Design and Optimisation of Photonics Devices: Supporting a Key Enabling
Technology
Prof. B. M. A. Rahman,
City, University of London, UK
EngiTek 2020 Congress16th June, 2020, Irbid, Jordan
Evolution of Engineering to ElectronicsEmergence of PhotonicsBecoming a Key Enabling TechnologyOverview of ModellingBriefly some our resultsConclusions
Outline of my talk
Michael Faraday
FRS
in London
1791-1867: 1831 relation between time varying magnetic field and current
Origin of Electrical Engineering
Origin of Electronics
• 1904: Sir John Ambrose Fleming; Vacuum Tube – Diode• Head of EE, University College London
• 1906: Lee De Forest: Triodes
Start of electronics
Sir John Ambrose Fleming
1849-1945: invented electronic valve in 1904
1947: Invention of transistor in Bell Labs –started the revolution of electronics
Rapid Development of Electronics• Electronic valves• Transistors• IC > LSI > VLSI
• This rapid development had profound affect on all aspects of our life in the 20th Century
Moore’s Law
Let’s follow
• Emergence and progress of the Information Technology
James Clerk Maxwell, FRS
1864: Maxwell’s Equations: predicted electromagnetic waves
1887: Henrich Hertz demonstrated experimentally
King’s College, London; Cambridge
• Rapidly followed by the invention of
• Radio in 1897• TV 1927• Phone 1876• Mobile phone 1973• Internet 1969
The
Supported growth of Internet Dec 08: 1.5 billion users
Growth 1000% during last 20 years
In 2019 4.5 Billion Internet users out of 7.7 B populations
Global Internet traffic
2G 3G 4G 5G
DATA VOLUME1000x mobile data
CONNECTED DEVICES10x - 100x
~5x LOWER LATENCY
HIGH END-USER DATA RATES10x – 100x
10x POWER SAVINGFor low powered devicesSource: METIS
We talked about revolution of electronics and continuous progress of communication technologies
What role can the photonics play here?
What is Photonics?
Electronics manipulates Electrons
but Photonics manipulates photons or light
Emergence of Photonics in 1960s• Semiconductor lasers• Optical Fibres
Nobel prize 1964
• Townes, Basov and Prokhorov (from the Soviet Union) won the Nobel Prize in 1964 for their work on both microwave and optical lasers
• Schawlow won the Nobel prize in 1979 for work on laser spectroscopy
Nobel prize in 2009
Optical fibre development
• Concept of modern clad optical fibre developed by Kao and Hockham in the UK at STL in 1966
• Presented at IEE in January 1966• Identified 1000 dB/km loss due to impurities
• By 1970 Corning reported loss reduced to 20 dB/km
Photonics
• Most of the major inventions were from the need of telecommunication sectors
• Most of the market is related to consumer products
New communication systems
FLAG Pacific -1: 22000 km, 8 pairs of fibres
Each fibre WDM 64 λ @ 10 Gb/s = 5 Tb/sec
= 60 million simultaneous telephone channels
Optical communication is a part of Photonics
Impact of Photonics• Telecommunications• Appliances: CD/DVD Players, Display, scanner,
Laser printers, illuminations • Industrial uses: material processing• Medical applications, corneal sculpting• Sensing: physical, chemical, biological
But now big market is consumer products such asToday: Photonics for storage & retrieval
Storage 25 GB Blue Ray DVD
Today: Photonics for Display
New Flat Screen TV, New Flat Screen TV, HD or UHD (4k = 3840x2160 pixels)
also screen for mobile phones
Photonics for printing
Today’s colour laser printer
Laser in healthcare
LASIK: Vision correction
Ultraviolet Excimer laser for eye surgery
Photonic for illuminations
More efficient than incandescent or fluorescent lights
Optical sensors: a massive market
Optical pressure sensor
There can be 200 sensors in a car
Laser in material processing
The University for businessand the professions
Car and plane’s body parts are processing by high power lasers
Stents are fabricated by high power lasers
Photonics
• Horizon 2020 EU Research Programme
• Photonics – A Key Enabling Technology (KET)
Photonics technology: The pillars
• Materials• Devices• Systems
• Exploitations
Photonic Devices Work at City University
Various types of Optical Waveguides
Optical Modulators, 3dB couplers, MxNsplitters, filters, Bragg gratings, Spot-size converters, Compact bends, Nonlinear Devices, VCSELs, Polarization Splitters, Polarization Rotators, Polarization Controllers, etc.
For my contribution over last 41 years is the developing finite element based numerical modelling tools for photonic devices
• Fellow of IEEE • Fellow of OSA• Fellow of SPIE
Types of Photonic Devices
• Uniform Optical Waveguides: Modal Solutions
• Nonuniform Guided-wave structures• Butt-coupled uniform sections• Junction Analysis• Arbitrarily nonuniform structures• Beam Propagation Methods
• Time-domain approaches
Uniform in z-direction: n(x,y)Find modal field E(x,y) or H(x,y) and γ = α + j β
Optical waveguides are key components
Modal solutions for optical waveguides
• Semi-analytical approach• Effective Index Method • Numerical approaches• Fourier-based method : Spectral Index Method• Finite difference method• Finite element method• Transfer Matrix method• Beam Propagation Method•
Finite Element Method (FEM)
• Structural problems• Fluid dynamics• Thermodynamics• Electromagnetics
• Electrical machine designs• Radio frequency, microwave• Optical waveguides & Devices
DiscretizationIn the FEM the structural cross-section is
subdivided into a finite number of elements.
Discretisation
In the FEM the waveguide cross-section (x,y) is subdivided into a finite number of elements.
Any structure can be represented
element
The Variational Formulation
( ) ( ) ( ) ( )
∫
∫∫Ω⋅⋅
Ω⋅⋅∇⋅∇
+Ω×∇⋅×∇
=
−
dHH
dHHdHH
µεαε
ωˆ
)ˆ
*
*
0
1*
2
IEEE JLT p.682, 1984
Full Vectorial
Naturally satisfies boundary conditions
Exact-in-the-limit
Valid for general anisotropic refractive index
Citations: 1400+
Discontinuity AnalysisMisalignment
Directional Coupler
MMI
Butt-coupled uniform sectionsTo obtain modal coefficients: needs junction analysis
Least Squares Boundary Residual method
The energy functional J is given by
J E E Z H H dtI
tII
tI
tII= − + ⋅ −∫
202
2α
Ω
Ω
Continuity of Et and Ht is enforced
IEEE JLT p.52, 1988
Cited 120+ times
Beam Propagation Method
essential for z-variantn(x,y,z) type of structures
• Fourier, FDM or FEM-based• Scalar, Semivectorial, or Vectorial formulation• ABC, TBC, PML Boundary condition
• H-field based: JLT 2000 paper cited 140+ times
Time-domain approach
• FDTD• Valid for general electromagnetic problems• Particularly useful for pulse propagation, strong
discontinuities (photonic crystals, nanoparticles) and strong nonlinearity
• Computationally very versatile but computer intensive as being 4-dimesnional (x,y,z,t)• Often approximation is used to reduce 1D• Poor in representing very fine features• Poor in representing curved/slanted surfaces
Needs and emerging areas of research in photonics
• Higher data rate for communications
• Silicon photonics
• Plasmonics
• Nonlinear Photonics
• Bio-Photonics
• Metamaterials
The University for businessand the professionsWaveguide: after optical fibre > Photonic Crystal Fibre
First reported by Prof. Philip Russel, Univ Bath, England
Single material
Low loss
Adjustable spot size
Endlessly single mode (nearly)
Adjustable GVD
A 2-D, Hx contour field, for the Hx11 mode
-4 -3 -2 -1 0 1 2 3 4-4
-3
-2
-1
0
1
2
3
4
Air Holes
Defect Region
Transmission Capacity in Optical Fibers
Fig. The evolution of transmission capacity in optical fibers due to technological breakthroughs.*
*White Paper (2013) “Space Division Multiplexing: A new milestone in the evolution of fiber optic communication,” Nokia Siemens Networks, http://modegap.eu/?p=767. 52
Data demand increasing rapidly and continuously
• WDM
• Polarisation division multiplexing
• Space division multiplexing
• Vortex modes?
8-Core MCF InterconnectΛ = core to core pitch
2Λ= distance between the two rows
r1 = core radius
r2 = distance between the center of core and the inner edge of trench
r3 = distance between the center ofcore and the outer edge of trench
Δ1 = relative refractive-index differencebetween core and cladding
Δ2 = relative refractive-index differencebetween trench and cladding
W = width of the trench layer Fig. Schematics of (a) 8-core MCF and (b) trench-assisted index profile.
4
Results and Discussion Contd…
Fig. Variations of mode coupling coefficientand coupling length with the core to corepitch for an 8-core TA-MCF, for differentΔ2, when r2/r1=2.0, r3/r1=3.0, and W/r1=1.0
Fig. Variations of crosstalk with core tocore pitch for an 8-core TA-MCF, fordifferent Δ2 values.
5
IEEE PJ 2017
Multicore Fiber (MCF)
Crosstalk is a potential disadvantage of MCF
Fig. Schematic of MCFs (a)homogeneous MCF* (b) heterogeneousMCF# (c) trench-assisted MCF* and (d)hole-assisted MCF$.*
56
Results and Discussion Contd…
Fig. HY field of the fundamental mode for 8-core step index and TA-MCF, when r2/r1= 2.0, r3/r1= 3.0, and W/r1= 1.0.
Fig. Variation of coupling length and crosstalk with the r2/r1 for 8-core TA-
MCF OI, when r1 = 4.45 μm, Δ1 = 0.35%, Λ = 45 μm, and W/r1= 1.0.
7
Opt Lett. 2015, IEEE Pj 2016, Opt Comm 2016
Mode splitter for mode division multiplexing
• Important device for multimode transmission systems
H𝑦𝑦11
H𝑦𝑦11
H𝑦𝑦11
H𝑦𝑦11, H𝑦𝑦
21 H𝑦𝑦11, H𝑦𝑦
21, H𝑦𝑦31
SiO2
Air Si Si
S
WMWS
H
Asymmetric Directional Coupler
JLT May 2016
Also in OSA Continuum 2019
SHG, supercontinuum sources
• SHG in LiNbO3 in 1997
• SHG in GaAs in GaAs 2000
• SHG in ZnO in 2013
• Four wave mixing in PCF Opt Lett May 2015, • THz generation by FWM: IEEE STQE Inv paper Apr 2016,
and IEEE PTL Aug 2016 issue
Opt Exp Dec 14 and May 15Cover page IEEE QE April2017
Pump wavelength 2.0 µm
Black-solid line curve represents the SCspectrum for the waveguide containingGe11.5As24S64.5 glass for its lower claddingand red-dashed line curve represents thespectrum for the structure employingMgF2 as its lower cladding.
Spectral evolution with a peak power of 500 Wfor (a) air-clad all-chalcogenide waveguide; (b)air-clad chalcogenide core employing MgF2for its lower cladding.
JOSA B Nov 2015, Feb 2018, JAP 2018, PTL Nov 2017, A0 June 2020Cited more than
210+ time
Electronics vs Photonics
• The electronics revolution has been possible with the invention of transistor in 1947 and followed by their integration to IC → LSI → VLSI
• But for photonics, this integration is still in the early stage
• But why?
But so far integration of photonics components have been modest
So far Best in Photonics
• Best waveguides: lowest loss – silica fibres 0.2 dB/km• Best lasers: InP based• Best modulators: Lithium Niobate – but too long• Detectors: Ge• Isolator?? YIG? Not yet integrated!
• As there is not a single material which is good or reasonably good for all the functions, integration of the functions have been poor.
• What about silicon?
Silicon
• Best material for electronics• Heavy investments from semiconductor industries• Well developed CMOS foundry• Low cost, super precisions• Wonder material for electronics
• But is it good for photonics?
Silicon Photonic Waveguides
• Use of well developed Si CMOS Processing Technologies for electronics
• Compact waveguides and devices• Compact bends (< 5 µm) and systems
• Which will allow more components in a chip• Yield is much better• More functionality• More reliable, lower cost • Also can put electronics and photonics together
Silicon Strip Nanowire
Silicon n = 3.45
SiO2 n = 1.45
Silicon n = 3.45
Si Substrate
SiO2 Buffer Layer
3 μm
1.5 μm
260 nm
Width
Air / SiO2
Variations of Hy along X-axis and Y-axis for the Hy11 mode
Variations of the Ex field along the X and Y-axes for the Hy
11 mode
Optics Express 2010
Poly-Si Layers L
SiO2
Si
Poly-Si
h
sp
sH
w1
w2
Cross-section of the SSC
Schematic diagram of the multilayersbased spot-size converter
Schematic diagram of the SSC
Schematic of polarization-independent SSC based on the multi-layer. (a) Schematicdiagram for coupling process; (b) Cross-section of the multi-layer structure.
Scientific Reports, 2020
Example: Silicon Slot Waveguide
A coupled structure where individual guide cannot support a mode but together they can support only one supermode
Contour plot of Ey field for Hx11 mode
Horizontal slot as bio-sensor
Optimization of sensor designs
JLT May 2015
Sensing arm
Reference arm
Gas chamberInlet Outlet
LASER Optical detection
MZI
Wav
egui
de cr
oss-
sect
ion
𝑯𝑯𝒙𝒙− 𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇
𝑬𝑬𝒚𝒚− 𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇
Fast data transfer in computer• Rack-to-rack optical interconnection• Chip-to-chip• On-chip optical signal processing
• Use optical fibre for rack-to-rack• Use silicon nanowires for intra-chip
• Consider electronics and photonics on the same Si chip
GST – fabricated by Shanghai Jiao Tong University, China
GST – IEEE Photonics J Feb 2018
Global energy consumption
Illuminations
Also helps in fighting Global warming
Global electricity consumptions
Google data centre
Energy consumption of a data centre
• Google’s Joe Kava & Heather Dooley Data Centre• Energy consumption in 2015 was 5.7 TWhr
• Where power is consumed in a data centre?• 50% power consumed in transferring data from CPU to
memory through fine gold wire connectors
Power consumptions
• Global data centres consumes 416,000 GW• 3% of whole world’s electricity consumption
• 50-60% consumes in the gold wires transferring data in the processors
• By using optical waveguides, rack-to-rack, chip-to-chip or intra-chip data transfer this can be reduced
Global electricity generation
Pioneer in Renewable energy: solar cells
• Sun is source of all energy sources
• Including fossil fuel, hydro, or wind
• But, we can convert solar energy directly
• Silicon solar cells is the dominant technology now
• Research continuing to increase the efficiency and lower cost
A simple low-index contrast silica waveguide
Displacement vector profiles (a) UX, (b) UY and (c) UZ components of UX11
(a)
(b)
(c)
Ux1,1
Uy2,2
Uz2,1
JOSA May 2016
And effect of higher frequencyIEEE QE 2015
Photonics
• Support rapid data demanded by 5G, IoT,
• Support increased data rate using SDM, MDM
• Rack-to-rack to chip-to-chip data transfer by photonics
• Support lower power consumptions by data centre
• Combine photonics and electronics on one chip
• Reduce global warming through use of better solar cells
• Its uses in healthcare, industrial, consumer products
Conclusions
• At City, University of London, we have one of the strongest research groups in the world on Photonics Modelling.
• Today, I have briefly discussed the emergence, development of Photonics and particularly its ability to shape the future associated technology.
• Thanks to the organiser for arranging my talk.
• But missed to opportunity to visit Jordan – may be next time.