Plenary: ACC Workshop

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Plenary ACC Workshop
Robust and Reconfigurable High-Capacity Optical
Communication Systems
Alan E. Willner
University of Southern California Los Angeles, CA
90089-2565
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Thank You !
to Drs. Ady, Arie, and Mark.
The generous support and collaboration of CISCO,
DARPA, HP, Intel, NSF, Packard Foundation and
SPAWAR.
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The OCLAB Family
OIDA Chicago vs Hawaii
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Replace Function, Not Device
Function
Electronic Device Photonic Device
Replace
Integrated Photonics
Nick Tabellion, CTO, Fujitsu Softek "The
commonly used number is For every 1 to purchase
storage, you spend 9 to have someone manage it."
Cost Equipment lt Operation lt Management
Integrated Photonics
Integrated Photonics
Enable monitoring and automated management
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Brittle Network
Bran Ferren Chief Creative Officer Applied
Minds, Inc., USA OFC - Plenary Speaker 06
Predicted bursting of bubble in 97

• Optical systems are brittle
• Optical systems are difficult to use
• Need plug-and-play robustness

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Outline

• Monitoring for Self-Managed Networks
• Heterogeneous Systems
• Reconfigurability
• Modulation Formats
• Functional Photonics
• Optical Signal Processing
• Delay Elements Using Slow Light
• Musings

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Think wireless laptop LAN
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Self-Managed Networks
B
A
C
E

• Adaptive Resources
• Diagnose and repair
• BW allocation
• Gain/Loss
• Dispersion Compensation
• ?-Routing
• Look-up tables

D
Today Measure, Make, Tweak, Pray.
Automation Intelligence Monitoring Keep the
person out of the loop
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Manual DWDM Network Life-CyclePresent Mode of
Operation
Manual provisioning of optical design parameters
Manual provisioning of equipment topology into
EMS/NMS
Manual installation, manual power measurements
and VOA tweaking at every site for every l
Manual DWDM processes labor intensive and error
prone Result high OpEx costs
R. Ramaswami, L. Paraschis
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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 difficult

bit rate
format
power
number of channels
wavelength range
distance
Monitor
Power
Wavelength
Chirp
Extinction ratio
Chromatic dispersion
Polarization mode dispersion
Nonlinearities
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Monitoring the State of the Network
Window of operability is shrinking
Monitoring is required

• Monitor non-catastrophic data degradation
• Isolate specific impairments

• Ubiquitous deployment
• Graceful routing based on physical state of
  network?

Ubiquitous Monitoring
Locate Faults
Detect Attacks
Diagnose Assess
Repair Damage
Reroute Balance Traffic
Malicious Behavior
Telcos Human Error (1/3 of outages)
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Vestigial Sideband Optical Filtering
Optical Carrier
?f
VSB-U
VSB-L
BW
fU
Frequency
fL
f0
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Q. Yu, JLT, 2003
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Polarization Mode Dispersion (PMD)
cross section
side view
Elliptical Fiber Core
1st-order PMD DGD
The 2 polarization modes propagate at different
speeds.
Probability of Exceeding a Specific DGD ()
0.1
10
50
0.1
10
50
1
1

• PMD induces randomly changing degradations.
• Critical limitation at
• gt10 Gbit/s data rates.

Probability
Distribution
Maxwellian
Maxwellian
distribution
distribution
tail
tail
0
10
20
30
40
50
0
10
20
30
40
50
0
10
20
30
40
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Differential Group Delay (ps)
Significant higher-order effects can exist.
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RF Clock Tone Fading
Two Clocks
Carrier
CD (Freq. Delay)
t
Upper
Lower clock
Upper clock
t
Lower
In Phase
?
Power
Upper Clock
PMD (AxisDelay)
f
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OSNR Monitoring Using Polarization Nulling
Polarizer (Parallel)
Ps 0.5Pase
Arbitrarily Polarized signal Unpolarized noise
0.5Pase
Polarizer (Orthogonal)
Polarization controller
Ps Pase

• The received signal (together with noise) is
  split into two orthogonal
• polarization components.
• The polarization ratio is a measure of the OSNR
  (Ps/Pase).
• The performance could be affected by various
  polarization effects (i.e., PMD,
• nonlinear birefringence, and partially
  polarized ASE noise due to
• polarization-dependent loss).

Y. C. Chung et. al., JLT, 2006
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OSNR Monitoring for Multiple Modulation Formats

• ¼ Bit Delay-line Interferometer is used for OSNR
  monitoring
• One output port gives constructive (Pconst) while
  the other port
• provides destructive interference (Pdest).
• OSNR is proportional to the Ratio (Pconst /
  Pdest)
• This method is applicable to multiple modulation
  formats

Y. Lize, et. al., ECOC 06 OFC 07
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Concept of PMD-Based Interfermetric Filter
Fast
Slow axis
SOP
Tunable DGD Emulator
Polarization Beam Splitter
Slow
RF Spectrum Analyzer
?t
Destructive
450 relative to PBS
Fast axis
Constructive
Optical Spectrum of Destructive Port
DGD-Generated Interferometric Filter
RF Spectrum
Optical Power
RF Power
?PRF
?
f
f
Near fcarrier
1/?t
FSR
lt 170 MHz (CD-insensitive)

• The two outputs of the PBS represent the
  constructive and destructive filters
• of a standard Mach-Zehnder delay-line
  interfometer (FSR 1/?t).
• At the destructive port, the monitored RF power
  will change with the DGD-
• generated interferometric filter response.

J.-Y. Yang et. al., ECOC, 2007
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Experimental Results PMD Monitoring

• The RF power measured at 170 MHz increases by
  20 dB in the
• presence of 0 to 100 ps of DGD.
• Chromatic dispersion-insensitive measurements
  to be within 1 dB.
• The performance and monitoring sensitivity is
  very similar since
• both signals have the same spectral
  bandwidth.

J.-Y. Yang et. al., ECOC, 2007
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Combined Effects of PMD and PDL
PSP1
Fiber with high PMD
PSP1 ? PSP2
Differential Group Delay PSP1 ? PSP2
PSP1
PSP2
PSP2
Polarization Mode Dispersion
??
PSP 1
PDL Frequency-dependent attenuation PMD
Enhanced time spreading
Different Attenuation PSP1 ? PSP2
Optical Components (PDL? dB)
PSP2
Polarization Dependent Loss (PDL)
B. Huttner, et al., JSTQE, 2000
L.-S. Yan, et al., PTL, 2003
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Outline

• Monitoring for Self-Managed Networks
• Heterogeneous Systems
• Reconfigurability
• Modulation Formats
• Functional Photonics
• Optical Signal Processing
• Delay Elements Using Slow Light
• Musings

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Heterogeneous Systems One Network Fits All
Different Modulation Formats
Variable QoS
Variable Bit Rate
Sub-carrier Multiplexing (DA)?
Future Heterogeneous Network
Circuit Packet Switching?
Multiple Wavelength Ranges

• Hardware should be reconfigurable and
  transparent
• An intelligent network could use the optimal
  method from
• the application/user viewpoint.

Economics Early market entry of new services
(CATV??)
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RF to Optical Transition
RF/Electronic History
Optical History
Time
Coherent Transmission Multi-level
Modulation Transatlantic Transmission FEC
Introduced by Shannon Equalization
Coherent Optical Systems Multi-level
Modulation First Transatlantic Line FEC for
Transatlantic Optical Equalization
Variable Bit Rate Systems Dynamic Bandwidth
Allocation S/W-Defined Radio
?
Coherent Systems Revisited?
Device Capabilities Drive System Applications
Variable Bit Rates Systems? Dynamic Bandwidth
Allocation? S/W-H/W Defined Reconfigurable
Optical Systems?
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Follow and Dont Follow the Leader
Dont Follow Be Creative
If somebody tells you it cant be done, dont
listen to him. - Joe Goldstein, Nobel Laureate
Remember the Inefficient 3-Level EDFA?
Follow Dont Be Foolish
Modulation Formats, OFC06
Number of Papers at OFC
( Thanks, Herwig )
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Differential Phase-Shift-Keying (DPSK)
DPSK
1
1
0
1
0
0
t
Constant optical power
RZ-DPSK
1
1
0
1
0
0
t
Pulse appears in every bit
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Concept of DPSK
Phase
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Benefit vs. Complexity Integration
Hardware complexity
Data
Mach-Zehnder modulator
Precoded Data
LP
Data
Clock
Delay interferometer
Clock
Precoded Data
Precoded Data
Clock
Control
Precoded Data

• Coherent DetectionLaser LO and 90-degree
  hybridRF post-processing and increased
  sensitivity

A. Gnauck, P. Winzer, R. Essiambre, 2005
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SlowAxis
Fast Axis
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SlowAxis
Fast Axis
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DQPSK Detection Overview
DQPSK typically requires two DLIs to detect 4
phase locations 45 in one arm of in-phase (I)
DLI -45 in one arm of quadrature (Q) DLI
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In-Phase (I)
-
T
-45
Quadrature (Q)
-
T
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Grooming Dynamic BW Allocation
- Optimize OSNR
Sensitivity Penalty Gq (dB)
Optical BW (Bit-rate)
- Efficient allocation
Pfennigbauer, et al., PTL, 2002
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Outline

• Monitoring for Self-Managed Networks
• Heterogeneous Systems
• Reconfigurability
• Modulation Formats
• Functional Photonics
• Optical Signal Processing
• Delay Elements Using Slow Light
• Musings

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Delay Applications in Optically-Routed Networks
Output ports
Packet
Switch
Buffer
Optical synchronization
Input ports
Control
Optical header recognition
Optical Switching Node
Accurate, widely-tunable optical delays are a
potentially valuable requirement for future
optically-switched networks to enable
synchronization, header recognition buffering
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Widely Tunable Optical Delay
10G NRZ
?in
?in
?in
?c
?c
Tunable ? Converter 2 PPLN
Tunable Dispersion Compensator Chirped FBG
Dispersion Module DCF
Tunable ? Converter 1 PPLN
Signal in
Signal out
Fast Lane
?in
B
B
A
A
B
Wavelength Converter 1
Dispersion Module
Wavelength Converter 2 Tunable Dispersion
Compensator
TDC
Slow Lane
?c
A
A
A

• Little additive noise
• Phase preserving (for phase modulation signal)
• Modulation format and bit rate independent

• Broadband (gt 80 nm)

Requirements for ? converter
Y. Wang, et. al., IEEE PTL, 19, 861-863 (2007)
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44-ns Tunable Delay
Relative Delay (ps)
Dispersion (ps/nm) x ? Tuning Range (nm)
Use wideband wavelength converter
Use large dispersion values
Use double pump configuration to achieve
continuous tunability over the entire range
Use dispersion compensation to restore the pulse
Double pump configuration offers much wider delay
tunability compared to single pump configuration
Y. Wang, et. al., IEEE PTL, 19, 861-863 (2007)
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Bits Delay vs. Tuning Wavelength
Tuning laser (nm)
10 Gb/s Bits (500ps/div)
1548.40
Delay (ps)
1548.90
1549.42
Tuning wavelength (nm)

• Delay is varied by tuning the laser ?
• Wide tunability is achieved by using a 2-pump
  PPLN configuration and 2000 ps/nm dispersion
  module
• Continuous tunability up to 44-ns is demonstrated
  for a 10 Gb/s NRZ system

Y. Wang, ECOC 2005 PTL 2007
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Packet Processing using Widely-Tunable Delay
l2
lc
l1
Dispersive Media
P P L N
P P L N
l1
Intra-Channel Dispersion Compensator
DCF
?T Delay
time
Intra-channel dispersion
Inter-channel dispersion
DCF dispersion X ?lconverted
Delay
I. Fazal, et. al., Optics. Express, 15, (2007)
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Packet Synchronization and Multiplexing
l2 (non-delayed)
Packet length 196 bits _at_10G
l2
MUX
l1(delayed by 26.4ns)
l1
Delay Module
l1 and l2 and multiplexed
time
Reconfigurability

• Two packet streams _at_ 10G synchronized and
  multiplexed
• Reconfiguration time of lt 300 ps demonstrated

I. Fazal, et. al., Optics. Express, 15, (2007)
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Slow Light Techniques and Applications
Slow Light

• Tunable Delay Line
• Synchronization
• Optical TDM Mux

• Optical Buffers
• Storage capacity
• Maximum delay

• Signal Processing
• Delay Resolution
• Reconfigurability

Promising techniques to achieve tunable delay for
Gbit/s data

• Stimulated Brillouin Scattering (SBS) in fiber
• Stimulated Raman Scattering (SRS) in fiber
• Optical Parametric Amplification (OPA) in fiber
• Spectral hole burning in SOAs

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Motivation (1) Tunable OTDM

• Slow-Light-based OTDM multiplexer offers
  continuous tunability which can dynamically
  adjust the offsets among input channels.
• Multi-channel slow light can also be utilized
  for future N1 (N gt 2) synchronizer and optical
  time division multiplexer.

B. Zhang, et. al., Optics Express, 15, (2007)
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Motivation (2) Variable-Bit-Rate
Slow-light-based OTDM multiplexer can dynamically
reconfigure its tunable delay according to
different input data bit-rates
B. Zhang, et. al., Optics Express, 15, (2007)
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Results Tunable OTDM

• The main reason for the 9-dB penalty reduction
  is the reduced beating region caused by
  bit-overlapping at same wavelength.

• Residual beating still exists due to
  slow-light-induced pulse broadening.

B. Zhang, et. al., Optics Express, 15, (2007)
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Outline

• Monitoring for Self-Managed Networks
• Heterogeneous Systems
• Reconfigurability
• Modulation Formats
• Functional Photonics
• Optical Signal Processing
• Delay Elements Using Slow Light
• Musings

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What about ultra-high-speed research?
Great, go for it, many potential
applications!!For telecom, be watchful. Will
10-Gbit/s become the HP 12C calculator of the
optical communications world?
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Available Jobs Are Like Icebergs
Advertised
Not advertised

• Everything was advertised during bubble.
• Normal hiring is much more ad hoc.
• Be proactive.

Jobs
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Summary

• Integrated Photonics might dramatically change
  the cost, robustness and performance of a
  communication system.
• A force-multiplier is to enable a function
  rather than simply replace a device 1-for-1.
• There are a rich set of research problems that
  must be pursued to herald this vision.

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Bit-Rate Distance Product
?
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? WHATS NEXT ?? Spectrally-Efficient
Modulation Formats ? WDM Optical Amplifiers ?
Optical Amplifiers ? Coherent Detection ?
1.5?m Single-Frequency Laser ? 1.3?m SM Fiber ?
0.8?m MM Fiber
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Bit Rate -Distance ( Gb/s ? km)
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1975 1980 1985 1990 1995 2000
2005 2010
Year
Source Tingye Li and Herwig Kogelnik