April 18, 2023 CS Dept., LUMS, Lahore

Optical Technology

Dr. Salim TariqDr. Salim Tariq

March 31, 2003 Salim Tariq

Component Perspective

Early 1960sEarly 1960s Laser InventedLaser Invented

1970s1970s Low-loss Optical FiberLow-loss Optical Fiber

1980s1980s Optical AmplifierOptical Amplifier

1990s1990s Dispersion Compensation, MEMs & Amplifier Dispersion Compensation, MEMs & Amplifier

TechnologiesTechnologies

March 31, 2003 Salim Tariq

System Perspective

1970s1970s Single channel systems at 850 nmSingle channel systems at 850 nm

Low data rate, short reachLow data rate, short reach 1980s1980s

Single channel systems at 1300 nmSingle channel systems at 1300 nmHigher data rate, longer reachHigher data rate, longer reach

19901990 WDM & DWDMWDM & DWDM

Multiple channel systems at 1550 nmMultiple channel systems at 1550 nm

March 31, 2003 Salim Tariq

Optical Communication Link

Data

Laser

Fiber

Photodetector

Data

March 31, 2003 Salim Tariq

Network Perspective

1970s1970s Optical links for voice/data transferOptical links for voice/data transfer

1980s1980s Optical layer is a high speed dumb mediumOptical layer is a high speed dumb medium

1990s1990s Upper layers are inefficientUpper layers are inefficient

Optical Layer should become Optical Layer should become INTELLIGENTINTELLIGENT

March 31, 2003 Salim Tariq

Fiber Characteristics & Its Impact Low-loss windowsLow-loss windows

BandwidthBandwidth TechnologyTechnology

850 nm850 nm ~ 50GHz~ 50GHz Single Single ChannelChannel

1300 nm1300 nm > 5,000 GHz> 5,000 GHz WDM or WDM or DWDMDWDM

1550 nm1550 nm > 10,000 GHz> 10,000 GHz WDM or WDM or DWDMDWDM

March 31, 2003 Salim Tariq

Fiber Characteristics & Its Impact DispersionDispersion

DispersionDispersion Data Rate Data Rate per Channelper Channel

850 nm850 nm HighHigh LowLow

1300 nm1300 nm LowestLowest HighestHighest

1550 nm1550 nm LowLow HighHigh

March 31, 2003 Salim Tariq

Graphical Effect of Loss & Dispersion

Loss reduces pulse amplitudeLoss reduces pulse amplitudeLimited reachLimited reach

Dispersion increases pulse widthDispersion increases pulse widthLimited data rateLimited data rate

OutIn

Fiber

March 31, 2003 Salim Tariq

Optical Amplifier & Dispersion Compensation Fibers Optical Amplifiers undo the effect of fiber Optical Amplifiers undo the effect of fiber

lossloss DC Fibers undo the effect of dispersion to DC Fibers undo the effect of dispersion to

some extentsome extent Nonlinear Effects in FiberNonlinear Effects in Fiber

Ultimate system limitationUltimate system limitation Optimization techniques must be usedOptimization techniques must be used

March 31, 2003 Salim Tariq

Laser Technology

SM lasersSM lasersLeast effected by dispersionLeast effected by dispersionSuitable for WDMSuitable for WDM

Tunable SM LasersTunable SM Lasers

~ 100 GHz 0.01 - 0.1 GHz

MM Laser SM Laser

March 31, 2003 Salim Tariq

Tunable SM Lasers

Spectrum is instrument limitedSpectrum is instrument limited

March 31, 2003 Salim Tariq

Capacity of Today’s Links

DWDM technologyDWDM technology 150 channels of 10 Gbps each in a fiber150 channels of 10 Gbps each in a fiber Reach is about 1,000 to 1,500 km Reach is about 1,000 to 1,500 km

• Roughly from Karachi to Peshawar.Roughly from Karachi to Peshawar. No O/E/O conversion needed.No O/E/O conversion needed. How to route the traffic?How to route the traffic?

March 31, 2003 Salim Tariq

Electro-Optical Bottleneck

Bandwidth of electronics ~ 1GHzBandwidth of electronics ~ 1GHz Bandwidth of optical channel ~25GHzBandwidth of optical channel ~25GHz Processing speed limitationProcessing speed limitation

Multi-million gate devices neededMulti-million gate devices needed Optical NonlinearitiesOptical Nonlinearities

Nonlinear response of the fiber Nonlinear response of the fiber materialmaterial

March 31, 2003 Salim Tariq

Optical Networking

Wavelength Add/DropWavelength Add/DropA fixed wavelength is droppedA fixed wavelength is droppedThe same wavelength is addedThe same wavelength is added

Agile NetworkAgile NetworkRemotely reconfigured wavelength Remotely reconfigured wavelength

add/dropadd/drop

• Express channelsExpress channels

March 31, 2003 Salim Tariq

Wavelength Add/Drop

Fixed wavelength is add/dropped at a Fixed wavelength is add/dropped at a predetermined locationpredetermined location

Modification requires hardwiringModification requires hardwiring Electro-optical devicesElectro-optical devices

Drop Add1, 2, 3

3

1, 2

3

1, 2, 3

March 31, 2003 Salim Tariq

Agile Networks

Wavelength add/drop is dynamicWavelength add/drop is dynamic• All optical or electro-opticalAll optical or electro-optical

Drop Add1, 2, 3

3

1, 2

3

1, 2, 3

3:00 am

Drop Add1, 2, 3

2 , 3

1 1, 2, 3

2 , 310:30 am

March 31, 2003 Salim Tariq

Wavelength Routing

Wavelength dependent routingWavelength dependent routingAll optical is desirable for less complexityAll optical is desirable for less complexity

1a, 2a, 3a 1a, 2b, 3c

1b, 2b, 3b

1c, 2c, 3c

1c, 2a, 3b

1b, 2c, 3a

a

b

c

x

y

z

March 31, 2003 Salim Tariq

MEMs Technology

Micro Electro-Mechanical MirrorsMicro Electro-Mechanical MirrorsMirror manufactured on siliconMirror manufactured on siliconMechanically controlledMechanically controlled

March 31, 2003 Salim Tariq

A mirror

Size ~0.1 mm - 1 mm, Gold layer ~.01 Size ~0.1 mm - 1 mm, Gold layer ~.01 mm

MEMS Technology for Optical Networking ApplicationsA. Neukermans, R. Ramswami, IEEE Comm. Mag., Jan 2001

March 31, 2003 Salim Tariq

MEMS Cross-connect

• An Optical Cross-connect (1152 x 1152)

MEMS Technology for Optical Networking ApplicationsA. Neukermans, R. Ramswami, IEEE Comm. Mag., Jan 2001

March 31, 2003 Salim Tariq

MEMs X-Connect for Add/Drop

O/E/O conversion not neededO/E/O conversion not needed

Optical Cross-Connect

Drop Add

Electronic Control

DeMux Mux

March 31, 2003 Salim Tariq