Alan E' Willner

1
SC141
Combating Degrading Effects in Non-Static and
Reconfigurable WDM Systems and Networks
Alan E. Willner
University of Southern California
February 23, 2004
2
Outline
1. Introduction to Reconfigurable
Networks 2. Degrading Effects in
Systems 3. Optical Amplifiers 4. Dispersion
Compensation 5. Polarization Mode
Dispersion 6. Modulation Formats 7. Performance
Monitoring 8. Optical Switching
3
Skiing Optical Fiber Trails
Beginner
Intermediate
Advanced
Bunny
Extreme
OC-48 2.5 Gb/s
OC-192 10 Gb/s
OC-768 40 Gb/s
OC-3072 160 Gb/s
OC-12 622 Mb/s
Alan Willner James Harris (Stanford)
4
Introduction Outline

• Background
• Motivation
• What is a Non-Static or Reconfigurable Network?
• What are the Component Technologies?
• Issues
• Drivers
• Basic Phenomena
• Degrading Effects
• Compensation Techniques

5
Quote from Bob Lucky at ATT Bell Labs in 89
Just like the super-highway builders of the
1950s and 1960s, you are putting yourselves out
of business by building so much infrastructure.
Growth of automobile traffic is a few /year, but
growth of internet traffic is ?100 /year.
The Capacity vs. Demand Cycle
Demand
Growth
The capacity-vs.-demand cycle will change much
more rapidly for communications than for roads.
Capacity
Time
6
Estimated Network Load

ACTUAL


P.E. White, Bellcore, Jan. 1993 (Courtesy of
T. Li, ATT)
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The Bandwidth of Tomorrows Immersive Reality
The bandwidth of human visual audio perception
Vision
120 samples/degree 60 frames/second 16
bits/sample color, 3D
????? ?
Sound
????? ?
7,200 channels (one every 3 )
30 Gb/s
10.4 Gb/s
Vision
Sound
Reality 40.4 Gb/s
Tom Holman, USC, Multimedia Center, 2001
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You can transmit 8 bandwidth over 0 distance !!
L. Mollenauer, 1990
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Continued Capacity Growth
OC-192 (10 Gb/s)
Fundamental limits
Data rate
Capacity increase
OC-48 (2.5 Gb/s)
1
10
100
1000
Wavelengths per fiber
10
Limitations of Optics
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Sustained Growth in Capacity
Capacity Toward 25 Tbit/s
Higher Spectral Efficiency
Wider Optical Bandwidth
Closer Channel Spacing
Higher Data Rate
0.05 Bits/Hz gt1 Bits/Hz
OC-48 OC-768
100 GHz 12.5 GHz
10 nm 300 nm

• Chromatic Dispersion

• Novel Modulation Format

• L-band EDFAs

• Fiber Nonlinearity

• Raman Amplifiers

• Channel Xtalk

• Polarization or bidirectional interleaving

• Fiber Nonlinearity

• Available Components

• Polarization Mode Dispersion

12
Optimized Systems
Dispersion effects
High power
Gain fluctuation
Spectral efficiency
Nonlinearity
COST!!
Wide bandwidth
All the trade-offs should be well balanced to
optimize a system
13
Generic Requirements of Optical Networking

• Protocol transparent
• Scalability
• Reliability
• Ease of installation and management
• Network flexibility
• Reduced cost

14
Motivation
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Non-static and Reconfigurable Optical Systems
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Advantages of Reconfigurability
The ability to reconfigure light paths allows

dynamic network optimization to accommodate

changing traffic patterns
A reconfigurable

Static Topology
0.1
WDM topology

supports 6 times the

Blocking Probability
Configurable Topology
0.01
traffic of a fixed

WDM topology for

WDM ring, 20 nodes
the same blocking

One transceiver per node
0.001
probability
Call bandwidth 1 wavelength
0.01
0.02
0.03
0.04
0.05
Call Arrival Rate
V.W.S. Chan et al, JLT, 1998
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Impairment- Security-Aware Routing

• Present network very few variables (i.e. of
  hops) are used to determine the routing table
  although there are several variables on the
  physical state
• Future networks
• Monitor the channel quality and link security and
  update the routing look-up tables continually
• In the routing decisions ensure that
• Channels achieve acceptable BER
• Network achieves sufficient transmission and
  protection capacity
• Highest priority data is transmitted on the
  strongest and most secure links

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Window of Operability

• Window of operability is shrinking as systems
  become more complex
• Ensuring a long-term stable and healthy network
  is tricky

bit rate
format
number of channels
power
nonlinearities
polarization effects
dispersion
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Bandwidth Granularity

• WDM granularity does not fit the needs of end
  users
• - A wavelength is too much
• Must efficiently parcel bandwidth at the network
  edge
• - Different multiplexing? (OCDMA,
  Subcarriers )

???
???
Wavelength
WDM
OCDMA
SCM
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Path Dependency
l
2
4
i
l
k
1
SNR
i
??
3
6
SNR
k
5

• Parameters
• Dispersion
• Gain
• Noise
• Power
• Chirp

• Dependent on
• Network topology
• Routing
• Wavelength assignments
• Traffic Pattern

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Basic WDM Add/Drop
High Capacity Traffic
Through Traffic
?1
?2
?1, ?2, ?n
?1, ?2, ?n
1xN ?-DEMUX
Nx1 ?-MUX


?n
Traditional Single-Channel Add/Drop
Electric Add/Drop MUX/DMUX
High-Speed Traffic
High Speed Electronic Add/Drop

• Custom Provisioning
• Right-Speed Electronics
• Enhanced Reliability
• Lower Cost

...
...
...
...
Local Traffic
Low-Speed Electronic Add/Drop
...
...
Tingye Li, ATT Labs-Research
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Reconfigurable

Space
...
l

l
1
4
WDM
WDM
Switch
Mux
Demux
l
for
1
Space
...
l

l
1
4
WDM
WDM
Switch
Mux
Demux
l
for
2
INPUTS
OUTPUTS
Space
...
l

l
1
4
WDM
WDM
Switch
Mux
Demux
l
for
3
Space
...
l

l
1
4
WDM
WDM
Switch
Mux
Demux
l
for
4
Electronic Control
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Self-Healing Dual-Fiber Ring
Fiber Break
Switching Node

• For present circuit-switched networks,
  restoration should be lt 50ms

• Fiber break must be detected using supervision.

• Redirection of signal is achieved by using
  simple 2 x 2 optical switches.

Restoration Switch
Dual Fiber Ring
2 x 2 Optical Crossbar Switch
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Islands of Transparency

• Gateways between small networks can
  beall-optical (transparent) or optoelectronic
  (opaque).

• Opaque networks enable more

? interoperability
? reliability
? flexibility
Adel Saleh, Corvis, and Evan Goldstein, ATT Labs
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Sensitivities
Many optical network components are inherently
sensitive to changes in polarization, wavelength,
and temperature.

• Polarization - modulators, AWGs, and other
  devices with non-circular waveguides or other
  anisotropy
• induces polarization dependent loss (PDL)
• Wavelength - filters, detectors, AWGs, EDFAs,
  etc.
• Temperature - lasers, fiber Bragg gratings,
  etalons, etc.
• induces wavelength drift

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Contention Resolution
Contention resolution is required when multiple
input ports request a communications path with
the same output port

• Solutions include
• Wavelength conversion (WDM)
• Time-slot interchange (TDM)
• Deflection routing
• Optical buffering

l
Network
1
Node
l
1
l
2
Wavelength Converter
l
1
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Required Optical Components
Complex microwave design challenges

• Everything gets harder at 40 Gbit/s.

Driver
Tunable Compensation
Laser
Modulator
Receiver
Raman
LiNbO3
Preamp
Chromatic dispersion
Electro- absorption
Low Noise EDFA
PMD

• Components are extremely difficult to produce in
  quantity.
• PMD compensators might be viewed as the last
  unknown key enabler for 40-Gbit/s systems.

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Bit-Rate Distance Product
?
? WHATS NEXT ?? ? WDM Optical Amplifiers ?
Optical Amplifiers ? Coherent Detection ? 1.5?m
Single-Frequency Laser ? 1.3?m SM Fiber ? 0.8?m
MM Fiber
Bit Rate -Distance ( Gb/s ? km)
?
?
?
?
?
?
?
1970 1975 1980 1985 1990
1995 2000 2005
Year
Source Tingye Li and Herwig Kogelnik