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Lightwave Communication Systems Research

Lightwave Communication Systems Research. Chris Allen Ken Demarest Ron Hui. Overview of lightwave research. PMD characterization of installed fibers Development of FiberSim (a full-fidelity fiber link simulator) Efficient optical modulation formats

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Lightwave Communication Systems Research

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  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. PC for Remote Control & Data Storage Instrument Controller Fiber loopback: 95-km span of slotted-core, direct buried fiber-optic cable made available by Sprint. Tunable Laser Source (TLS) (1510 –1625 nm) Dl = 0.1 nm Polarization Analyzer (PA) (Jones Matrix Eigen Analysis) PMD characterization:Experimental 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.

  5. PMD characterization:DGD 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.

  6. PMD characterization:Probability density function • Observations • Measured data show good agreement with Maxwellian distribution. • There is a low probability of high DGD events (i.e., DGD > 3 mean DGD).

  7. PMD characterization:Results and conclusions • Theoretical results from outage model: • Rx Threshold 3 <DGD> 3.7 <DGD>_ • Span 1 • MTBO 6.39 years 1648 years • Outage duration 136 minutes 108 minutes • MTBOs: mean time between outages

  8. 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

  9. KU’s FiberSim

  10. FiberSim:SMF/Leaf Comparison 25 channels 75 km 75 km 10 Gb/s Tx per channel DCF/EDFA DCF/EDFA 75 km . . . Rx DCF/EDFA

  11. FiberSim:Eye Diagrams vs. Distance SSMF Link @ 75km @ 450km @ 750km @ 1050km NZDSF Link

  12. 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.

  13. 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

  14. Transmitter 1 Receiver 1 f f 1 l 1 ch.1 1 ch.1 LD f f 2 2 ch.2 ch.2 S . S . f . f n . n Add/drop l ch.n 1 ch.n Optical MUX Receiver m Optical DMUX Transmitter m f f 1 1 ch.1 ch.1 l m f f 2 2 ch.2 ch.2 S S . . f f . . n n LD ch.n ch.n l m Efficient optical modulation formats: WDM + SCM

  15. 0 -5 -10 -15 Normalized Optical spectral density (dB) -20 -25 -30 -35 -50 -40 -30 -20 -10 0 10 20 30 40 Frequency (GHz) Efficient optical modulation formats:Optical 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

  16. RF detection S Polarization controller RF detection (a) Tx PBS Spliter Control algorithm Amp. LPF To decision circuit (b) PD 2 PD 2 PD 1 PD 1 Efficient optical modulation formats:Combat PMD-induced signal fadingusing diversity SCM receiver

  17. Optical output S AC f1 f2 fn 90o Hybrid DC S AC Bias Laser EDFA Dn+1 Dn+2 D2n D1 D2 Dn Efficient optical modulation formats:OFDM transmitter use both sidebands with carrier suppression: Two sidebands but each carrying different data channels

  18. Duo-binary eye diagram Binary PRBS Binary PRBS Binary PRBS Low-pass 1/4 datarate Low-pass 1/4 datarate Low-pass 1/4 datarate Duo-binary Binary EDFA S OSSB modulator Binary optical receiver Laser Efficient optical modulation formats:Optical duo-binary in a multi-tributary FDM system

  19. 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

  20. Carrier-effect phase shifters Optical waveguide l-selected signal out Multi-l signal in electrodes Switch control III-nitride wide bandgap semiconductors:Array waveguide optical switch concept

  21. Output power (linear scale) Probe displacement (mm) 13.67 13.69 13.71 13.73 13.75 III-nitride wide bandgap semiconductors:What 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

  22. Example of simulated waveguide switch in a MZ configuration port 1 signal Measurement of birefringence effect signal TE mode Wavelength (nm) TM + TM TM mode port 2 Wavelength (nm) 1 2 3

  23. 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

  24. Test arm LED l1 LED l2 WDM Multiplexer Reference arm Tunable delay line FBG array PZT lf lf LED lm l1 l2 l3 lm Phase reference cos(Wt) Signal output Tunable optical filter 5 6 7 8 9 10 11 12 Length (mm) Optical receiver 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.

  27. 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.

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