Optical Technology

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Optical Technology

• Dr. Salim Tariq

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Component Perspective

• Early 1960s
• Laser Invented
• 1970s
• Low-loss Optical Fiber
• 1980s
• Optical Amplifier
• 1990s
• Dispersion Compensation, MEMs Amplifier
  Technologies

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System Perspective

• 1970s
• Single channel systems at 850 nm
• Low data rate, short reach
• 1980s
• Single channel systems at 1300 nm
• Higher data rate, longer reach
• 1990
• WDM DWDM
• Multiple channel systems at 1550 nm

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Optical Communication Link
Photodetector
Laser
Data
Fiber
Data
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Network Perspective

• 1970s
• Optical links for voice/data transfer
• 1980s
• Optical layer is a high speed dumb medium
• 1990s
• Upper layers are inefficient
• Optical Layer should become INTELLIGENT

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Fiber Characteristics Its Impact

• Low-loss windows

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Fiber Characteristics Its Impact

• Dispersion

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Graphical Effect of Loss Dispersion
Fiber

• Loss reduces pulse amplitude
• Limited reach
• Dispersion increases pulse width
• Limited data rate

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Optical Amplifier Dispersion Compensation Fibers

• Optical Amplifiers undo the effect of fiber loss
• DC Fibers undo the effect of dispersion to some
  extent
• Nonlinear Effects in Fiber
• Ultimate system limitation
• Optimization techniques must be used

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Laser Technology
MM Laser
SM Laser
0.01 - 0.1 GHz
100 GHz

• SM lasers
• Least effected by dispersion
• Suitable for WDM
• Tunable SM Lasers

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Tunable SM Lasers

• Spectrum is instrument limited

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Capacity of Todays Links

• DWDM technology
• 150 channels of 10 Gbps each in a fiber
• Reach is about 1,000 to 1,500 km
• Roughly from Karachi to Peshawar.
• No O/E/O conversion needed.
• How to route the traffic?

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Electro-Optical Bottleneck

• Bandwidth of electronics 1GHz
• Bandwidth of optical channel 25GHz
• Processing speed limitation
• Multi-million gate devices needed
• Optical Nonlinearities
• Nonlinear response of the fiber material

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Optical Networking

• Wavelength Add/Drop
• A fixed wavelength is dropped
• The same wavelength is added
• Agile Network
• Remotely reconfigured wavelength add/drop
• Express channels

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Wavelength Add/Drop

• Fixed wavelength is add/dropped at a
  predetermined location
• Modification requires hardwiring
• Electro-optical devices

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Agile Networks

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

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Wavelength Routing

• Wavelength dependent routing
• All optical is desirable for less complexity

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MEMs Technology

• Micro Electro-Mechanical Mirrors
• Mirror manufactured on silicon
• Mechanically controlled

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A mirror
MEMS Technology for Optical Networking
Applications A. Neukermans, R. Ramswami, IEEE
Comm. Mag., Jan 2001

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

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MEMS Cross-connect
MEMS Technology for Optical Networking
Applications A. Neukermans, R. Ramswami, IEEE
Comm. Mag., Jan 2001

• An Optical Cross-connect (1152 x 1152)

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MEMs X-Connect for Add/Drop

• O/E/O conversion not needed

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