Lightwave Communication Systems Research

1
Lightwave Communication Systems Research

• Chris Allen
• Ken Demarest
• Ron Hui

2
Overview of lightwave research

• PMD characterization of installed fibers
• Development of FiberSim (a full-fidelity fiber
  link simulator)
• Efficient optical modulation formats
• III-nitride wide bandgap semiconductors for
  optical communications
• Low coherent, high-resolution WDM reflectometry
  for fiber-length measurement

3
PMD characterization on installed fiber

• PI Chris Allen
  Sponsor Sprint
• Goal
• To gain an understanding of the temporal and
  spectral characteristics of PMD on an installed
  fiber link.
• Approach
• Make long-term measurements of the differential
  group delay (DGD or ??) over a range of
  wavelengths and assess its rates of change with
  time and ?.
• Desired outcome
• Provide network operators with knowledge to
  evaluate techniques for mitigating PMD-induced
  outages when channel data rates are increased.

4
PMD characterizationExperimental setup

• Over 86 days (from November 9, 2001 thru February
  2, 2002) 692 measurements were made on the 1150
  discrete wavelengths.
• Measurements were repeated about every 3 hours.

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PMD characterizationDGD vs. l and time

• 86 days of data
• 795,800 data pts
• Observations
• DGD depends on both time and ?.
• DGD varies slowly with time.
• DGD varies rapidly with ?.
• Instances of high DGD are spectrally localized.

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PMD characterizationProbability density
function

• Observations
• Measured data show good agreement with Maxwellian
  distribution.
• There is a low probability of high DGD events
  (i.e., DGD gt 3? mean DGD).

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PMD characterizationResults and conclusions

• Theoretical results from outage model
• Rx Threshold 3 ltDGDgt
  3.7 ltDGDgt_
• Span 1
• MTBO 6.39 years 1648 years
• Outage duration 136 minutes
  108 minutes
• MTBOs mean time between outages

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FiberSim development

• PI Ken Demarest Sponsor Sprint
• A full-fidelity fiber link simulator
• Dispersion, self- and x-phase modulation
• PMD, Raman gain, modulation instability
• Faster and more memory efficient than any
  commercially-available code
• Runs on Unix, Windows NT
• Utilizes parallel processors

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KUs FiberSim
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FiberSimSMF/Leaf Comparison
25
channels
75 km
75 km
10 Gb/s
Tx
per
channel
DCF/EDFA
DCF/EDFA
75 km
. . .
Rx
DCF/EDFA
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FiberSimEye Diagrams vs. Distance
SSMF Link
_at_ 75km
_at_ 450km
_at_ 750km
_at_ 1050km
NZDSF Link
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FiberSim SMF/Leaf Conclusions

• Local dispersion, not average dispersion,
  dictates FWM susceptibility.
• FWM is the dominant performance limitation on low
  dispersion links with tight carrier spacings.
• Standard single-mode fiber appears to be the
  ideal choice for dense WDM networks.

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Efficient optical modulation formats
PI Ron Hui
Sponsor Sprint

• Project goals
• Increase optical system capacity
• Improve dispersion tolerance
• Improve PMD tolerance
• Improve optical bandwidth efficiency
• Improve data rate granularity

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Efficient optical modulation formats WDM SCM
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Efficient optical modulation formatsOptical
single side-band (SSB) modulation
Measured optical SSB spectrum
Advantage of optical SSB 1. Better bandwidth
utilization 2. Less dispersion penalty 3.
Possibility of moving dispersion compensation to
electronics domain
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Efficient optical modulation formatsCombat
PMD-induced signal fadingusing diversity SCM
receiver
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Efficient optical modulation formatsOFDM
transmitter use both sidebands with carrier
suppression Two sidebands but each carrying
different data channels
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Efficient optical modulation formatsOptical
duo-binary in a multi-tributary FDM system
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III-nitride wide bandgap semiconductors for
optical communications
PI Ron Hui
Sponsor NSF
Motivation High-speed all-optical packet switch
is a required function of future intelligent
optical networks Current optical switch using
MEMs and thermal tuning of silicon optical
waveguides are too slow for packet
switching III-nitride is transparent in optical
communications wavelength windows III-nitride
semiconductor material is thermally and
mechanically stable with the refractive index
closely matches to the optical fiber The
refractive indices of III-nitride optical
waveguide can be fast tuned through carrier
injection Integrated optical waveguide devices
using GaN/AlGaN combination are realizable to
perform nanosecond all-optic packet switch
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III-nitride wide bandgap semiconductorsArray
waveguide optical switch concept
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III-nitride wide bandgap semiconductorsWhat we
have achieved
An example of 3-dB coupler
Characterized of optical properties of GaN
semiconductor materials in infrared wavelength
regions in terms of optical loss, refractive
index and birefringence Designed sing-mode
optical waveguide devices using GaN/AlGaN
semiconductor material. Beam propagation
simulation Nano-structure fabrication of optical
devices Metal organic chemical vapor deposition
(MOCVD) Inductively-coupled plasma (ICP) dry
etching
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1
2
3
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Low coherent, high-resolution WDM reflectometry
for fiber-length measurement
PI Ron Hui Sponsor NSF-EPSCoR
Project goals Monitor earth change constantly
using fiber-optic systems Predict earth quacks by
measuring crustal deformation High resolution
over a large dynamic range Insensitive to
environmental changes Device can also be used to
allocate fiber failures in fiber-optic equipment
Monitor Crustal motion using space-born
interferometer is sensitive to environmental
change and weather condition
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Low coherent, high-resolution WDM reflectometry
for fiber-length measurement
Use WDM to increase wavelength bandwidth to
improve measurement resolution Use multiple
FBGs to increase measurement coverage Use
polarization spreading in receiver to reduce
polarization sensitivity
25
Low coherent, high-resolution WDM reflectometry
for Fiber-length measurement
Measurement with 1-km fiber and over 3 days
26
Lightwave Technology transferin the past 12
months

• Journal papers
• Allen, C.T., P.K. Kondamuri, D.L. Richards, and
  D.C. Hague, "Measured temporal and spectral PMD
  characteristics and their implications for
  network-level mitigation approaches," Journal of
  Lightwave Technology, 21(1), pp. 79-86, 2003.
• Hui, R., J. Thomas, C. Allen, B. Fu and S. Gao,
  "Low-coherent, WDM reflectometry for accurate
  fiber length monitoring," IEEE Photonics
  Technology Letters, 15(1), pp. 96-98, 2003.
• Hui, R., C. Allen, and K. Demarest,
  "PMD-insensitive SCM optical receiver using
  polarization diversity," IEEE Photonics
  Technology Letters, 14(11), pp 1632-1634, 2002.
• Hui, R., B. Zhu, R. Huang, C.T. Allen, K.R.
  Demarest, and D. Richards, "Subcarrier
  multiplexing for high-speed optical
  transmission," Journal of Lightwave Technology,
  20(3), pp. 417-427, 2002.
• Other papers
• D. Richards, C. Allen, K. Demarest, and R. Hui,
  Legacy fiber meets long-haul network needs, WDM
  Solutions, pp. 14-17, March 2003.

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Lightwave Technology transferin the past 12
months

• Patents
• Demarest, K., C. Johnson, C. Allen, R. Hui,
  B.Zhu, "Method and apparatus for recovering an
  optical clock signal," U. S. Patent Number
  6,542,274 issued April 1, 2003.
• Pua, H.Y., C. Allen, K. Demarest, R. Hui, K.V.
  Peddanarappagari, "Method and apparatus to
  compensate for polarization-mode dispersion," U.
  S. Patent Number 6,459,830 issued October 1,
  2002.
• Conference papers
• Demarest, K., D. Richards, C. Allen, and R. Hui,
  "Is standard single-mode fiber the fiber to
  fulfill the needs of tomorrow's long-haul
  networks?", Proceedings of the National Fiber
  Optic Engineers Conference (NFOEC), pp. 939-946,
  Sept. 15-19, 2002.
• Allen, C., P.K. Kondamuri, D.L. Richards, and
  D.C. Hague, "Analysis and comparison of measured
  DGD data on buried single-mode fibers, Symposium
  on Optical Fiber Measurements, Boulder, CO, pp.
  195-198, Sept. 24-26, 2002.
• Allen, C., P. K. Kondamuri, D. Richards, and D.
  Hague, "Measured temporal and spectral PMD
  characteristics and their implications for
  network-level mitigation approaches," Proceedings
  of the IASTED International Conference on
  Wireless and Optical Communications, Banff,
  Alberta, Canada, 2002.
• Demarest, K., R. Hui, C. Pavanasam, M. Fei, and
  D. Richards, Numerical Comparison of WDM
  Capacity in Conventional Single Mode Fiber and
  Nonzero Dispersion-Shifted Fiber, Proceedings of
  the IASTED International Conference on Wireless
  and Optical Communications, Banff, Alberta,
  Canada, 2002.
• Hui, R., High-speed optical transmission using
  sub-carrier multiplexing, Proceedings of the
  IASTED International Conference on Wireless and
  Optical Communications, Banff, Alberta, Canada,
  2002.