Fort Worth Seminar 2001 - Trafficware Group Inc. · 1.40 1.60 1.80 2.00 Vacuum Air Water Fused Glass Fused Glass Material The ratio of the speed of light in a vacuum to the speed

Fiber Optics

Jim SlussUniversity of Oklahoma

Electrical & Computer Engineeringsluss@ou.edu

Outline

• Part 1: Fiber Basics• Part 2: Fiber Optic Networks for Traffic and

Transportation Systems• Part 3: Troubleshooting

(Problems, Test & Measurement)

Part 1: Fiber Basics

Basic Communications Link

ChannelSource Transmitter Receiver Destination

Noise Interference

Basic Fiber Transmission Link

DriveCircuit

SignalRestorer

LightSource

AmpPhoto-detector

Transmitter Channel Receiver

Electrical OutputSignal

Electrical InputSignal

Attenuation Distortion

Rays of Light Photons

Light is Oscillating Electromagnetic Energy

Smallest Particle of light is called a Photon

A Photon is a quantum or bundle of energy

Only exists if the particle is in motion

Electromagnetic EnergyElectromagnetic Energy

Electromagnetic EnergyElectromagnetic EnergyMagnetic

Electric Field

Direction of Propagation

Travels through free space @ 300,000 Km/sec or 186,000 Miles/sec

Consists of Oscillating Electric and Magnetic Waves at right angles to each other

In free space the Velocity of an Electromagnetic Wave is the Speed of Light 300,000 Km/sec

Wavelength

Sine-Wave

Frequency (Hertz’s) = The number of Cycles/sec

WavelengthWavelength (Meters) = (Meters) = The distance between the same points on consecutive waves

Positive AmplitudeNegative Amplitude

Electromagnetic Waves are Sinusoidal in shape

Electric Field

In free space the velocity of an Electromagnetic Wave is the Speed of Light 300,000 Km/sec

Wavelength

Sine-Wave

Wavelength =Velocity

FrequencyWavelength = Meters

Velocity = 300,000Km/Sec.

Frequency = Hertz

What is the wavelength of 60 Hz ?

Wavelength = 300,000 Km 60 Hz

= 5000Km

Los Angeles Boston5000 Km

QuestionQuestion

Electric Field

In free space the velocity of an Electromagnetic Wave is the Speed of Light 300,000 Km/sec

Wavelength

Sine-Wave

Wavelength =Velocity

FrequencyWavelength = Meters

Velocity = 300,000Km/Sec.

Frequency = Hertz

QuestionQuestionWhat is the wavelength of 2.4 GHz ?

Wavelength = 300,000 Km 2.4 GHz

= 125 microns

Approximately the same diameter as a strand of human hair!

100 Sub-sonic

(1 MHz) 10 6 AM Radio

10 410 5

(1 KHz) 10 3 Sound10 2

(1 THz) 10 12

(1 GHz) 10 9Radar

Television

Short-wave RadioFM Radio

10 1010 11

10 16Ultraviolet Rays

Visible LightInfrared Light10 13

Cosmic Rays

Gamma Rays

X-Rays

Electromagnetic SpectrumElectromagnetic SpectrumHigh Frequency

Ultra- Short Wavelengths

Low Frequency

Long Wavelengths

18K Hertz

20 Hertz

Ultra Violet

Violet

Yellow

Orange

Infrared

850Far Infrared

Wavelength (nm)

Electromagnetic SpectrumElectromagnetic Spectrum

Violet Blue Green Yellow Orange RedUltra-Violet Infrared

Invisible Light

400 455 490 550 580 620 750 800

Wavelength (nm)

10 – 9 m

1,000,000,000

850 1300 1550

Visible Light

Fiber Optics Transmission

The Speed Of LightThe Speed Of Light

1 1.0003

1.331.46 1.48

0.000.200.400.600.801.001.201.401.601.802.00

Vacuum Air Water FusedGlass

FusedGlass

Material

The ratio of the speed of light in a vacuum to the speed of light in a specific medium

CoreCladding

Index of Refraction

Velocity

300,000 Km/s

205,000 Km/s

225,000 Km/s

Journey of LightJourney of Light

InterfaceInterface

GlassGlassI.O.RI.O.R1.481.48

I.O.RI.O.R1.461.46

Angle ofAngle ofIncidence Incidence

RayRay

Refracted Refracted RayRay

NormalNormal

Angle ofAngle ofIncidence Incidence

RayRay

Angle ofAngle ofRefractionRefraction

CriticalCriticalAngleAngle

Angle ofAngle ofIncidenceIncidence == Angle ofAngle of

ReflectionReflection

Advantages of Optical FiberAdvantages of Optical Fiber••Wide Bandwidth Wide Bandwidth

••Low Loss Low Loss

••Electromagnetic Immunity Electromagnetic Immunity

••Light Weight Light Weight

••Small Size Small Size

••Safety Safety

••Security Security

Flat OC192 129,024 Voice ChannelsFlat OC192 129,024 Voice Channels

Fiber is Dielectric, does not carry electricityFiber is Dielectric, does not carry electricity

0.25dB/Km @ 1550nm0.25dB/Km @ 1550nm

Optical FiberOptical FiberTwo Types Of Fiber -

MultimodeMultimode

SinglemodeSinglemode

• Used for Low Bandwidth (less than 650MHz), Short Haul Communications with distances of up to 3Km (850nm) & 10Km (1300nm)

• Two operating wavelengths, 850nm and 1300nm

• Used for High Bandwidth, Long Haul Communications with distances of up to 40Km (1310nm) and 100Km (1550nm) or more

• Two operating wavelengths at 1310nm and 1550nm

MMultimode & Singlemodeultimode & Singlemode

125 / 62.5 125 / 62.5 micronsmicrons

MultimodeMultimode

CoreCore

FiberFiberBufferBuffer

CladdingCladding

Core / Cladding sizes 50/125, 62.5/125 and 100/140 microns

FDDIFiber Distributed Data Interface

WavelengthWavelength

850 & 1300nm850 & 1300nm

FiberFiberBufferBuffer

125 / 125 / 9/ 9micronsmicrons

CladdingCladdingCoreCore125 / 125 / 99/

9micronsmicrons

Core less than 10 microns Cladding 125 micronsWavelengthWavelength

1310 & 1550nm1310 & 1550nm

Attenuation vs. λ

MultimodeMultimode

Refractive Index Profiles

• Multimode Stepped Index Fiber

• Multimode Graded Index Fiber

• Singlemode Stepped Index Fiber

Mode Time Scale

Multimode Stepped Index Fiber

ModalModal

Input Input Output Output Bandwidth Limited to about Bandwidth Limited to about

150Mhz/Km 150Mhz/Km Refractive Refractive

Index Profile Index Profile

Core 100 microns

Cladding 140 microns

Mode Time Scale

Multimode Graded Index Fiber

ModalModalRefractive Refractive

Index Profile Index Profile

Input Input Output Output Bandwidth Limited to Bandwidth Limited to

about 650Mhz/Km about 650Mhz/Km

Signal DistortionImportant in determining the information capacity (bandwidth) of an optical fiber as a function of transmission distance.

Intermodal DispersionIntermodal dispersion - pulse spreading (in time) in multimode fibers, due to varying arrival times at the RX because each mode travels with a slightly different velocity.

cladding

mode 1

mode 2

Axial Cross-Sectio

Refractive Refractive Index Profile Index Profile

Stepped Index, Terahertz Bandwidth Stepped Index, Terahertz Bandwidth

Singlemode Step Index Fiber

Dynamic Range Dynamic Range

Wavelength / Attenuation Wavelength / Attenuation

850nm 850nm

1300nm 1300nm

1310nm 1310nm

1550nm 1550nm

Multimode Multimode

3.5dB/Km3.5dB/Km

1.75dB/Km1.75dB/Km

0.5dB/Km0.5dB/Km30 Km30 Km

60 Km60 Km

8.75 Km8.75 Km

0.25dB/Km0.25dB/Km

/ Distance / Distance

=15dB=15dB

P0 P0 --15dBm15dBm

4.28 Km4.28 Km

LDL LDL --30dBm 30dBm

BER 1x10BER 1x10 66--

Wavelength / Attenuation / Bandwidth Wavelength / Attenuation / Bandwidth

1310nm 1310nm

1550nm 1550nm

SinglemodeSinglemode0.5dB/Km0.5dB/Km

0.25dB/Km0.25dB/Km

UnlimitedUnlimited

850nm 850nm

1300nm 1300nm

Multimode Multimode 3.5dB/Km3.5dB/Km

1.75dB/Km1.75dB/Km650 MHz/Km650 MHz/Km

100 MHz/Km100 MHz/Km

Four Operating Wavelengths Four Operating Wavelengths Four Operating Wavelengths

1310nm1310nmSinglemodeSinglemode

850nm850nm1300nm1300nm

1550nm1550nm

MultimodeMultimode LED’sLED’s

ELED’s

LASER’s

ELED’s

LASER’s

Fiber Cables

Point-to-Point Digital Transmission Links

• Link Requirements:– Transmission Distance– Data Rate or Bandwidth

A designer has the choice of the following:

1) Fiber -Multimode or single-modeCore size and refractive index profileAttenuationNumerical aperture

2) Source -Laser diode or LEDEmission Spectral widthOutput powerSpeed (bandwidth)Effective emitting areaEmission pattern

3) Detector –Sensitivity (or responsivity)Speed (bandwidth)Operating λ

Link Power Budget Analysis

PS - PR ≥ [ αf L + m(lc) + n(lsp) + system margin ]

where αf = fiber attenuation (dB/km)L = fiber length (km)m = number of connectorslc = loss per connector (dB)n = number of spliceslsp = loss per splice (dB)PS = source output power (dBm)PR = receiver sensitivity (dBm)

System Margin

• System margin is typically specified at 6 to 8 dB to allow for new components, component aging, and temperature fluctuations.

Link Rise Time Budget

• One accepted method for determining the dispersion limitiation of a fiber optic transmission system is to calculate the system rise time, tsys, and ensure that it does not exceed 70% of the NRZ bit period.

tsys = [ ( ttx)2 + ( tGVD)2 + ( tmod)2 + ( trx)2 ]1/2

Signal Coding

where ttx = transmitter rise time (spec'd by manufacturer)

tmat = material dispersion rise time = DσλLor

tGVD = group-velocity dispersion ≈ |D|Lσλwhere D = material dispersion

σλ = source spectral widthL = fiber length

tmod = modal rise time 0 for single-mode fibertrx = receiver rise time (spec'd by

manufacturer)

Exercise

A 1550 nm single-mode digital fiber optic link needs to operate at 622 Mb/s over 80 km without amplifiers. A single-mode InGaAsP laser launches an average optical power of 0 dBm into the fiber. The fiber has a loss of 0.25 dB/km, and there is a splice with a loss of 0.1 dB every km. The coupling loss at the receiver is 0.5 dB, and the receiver uses an InGaAs APD with a sensitivity of –39 dBm.

a) Find the system margin.b) Find the system margin at 2.5 Gb/s with an APD

sensitivity of –31 dBm.

SolutionPS - PR ≥ [ αf L + m(lc) + n(lsp) + system margin ]

so we can calculate the system margin fromsystem margin ≤ PS - PR - αf L - m(lc) - n(lsp)

where PS = 0 dBmαf = 0.25 dB/kmL = 80 kmm = 1lc = 0.5 dBn = 79lsp = 0.1 dB

Solution (continued)a) PR = –39 dBm for a data rate of 622 Mb/ssystem margin ≤ 0 dBm – (-39 dBm) – (0.25 dB/km)(80 km)

– (1)(0.5 dB) – (79)(0.1 dB)system margin ≤ 10.6 dB, which is very respectable

b) PR = –31 dBm for a data rate of 2.5 Gb/ssystem margin ≤ 0 dBm – (-31 dBm) – (0.25 dB/km)(80 km)

– (1)(0.5 dB) – (79)(0.1 dB)system margin ≤ 2.6 dB, which is really not good enough to

ensure long-term, problem-free operation of the link

ExerciseYou are assisting with the design of an OC-192 fiber

optic transmission link. Given a 1550 nm laser diode with a rise time of 25 ps and a spectral width of 0.1 nm, and a receiver with a rise time of 25 ps:

a) Determine the maximum dispersion-limited transmission distance through a fiber optimized for a 1310 nm source (assume a material dispersion of 15 ps/nm-km).

b) Determine the maximum dispersion-limited transmission distance through a dispersion-shifted fiber optimized for a 1550 nm source (assume a material dispersion of 2 ps/nm-km).

Solution

( ) ( ) ( ) ( )

12 2 2 2 2

12 22 2 2

substituting for

and solving for

sys tx GVD rx

sys tx rx

t t t t t

t t D L t t

t t t tL

= + + + =

= + + +

− − − =

Solution (continued)From the problem statement,

ttx = 25 pstmod ≈ 0trx = 25 psσλ = 0.1 nm

For an OC-192, the data rate is approximately 10 Gb/s, so the NRZ bit period isTb= 1x10-10 s = 100 ps. Thus, tsys should not exceed 70% of Tb, so set tsys=70 ps.

Solution (continued)

( ) ( ) ( )( )( )

12 2 2 2

a) transmission through a fiber optimized for a 1310 nm source with 15 / .

70 25 25

15 / 0.1

b) transmission through a dispersion-shifted fiberoptimized for

D ps nm km

ps ps psL

ps nm km nm

− − =⋅

( ) ( ) ( )( )( )

12 2 2 2

a 1550 nm source with 2 / - .

70 25 25

2 / 0.1

302.08

D ps nm km

ps ps psL

ps nm km nm

− − =⋅

End of Part 1

Fiber Optic Networks for Traffic and Transportation Systems

Part 2

CommonCommunication Network

InfrastructureMediums (Wire, Wireless, Fiber)

Field MastersBridges, Routers, Multiplexers, Cross-Connects

Infrastructure Interfaces

SignalSystem

RampMetering

VideoControl

Sensors

Environ-mental

RuralSuburbanUrbanFreeway/Metropolitan

CountyStateNationalPrivateServices

Other StateAgencies

ITS Communication Interface Concept

NTCIP-CompatibleField Interfaces

& Protocols

TMCInterfaces

ExternalInterfaces

Advantages:Share DataTMC BackupShared External InterfacesReduced Comms Costs

Agency Options

• Install-Operate-Maintain• Lease• Public/Private Partnerships

Network Requirements

• Data - Signal systems, VMS, video PTZ, vehicle detectors, sensors, etc.

• Voice - Craft interfaces, HAR, emergency call boxes.

• Video - Incident monitoring, surveillance, video detection.

Analog vs. Digital Video? The answer drives required network bandwidth.

MultiplexingMultiplexing

Multiplexing De-Multiplexing

DATADATADATA

LANLANLAN

PLCPLCPLC

VOICEVOICEVOICE

DATADATADATA

LANLANLAN

PLCPLCPLC

VOICEVOICEVOICE

Separates out the Input Signals from the Composite to form Corresponding Outputs

Combines Two or More Signals into a Composite Signal for Transmission

MultiplexingMultiplexing

Network TopologiesStar Ring

Linear

Fault-Tolerant Ring Topologies

PrimaryData Path

SecondaryData Path

Fiber Cut

Typical Fiber Network Application

SONETNODE

RS-232

Modem Controller

ModemConnections

Sensors

Interconnect DiagramInterconnect Diagram

Hybrid Fiber/Wireless Network

SONETNODE

ProtocolInterface

Controller ProtocolInterface

Controller

Radio Controller

ProtocolInterface

Antenna

RS-232

Radio Controller

Antenna

Sensors

SONETSynchronous Optical Network

SONETLevel

(optical)

SONETLevel

(electrical)

Line Rate(Mb/s)

SDHLevel

OC-1 STS-1 51.84 STM-0OC-3 STS-3 155.52 STM-1OC-12 STS-12 622.08 STM-4OC-24 STS-24 1,244.16 STM-8OC-36 STS-36 1,866.24 STM-12OC-48 STS-48 2,488.32 STM-16

OC-192 STS-192 9,953.28 STM-64

OC - Optical Carrier STS - Synchronous Transport Signal STM - Synchronous Transport Module

OC - 1

OC - 1OC - 1

OC - 1

OC - 3

OC - 3 OC - 12

OC - 12

OC - 48

OC - 192

SONET Multiplexing

SONET NetworkingSuper Capacity

(WDM)OC-192 OC-192

High Capacity(WDM)

SuperCapacity

LowCapacity

HighCapacity

OC-192OC-192OC-48

OC- 48 OC- 48

OC- 48

OC-12OC-12OC - 3

OC - 3OC - 3OC - 3

OC - 3OC - 3

Super - ExpressLayer

ExpressLayer

AccessLayer

OC-192OC-192

Transmission Over SONET

• PCM Digital Hierarchy• ATM Over SONET• Packet Over SONET (POS) or IP over

Wavelength Division Multiplexing (WDM)

1300 nm

1550 nm

WDM1550 nm

1300 nm

WDM 1550 nm

1300 nm

WDM 1550 nm

1300 nm

Dense WDM (DWDM)

(demux)

Optical Transport Network (OTN) G.709

• For data rates of 10 Gb/s and above, optical transmission lengths decreaseOTN uses Forward Error Correction (FEC) to increase optical link distance

• Need to transport a wide range of servicesOTN offers flexible payload management with minimum additional overhead

Optical Transport Network (OTN) G.709

• Minimize O/E/O conversionsEnd-to-end transport of optical channels without O/E/O conversions

• Ability to manage emerging DWDM networksOTN offers management capabilities in the optical domain

Optical Transport Network

PhotonicTransport

Router

BackboneIP Router

PhotonicTransport

Router

DWDM Link

Photonic Transport Node

Virtual Photonic CoreTransport Network

(no electrical terminations)

End of Part 2

Part 3Part 3

Troubleshooting ProblemsTroubleshooting Problems

Test & MeasurementTest & Measurement

ProblemsProblems

Typical Problems

Low Levels

RXTXFiber Optic Cable

Dirty Connectors

Connectors not seated properly

Pinched Fibers

Tight bending radius’s

Bad Patchcords

Patchcord Patchcord

Low Transmit Levels

Ferrule Must be Clean

Key/Keyway must be engaged in mating

hardware

Avoid Tight Bending Radius’s

Avoid Stress Points Tie wrap Cinched Tight,

Must be Loose

ProblemsProblems

Typical Problems

High Levels

Not enough Loss in Fiber Plant

Patchcord Patchcord

High Transmit Levels (LASER) Fixed Attenuator

Barrel Type Variable Attenuator

Screw adjustable Attenuator

5db increments

3 to 30db

Attenuators

ProblemsProblems

Typical Problems

No Receive Level

Dirty Connectors

Connectors not seated properly

Bad Patchcord (Open)

No Transmit Output

Wrong Fiber

Patchcord Patchcord

Ferrule Must be Clean

Key/Keyway must be engaged in mating

hardware

Avoid Tight Bending Radius’s

Avoid Stress Points Tie wrap Cinched Tight,

Must be Loose

Optical Loss Measurements

Patchcord PatchcordBulkhead

Connection

Power MeterLight Source

Reference Measurement

Relative Reference Measurement

-15.0dBmRef-0.00dBm850nm

850nmReceived Level

Patchcord Patchcord

Bulkhead Connection

Power MeterLight Source

Attenuation Measurement ---Forward Direction

-5.00dBm

Bulkhead Connection

Fiber under test

Fiber Loss

Patchcord Patchcord

Bulkhead Connection

Power Meter Light Source

Attenuation Measurement ---Reverse Direction

-4.80dBm

Bulkhead Connection

Fiber under test

Fiber Loss850nm

Recording the Results

BA LossAB LossFiber Cable #

OTDR Measurements

OTDR DEAD ZONES

Near End or

Attenuation DZ Splice DZ

Connector DZ

End of Cable

OTDR Measurements

Splice Loss

LSA Two Point

Distance between Markers Km

dB Loss

Distance between Markers Km

OTDR Measurements----

Optical Return Loss

Large Reflection

Small Reflection

Cleave Fiber -14.5db

Flat Finish -14.5db

PC Finish - 45db

Dirty Connectors also cause Reflections

Increases Bit Error Rates

Increases Noise in Analog Systems

Optical Return Loss ---- Problems with Reflections

Set up an Electronic Data Base

Fiber Characterization

• Record losses for all useable wavelengths

• Bi- Directional Loss Measurements

• OTDR traces for 850 / 1300nm Multimode and 1310 / 1550nm Singlemode

• Bi- Directional traces for each fiber

End of Part 3

Fort Worth Seminar 2001 - Trafficware Group Inc. · 1.40 1.60 1.80 2.00 Vacuum Air Water Fused Glass Fused Glass Material The ratio of the speed of light in a vacuum to the speed

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