighting conditions, and the

approach is scalable, leveraging exist-

ing manufacturing techniques and us-

ing high-end components with some

modifications.

REFERENCES

1. V. M. Bove, “Display Holography’s Digital

Second Act,” Proc. IEEE, 100, 4, 918–928

(2012).

2. H. I. Bjelkhagen and D. Brotherton-Ratcliffe,

Ultra-Realistic Imaging: Advanced Techniques

in Analogue and Digital Colour Holography,

Taylor & Francis Group, London, England

(2013).

3. J. Khan et al., “A low-resolution 3D

holographic volumetric display,” Proc. SPIE,

7723, 77231B-7 (2010).

4. J. Khan et al., “A real-space interactive

holographic display based on a large-aperture

HOE,” Proc. SPIE, 8644, 86440M (2013).

Javid Khan is founder and managing direc-

tor of Holoxica in the Scottish Microelectron-

ics Centre, The King’s Buildings, West Mains

Rd., Edinburgh EH9 3JF, Scotland; e-mail: jk@

holoxica.com; www.holoxica.com.

FIGURE 4. Holoxica’s second-generation holographic

display (a) enables free-space imaging with 3D images

floating in mid-air that can change in real time (b). A Kinect

motion sensor allows people to ‘touch’ and interact with

the objects.

1307LFW_58 58 7/3/13 1:43 PM

L A S E R S ■ O P T I C S ■ D E T E C T O R S ■ I M A G I N G ■ F I B E R O P T I C S ■ I N S T R U M E N T A T I O N

59Laser Focus World www.laserfocusworld.com July 2013

New productsWould you like to be included? Please send your

product description with high-resolution digital

image to: [email protected]

MEMS mirrorsOff-the-shelf, 4.2-mm-diameter MEMS mirrors are

now available in any quantity with either gold or alu-

minum coatings. The bonded, modular mirror can be

mounted on a variety of the company’s actuators, and

may be ordered in packages ranging from large 24-pin

dual-in-line (DIP24) to LCCs of different sizes.

Mirrorcle Technologies

Richmond, CA

www.mirrorcletech.com

Picosecond laserBrixX ps universal diode lasers feature completely

integrated driver electronics, precision temperature

regulation, and beam-shaping optics to emit pulses

down to 50 ps, pulses in the nanosecond range, and

up to 100 MHz digital and up to 1 MHz fast analog-

modulated continuous-wave emission. Diodes with

up to 1500 mW optical output power and wave-

lengths between 375 and 2300 nm can be used.

Omicron

Frankfurt, Germany

www.omicron-laser.de

M2 moduleThe Beamage-M2 uses

Fabry-Perot optics to

allow M2 factor measurement in less than a second

with no moving parts. Standard features include OD 4

attenuation, ISO 11136- and 13694-compliant calcu-

lations, a complete software package, and a Rayleigh

range of 50 μm–6 mm.

Gentec-EO

Quebec, Canada

[email protected]

Freeform micro-optics rapid fabrication serviceThe LightForge micro-optics fabrication service allows

optical designers to create a wide range of optical

elements and have the fabricated part shipped in as

little as two weeks. Freeform surfaces can be created,

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charges and prototyping

lead times.

PowerPhotonic

Dalgety Bay, Scotland

www.powerphotonic.

co.uk

1307LFW_59 59 7/3/13 1:46 PM

July 2013 www.laserfocusworld.com Laser Focus World 60

New products

Piezoelectric actuating stageThe Scan XY40 piezoelectric actuat-

ing stage offers a travel range of 40

μm per axis. Designed primarily for 2D

scanning applications, it has a resonant

frequency of >800 Hz per axis and is

suited for nanometer positioning of

lightweight optical components. The x-

and y-axes can be controlled separately.

Piezosystem Jena

Jena, Germany

[email protected]

UV lasersThe NANIO 355-6-V-80 offers 6 W of

laser power at 355 nm. It is designed

for micromachining applications like

glass cutting, ceramic drilling, sap-

phire scribing, or via hole drilling. The

NANIO 1342-8-V laser provides 8 W

of Q-switched 1342 nm laser power

for semiconductor and solar cell appli-

cations.

InnoLas Laser

Krailling, Germany

[email protected]

Galvanometers The QS-5 OPD, QS-7 OPD, and

QS-12 OPD scanning galvanometers

include patented optical position

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with either two- or three-axis heads.

Designed for a full range of optical

scanning requirements, these high-

speed, low-drift galvanometers are

used for industrial, medical, printing,

and life science applications.

Nutfield Technology

Hudson, NH

[email protected]

Fusion splicerThe FSM-100P+ fusion splicer for

optical fibers includes an end-view

fiber observation system. It is capa-

ble of splicing extra-large-diameter

fiber up to 1200 µm using Plasma

Zone Path Modulation. It also has

Split V-groove clamping systems,

enhanced sweep ARC technology,

and other features for glass process-

ing and fiber tapering.

Fujikura Europe

Chessington, England

www.fujikura.co.uk

1350 nm lasers1350 nm lasers are now available in

standard 19-emitter bars with total

power >40 W continuous-wave (CW)

and slope efficiency of >40%, single-

emitter 1350 nm sub-mounts with 6 W

CW power, and fiber-coupled products

that provide 4.8 W CW power. They

are designed for medical and commu-

nications applications.

SemiNex

Peabody, MA

www.seminex.com

emICCD cameraThe PI-MAX4 series of emICCD cam-

eras includes the 512EM version, which

provides single-photon sensitivity;

the 1024i for double-image featuring;

and the 1024 × 256 for spectroscopy.

Capabilities include <500 ps gating,

>30 frames/s, RF modulation, and

complete control via a LightField soft-

ware platform with an oscilloscope-like

user interface.

Princeton Instruments

Acton, MA

www.emiccd.com

Optical fiberDTG-LBL-1550-AGF is a low-bend-loss

fiber with densely spaced draw-tower

gratings (DTGs) over the full length

of the fiber. It is designed for use with

an optical frequency domain reflec-

tometry (OFDR) system that allows

measurements over a wide strain or

temperature range with spatial resolu-

tion down to a few millimeters over the

entire fiber length.

FBGS

Geel, Belgium

www.fbgs.com

EMCCD cameraThe Falcon Blue 1 Mpixel electron-mul-

tiplying CCD camera offers UV trans-

mission using a MgF2 window, which

will pick up signals as low as 180 nm.

1307LFW_60 60 7/3/13 1:46 PM

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61Laser Focus World www.laserfocusworld.com July 2013

New products

It is sensitive from the 180 to 1100 nm

range with QE of 24% at 200 nm. At

35 Hz full frame, it has readout noise

<1 e- with EM gain on.

Raptor Photonics

Larne, Northern Ireland

www.raptorphotonics.com

Laser rangefinderThe MLR 4K laser rangefinder is a SWaP-

optimized, military-grade ER:glass solid-

state laser device that can fire continu-

ously at up to 3 ranges/s. It measures

34 × 54 × 89 mm, weighs 118 grams

(without cover), and consumes less than

2 W when ranging, making it useful for

handheld systems, weapon platforms,

and stabilized turrets.

FLIR

Wilsonville, OR

www.fir.com

Spectroscopy softwareOceanView spectroscopy software

combines data processing capabilities

with a clear graphical user interface for

miniature spectrometers. Customizable

software includes a schematic view

that provides a visual roadmap of data

flow from spectral inputs to processed

results. It integrates temperature, volt-

age, and other input data, allowing

users to capture and visualize data

from multiple sources.

Ocean Optics

Dunedin, FL

[email protected]

Laser diode driverThe iC-HT two-channel CW laser

diode driver with a microcontroller

interface for medical and industrial

applications. Using this device, laser

diodes may be driven by the optical

output power, laser diode current, or

a full, controller-based power control

unit. Maximum laser diode current per

channel is 750 mA. With supply volt-

ages of 2.8–8V, it can drive both blue

and green laser diodes.

iC-Haus

Langenpreising, Germany

www.ichaus.com/ic-Ht

PhotodetectorThe BPDV3120R is a balanced photo-

detector offering a 3 dB bandwidth of

70 GHz. The optical front end consists

of a monolithic balanced photode-

1307LFW_61 61 7/3/13 1:46 PM

July 2013 www.laserfocusworld.com Laser Focus World 62

New products

tector chip with on-chip biasing. The

coaxial single-ended output can detect

up to 64 GBaud polarization diversity

x-QAM signals. The device supports

systems for next-generation networks

using 400 Gbit/s or 1 Tbit/s coherent

detection-based optical transmission.

u2t Photonics

Berlin, Germany

www.u2t.de

Optical muzzle flash detectorOptical detector technology is capa-

ble of perceiving muzzle flash from

over 100 m away, while minimiz-

ing false alarms. Operating at the

speed of light, the system provides

an almost instantaneous response to

a gunfire event, providing real-time

detection capabilities. The detectors

can be designed to reject any opti-

cal signals that are outside the desired

detection bandwidth.

Cal Sensors

Santa Rosa, CA

[email protected]

Handheld LIBS elemental analyzerThe LEA is a handheld elemental ana-

lyzer based on

laser-induced

breakdown

spectroscopy

(LIBS). It can

identify all ele-

ments, analyze

both conduct-

ing and noncon-

ducting samples,

and requires no sample preparation,

consumables, or cleaning between

tests. Applications include RoHS/

REACH compliance, forensics, explo-

sive materials identification, mineral

exploration, pharmaceutical manufac-

turing, and research.

Lasersec

Jarvas, Finland

www.lasersec-systems.com

Wavelength extension unitThe new SuperK EXTEND-UV wave-

length extension unit provides tun-

able light in the entire 270–400 nm

range with power levels on the order

of 10–100 μW. The collimated output

enables tight focusing and fast pulses,

down to 20 ps in length with vari-

able megahertz-range repetition rate,

making the unit suited for lifetime

measurements and studies of ultrafast

photochemical processes.

NKT Photonics

Birkerød, Denmark

www.nktphotonics.com

Broadband mirrorsThe Diflex 1100 and 2000 broadband

mirrors feature an absolute reflectance

>99% and an average reflectance

>99.5% for

all polariza-

tions over the

wavelength

ranges of

350–1100 nm

and 320–2000

nm, respectively. The angle of incidence

can vary between 0° and 45°. Coatings

are composed of metal-oxide coating

materials for high abrasion resistance

and chemical stability.

Optics Balzers

Balzers, Germany

www.opticsbalzers.com

SpectrophotometerThe PHOTON RT UV-VIS-NIR scanning

spectrophotometer is a universal instru-

ment designed specifically for unat-

tended measurement of optical parts

with coatings. The instrument can be

produced in six configurations relative

to the effective spectral range from

380–1700 nm up to 190–4500 nm.

EssentOptics

Minsk, Belarus

www.essentoptics.com

Flat-top stageThe H101F flat-top stage incorporates

a completely flat top plate, which

eliminates any obstacle to objective

rotation, while low-profile sample

holders allow the use of high NA

objectives. Embedded x- and y-axis

encoders provide closed-loop con-

trol, and miniature high-torque motors

allow for access to the condenser and

other microscope adjustments.

Prior Scientific

Rockland, MA

[email protected]

1307LFW_62 62 7/3/13 1:46 PM

63Laser Focus World www.laserfocusworld.com July 2013

industrial control service business. It is definitely the technical nature of my dad’s business, as well as his example of starting a self-sustaining independent business that gave me the confi-dence to start a business.

MC: What is your vision of applications outside of

discovery and development?

HK/MM: Our business has primarily been supplying advanced lasers for research, but we see this broadening to other uses. By focusing an intense femtosecond pulse into a gas to hit an atom very hard before it even has a chance to ionize, one can generate extremely high-order harmonics to wavelengths less than 8 Å. This is the only practical way to make essentially a table-top coherent x-ray laser, which is useful for everything from imaging for nanotechnology to metrology of thin films—as well as for basic science studies.

Just recently we received some good news—a notice of allowance for our patent on methods for extending the high-harmonic coherent x-ray generation technique to shorter wave-lengths into the x-ray region of the spectrum of interest for ultrahigh-resolution x-ray imaging and other nano applica-tions, which is another potential market.

Equivalently, femtosecond lasers are increasingly being used for precision industrial machining because they ablate away material before it has a chance to conduct heat away and cause collateral damage. The result is a clean and precise cut. Another application is precision spectroscopy using ultrashort pulses to generate frequency combs.

MC: Customer handholding must be a challenge.

HK/MM: Much of what we have accomplished has been through developing new technologies that are needed by cus-tomers to tackle hard scientific problems. Our customers are our source of fulfillment, but can also easily get us into trouble by tempting us with exciting challenges that push the limit! We are now able to make sure we can realistically evaluate the cost of taking on such interesting projects.

MC: Any issue working as a wife-husband team?

HK/MM: Being a husband-and-wife team in research is an ex-ceptional advantage—two smart people who trust each oth-er completely can vet ideas quite quickly. We very frequently don’t see eye to eye on issues, but the issues where we don’t tend much more to be real, substantive ones without a clear answer; i.e., the ones that deserve a good argument.

Regarding family and work issues, we don’t really segregate the two. We always feel fortunate that at least we see each other a lot, even when we are working way too hard. This is a generic problem with academe more so, I believe, than in the entrepreneurial world. The tenure clock and academic politics get in the way of family considerations, and ultimately there needs to be a better way.

MC: Ever thought about being part of an established

company?

HK/MM: There has been considerable consolidation in the laser market, and the time may come when being acquired is appro-priate. In the shorter term, our lasers and x-ray lasers are seeing increasing potential use, for example, for metrology in the semi-conductor industry. Finding a larger strategic partner to help de-velop our lasers for industrial application is something we have an active interest in. We feel that with the right partner, we could do much more, accelerate the development of novel, game-chang-ing technologies, and gain greater market penetration.

MC: I have found Boulder has been a good place for

Precision Photonics and MBio Diagnostics. What are the

pros and cons being in Boulder?

HK/MM: Boulder is an exceptional place to establish an ad-vanced R&D intensive company. There are great universities and institutes to collaborate with and hire students from such as the University of Colorado, NIST, the Colorado School of Mines, and Colorado State University. The cost of living is rea-sonable and the views, hiking, biking, and skiing are spectacu-lar. Moreover, there are many local optics companies, with a very supportive local government.

BUSINESS FORUM continued from page 68

1307LFW_63 63 7/3/13 1:51 PM

July 2013 www.laserfocusworld.com Laser Focus World 64

Manufacturers’ Product Showcase

New FCD561 Laser for Biotechnology

JDSU announces FCD561, the newest addition to the

popular frequency converted diode (FCD) family of

continuous-wave

lasers for life-

science applications.

FCD561 is available

in 30 mW free-space

and fiber-delivered

packages to meet

the most demanding

integration needs.

FCD561 uses

proven JDSU all-

in-fiber architecture, providing an extremely rugged device

in an energy-efficient, lightweight, and compact package.

Fiber-delivered versions incorporate unique end-of-fiber

optical power monitoring and polarization correction to

eliminate the effects of mechanically- and thermally-induced

birefringence.

For more information, e-mail James Christian, JDSU

senior product manager, at [email protected].

www.jdsu.com/go/fcd

Photon NanoScan™ 2 Scanning Slit Laser Beam Profiler

Ophir Photonics, global leader in precision laser

measurement equipment and a Newport Corporation brand,

introduces NanoScan 2, the new version of their scanning

slit beam

profiler. A NIST-

calibrated laser

beam profiler,

NanoScan

2 measures

continuous

wave (CW) and

pulsed beams

across the entire

spectral range,

from UV to far

infrared measuring beam sizes from microns to centimeters

at beam powers from microwatts to kilowatts, without

attenuation.

www.ophiropt.com/photonics • (866) 755-5499

One-year subscription to LASER FOCUS WORLD FREE!

Visit us online at www.lfw-subscribe.com

or call Customer Service at 847.559.7500

To TEC

Controller

To Pulse

DriverOutput module with

a socket-mounted

butterfly-packaged

diode installed.

Model AVO-9A-B40 mA/DIV1 ns/DIV

Nanosecond Laser Diode Drivers With Butterfly Diode Sockets

Each of the 19 models in the Avtech AVO-9 series of pulsed laser diode drivers includes a replaceable output module with an ultra-highspeed socket suitable for use with sub-nanosecond rise time pulses. Models with maximum currents of 0.1A to 10A are available with pulse widths from 400 ps to 1 us. GPIB, RS-232, and Ethernet control available.

Pricing, manuals, datasheets at

http://www.avtechpulse.laser

More information: [email protected]

1307LFW_64 64 7/3/13 1:51 PM

65Laser Focus World www.laserfocusworld.com July 2013

The FISBA Beam Twister™

The FISBA

Beam Twister™

(FBT) is an

innovative

beam shaping

element for

generating

an almost

symmetrical

beam profile

of laser diode bars. The FBT unit consists of a FAC lens

with a beam rotating lens array for nearly diffraction limited

collimation and best symmetrization. With the corresponding

focussing optics (also produced by FISBA) the laser power

can be coupled with an efficiency of more than 80% out

of a fiber with 400 micron diameter (NA 0.22) and more

than 70% out of a fiber with 200 micron diameter (NA 0.22).

Customized designs on pitch, fill factor, wavelength etc. are

available upon request.

www.fisba.com

919P Series Thermopile Sensors

Newport’s new 919P Series of Thermopile Detectors provide

a full range of sensors to meet the power measurement

needs for CW or pulsed lasers. They offer broadband,

spectrally flat response, with a maximum power range up

to 5000 Watts. These sensors are compatible with Newport

power meter models 1936-R/2936-R, 1928-C, 1918-R, and

the new 843-R. Each 919P thermopile sensor includes a

DB15 connector and internal EEPROM for storing factory

calibration data.

(800) 222-6440

www.newport.com

2 Micron High Power Q-Switched Fiber Laser

The world’s first 2 Micron High Power Q-Switched Fiber

Laser from AdValue Photonics is a turn-key system with

pulse energy up to 200 µJ, peak power up to 10 kW, and

pulse width as narrow as 20 nanoseconds with single

mode beam

quality. It is a

powerful tool

in a compact

package for

application

areas such

as nonlinear

optics, frequency conversion, spectroscopy, LIDAR, and

materials studies. AdValue Photonics is specialized in the

spectral region of 2 micron, offering fiber lasers, amplifiers,

broadband light sources, and passive components. Contact

us for more information at 1-520-790-5468 or sales@

advaluephotonics.com.

www.advaluephotonics.com

Powerlite Furie™ — the next generation High Energy Nd:YAG laser

Built on the proven Powerlite laser platform and using our

energy through efficiency approach, the Furie delivers 7J

of IR and 4J of green ensuring excellent beam profile and

overall performance that’s best-in-class in all aspects of

stability. This compact and robust laser is designed to

operate 24/7 for set-and-forget industrial applications while

providing flexibility and versatility required by scientific

users, making it ideal for Ti:Sapphire pumping and materials

processing applications.

Learn more at www.continuumlasers.com/furielp

1307LFW_65 65 7/3/13 1:51 PM

July 2013 www.laserfocusworld.com Laser Focus World 66

Business Resource Center

Holographic GratingsLaser tuning • Telecommunication

Pulse compression/stretching Monochromators • Spectroscopy

• High efficiency • Extremely low stray light

• Straight grooves with uniform profile, plane

and concave/convex

• Standard sizes 8 × 15 - 120 × 140 mm

• Custom made gratings according to spec’s

SPECTROGONSweden: [email protected]

Tel +46 86382800

USA: [email protected] Tel +1 9733311191

UK: [email protected] Tel +44 1592770000

www.spectrogon.com

Optics / Filters Manufacturing

Optical FiltersInfrared, VIS, UV

Bandpass • Longwave-pass Shortwave-pass • Broad-Bandpass

Neutral Density

•‑First quality production over-runs

•‑>100,000 filters for immediate delivery

•‑�Typical size 1 inch dia, most filters can be turned

down or diced to smaller dimensions

•‑�3 inch dia Si and Ge filter waters available for

specific wavelengths

•‑Custom design for prototype or OEM

Applications:

•‑Gas Analysis‑•‑Moisture Sensors

•‑�Emission/Environmental Monitoring

•‑Analytical Instruments‑•‑Process Control

•‑Medical/Clinical/Respiratory/Agricultural

•‑Alcohol Analyzers‑•‑Astronomical

•‑Laser Instruments‑•‑Machine Vision

•‑Thermal Imaging‑•‑Fluorescence

Optical CoatingsAnti-reflection • Beamsplitter

High reflections mirror

•‑Coating Service capabilities 193-20000 nm

SPECTROGONSweden: [email protected]

Tel +46 86382800

USA: [email protected] Tel +1 9733311191

UK: [email protected] Tel +44 1592770000

www.spectrogon.com

Holographic Gratings Optics / Coatings Manufacturing

1324 E. Valencia Dr. Fullerton, CA 92831

www.latticeoptics.com

T: 714-449-0532, F: 714-449-0531

[email protected]

Need optics & coatings?

Quality, quick service & any quantity24 hrs turnaround on most optics & coatings

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Excimer, YAG, CO2 optics. OPO, crystal & laser rod

coatings, prisms mirrors, windows, beamsplitters,

polarizing optics, waveplates, filters spherical,

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Catalog

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Lattice Electro Optics, Inc.

Put your products where your customers

are looking to buy. Sign up today for:

Contact Katrina Frazer at 603-891-9231 or [email protected]

FOCUS ON PRODUCTS

1307LFW_66 66 7/3/13 1:51 PM

ADVERTISING SALES OFFICES

Advertiser&web index

67Laser Focus World www.laserfocusworld.com July 2013

AdValue Photonics ..................................... 65

Alluxa ...................................................38, 46

Argyle International, Inc. ............................57

Avtech Electrosystems, Ltd. ...................... 64

Bristol Instruments, Inc. .............................18

Cambridge Technology, Inc. ........................ 8

Castech, Inc. ...............................................41

Coherent, Inc. ............................................ C4

Continuum ................................................. 65

Discovery Semiconductors, Inc. ................. 6

DRS Technologies .......................................19

Edmund Optics ...........................................10

Electro-Optics Technology, Inc. .................14

Fermionics Corporation ............................. 36

Fisba Optik AG ........................................... 65

Crystal Systems LLC ................................. 22

Hamamatsu Corporation ............................17

IDEX/Melles Griot ....................................... 11

JDSU ........................................................... 64

LightMachinery, Inc. ............................ 16, 20

Master Bond, Inc. ...................................... 34

Micro Laser Systems, Inc. ................... 28, 63

Moxtek Optics .......................................26, 57

Nanoplus GmbH ..........................................24

Newport Corporation ..................... 21, 29, 65

NM Laser Products, Inc. ............................ 28

Ophir-Spiricon, Inc. .............................. 25, 64

Optical Society of America ........................ 54

Optimax Systems, Inc. .................................4

Opto Diode Corporation ............................. 35

OptoSigma Corporation ..............................12

OSI Optoelectronics ................................... 23

Photonics Consortium ............................... 44

Pico Electronics, Inc. ..................................37

Power Technology Inc. .................................1

Princeton Optronics, Inc. ............................61

Reynard Corporation ..................................47

Santec USA Corp. ...................................... 22

SPIE ...................................................... 30, 50

Stanford Research Systems ..................... C3

Thin Film Center Inc. .............................31, 34

VLOC/Division of II-VI, Inc. ......................... 43

Xi’an Focuslight Technologies Co., Ltd. .... 32

Zygo Corporation ....................................... C2

This ad index is published as a service. The publisher does not assume any liability for errors or omissions.

Send all orders & ad materials to: Ad Services Specialist, Laser Focus World, 1421 S. Sheridan, Tulsa OK 74112

Laser Focus World Copyright 2013 (ISSN 1043-8092) is published 12 times per year, monthly, by PennWell, 1421 S. Sheridan, Tulsa OK 74112. All rights reserved. Periodicals postage paid at Tulsa, OK 74101 and additional mailing offces. Subscription rate in the USA: 1 yr. $162, 2 yr. $310, 3 yr. $443; Canada: 1 yr. $216, 2 yr. $369, 3 yr. $507; International Air: 1 yr. $270, 2 yr. $435, 3 yr. $578. Single copy price: $17 in the USA, $22 in Canada and $27 via International Air. Single copy rate for March issue which contains a Buyers Guide Supplement: $135.00 USA, $168.00 Canada, $200.00 International Air. Digital edition $60.00 yr. Paid subscriptions are accepted prepaid and only in US currency. SUBSCRIPTION INQUIRIES: phone: (847) 559-7520, fax: (847) 291-4816. (POSTMASTER: Send change of address form to Laser Focus World, POB 3425, Northbrook, IL 60065-3425.) Return Undeliverable Canadian Addresses to: P.O. Box 122, Niagara Falls, ON L2E 6S4. We make portions of our subscriber list available to carefully screened companies that offer products and services that may be important for your work. If you do not want to receive those offers and/or information, please let us know by contacting us at List Services, Laser Focus World, 98 Spit Brook Road, LL-1, Nashua, NH 03062.

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Laser Focus World is a registered trademark. All rights reserved. No material may be reprinted. Bulk reprints can be ordered from Katrina Frazer, PennWell, Laser Focus World, 98 Spit Brook Road, LL-1, Nashua, NH 03062, tel. (603) 891-9231; fax. (603) 891-0574, Attn. Reprint Dept.; [email protected].

MAIN OFFICE

98 Spit Brook Road, LL-1, Nashua, NH 03062-5737 (603) 891-0123; fax (603) 891-0574

Senior Vice President & Group Publisher Christine A. Shaw, (603) 891-9178 [email protected]

Sales & Marketing Executive Assistant Patricia Wharton (603) 891-9174; [email protected]

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Ad Services Manager Alison Boyer-Murray (918) 832-9369; fax (918) 831-9153 [email protected]

Director, List Sales Kelli Berry (918) 831-9782; [email protected]

NORTH AMERICA

AL, AR, DE, DC, FL, GA, IN, KY, LA, MD, MI, MS,

MO, NY, NC, NJ, OK, PA, SC, TN, VA, WV, E. Canada

Jeff Nichols, National Sales Manager (413) 442-2526; fax (413) 442-2527 [email protected]

CA, ID, NV, OR, UT, WA, WY, W. Canada

AnneMarie St. John, (949) 489-8015; fax (949) 489-8037 [email protected]

AZ, CT, CO, IA, IL, KS, MA, ME, MN, MT, ND, NE, NH,

NM, OH, RI, SD, TX, VT, WI Katrina Frazer, (603) 891-9231; fax (603) 891-0574 [email protected]

INTERNATIONAL

France, Germany, Austria, Switzerland,

Russian Federation

Holger Gerisch 49-8856-8020228; fax 49-8856-8020231 [email protected]

United Kingdom Jim Ajayi 44-0-1992-656657; [email protected]

Hong Kong/China Adonis Mak 852-2-838-6298; fax 852-2-838-2766 [email protected]

India Rajan Sharma 91-11-686-1113; fax 91-11-686-1112 [email protected]

Israel (Tel Aviv) Dan Aronovic 972-9-899-5813; [email protected]

Japan Masaki Mori 81-3-6721-9890; [email protected]

Taiwan Diana Wei 886-2-2396-5128 ext. 270; fax: 886-2-2396-7816 [email protected]

For all other international sales, please contact: Christine Shaw, Senior VP & Group Publisher (see contact info. above)

1307LFW_67 67 7/3/13 1:51 PM

BusinessForum

MILTON CHANG of Incubic Management was president of Newport and New Focus. He is currently director of mBio Diagnostics and Aurrion; a trustee of Caltech; a member of the SEC Advisory Committee on Small and Emerging Companies; and serves on advisory boards and mentors entrepreneurs. Chang is a Fellow of IEEE, OSA, and LIA. Direct your business, management, and career questions to him at [email protected], and check out his book Toward Entrepreneurship at www.miltonchang.com.

July 2013 www.laserfocusworld.com Laser Focus World 68

Exploiting an unmet demand is a good model for success

M I LT O N C H A N G

With this column, I am beginning a

new series of interviews with inter-

esting scientists and engineers who

have become successful entrepre-

neurs in photonics. My first interview

is with Henry Kapteyn and Margaret

Murnane of KMLabs (Boulder, CO),

which has been named the winner of

the CLEO/Laser Focus World Inno-

vation Award.

Milton Chang: Let us start by briefly

describing your core competencies.

Henry Kapteyn/Margaret Murnane:

We deliver the highest performance ul-

trafast light. It is light with the shortest

pulse widths, with the cleanest, pedes-

tal-free profile—light confined to only

a few optical cycles in duration, focus-

able to near the diffraction limit. Our

cryogenic cooling technology enables

ultrafast amplifiers with unprecedent-

ed high average powers plus high pulse

energy, and also allows for wide, com-

puter-controlled tuning of the pulse rep

rate. Our second core competency is in

using these lasers as the power source

for high-order harmonic upconversion,

providing what is in essence the first

commercial table-top x-ray lasers.

MC: How did the company

get started?

HK/MM: It started when we, as two

young scientists [a husband-and-wife

team], made an unexpected discov-

ery funded by NSF Young Investor

and AFOSR Awards. The dream was

to use ultrafast lasers to create short

bursts of x-rays—fast enough (<10 fs)

to capture the fastest motions in materials and molecules, even at the level of

electrons. KMLabs came into being when other scientists contacted us, because

they wanted the same 10 fs lasers for other applications. So there was a clear

demand for very short laser pulses that was not

met by existing laser companies.

MC: How did you finance the business initially?

HK/MM: We invested $10,000 of our savings as

assistant professors into KMLabs to get it start-

ed—we have not to date taken outside invest-

ment. That allowed us to get a 10 fs laser oscil-

lator business started. Fortunately, we were also

able to have parts made in the machine shop of

a company started by another professor. High-

power ultrafast amplifier systems are much more

capital-intensive. For those, we used orders on hand to get a line of credit from

the bank. Banking relationships are important, given we have to buy parts to

build products that are shipped many months later.

MC: It appears you have done an excellent job in leveraging your research

funding. You have worked all that out with your university?

HK/MM: Yes, we worked hard to either follow or develop correct procedures

to handle disclosures and joint work. This also involves disclosing and having

proper oversight through a conflict-of-interest compliance officer. The univer-

sities own all IP developed by faculty in their area of research, whether devel-

oped by us at JILA [a joint institute of the University of Colorado at Boulder

and the National Institute of Standards and Technology] or at KMLabs. We

really had terrific experiences with all the universities we have been associated

with. Both the University of Michigan and the University of Colorado get roy-

alties from the inventions we made that are now sold by KMLabs.

MC: You were professors without prior business experience. Was either of

your parents in business?

HK/MM: Margret grew up in Ireland and her father was an elementary school

teacher—kindergarten, actually. She had to work to pay for college. My par-

ents emigrated from the Netherlands via Canada and I was born in the Chi-

cago area shortly after they arrived. My father started an continued on page 63

1307LFW_68 68 7/3/13 1:51 PM

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1307LFW_C4 4 7/3/13 1:19 PM