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 characterization: Experimental setup PC for Remote Control & Data Storage Tunable Laser Source (TLS) (1510 –1625 nm)  = 0.1 nm Polarization Analyzer (PA) (Jones Matrix Eigen Analysis) Instrument Controller Fiber loopback: 95-km span of slotted-core, direct buried fiber-optic cable made available by Sprint. 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. 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 3.7 _ Span 1 MTBO6.39 years1648 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 75 km 10 Gb/s per channel 25channels 75 km DCF/EDFA... DCF/EDFA Rx Tx

11. FiberSim: Eye Diagrams vs. Distance @ 75km @ 450km@ 750km@ 1050km SSMF Link 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 Project goals: Increase optical system capacity Improve dispersion tolerance Improve PMD tolerance Improve optical bandwidth efficiency Improve data rate granularity PI: Ron Hui Sponsor: Sprint

14. Efficient optical modulation formats : WDM + SCM

15. 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 Normalized Optical spectral density (dB) Frequency (GHz) -50-40-30-20-10010203040 -35 -30 -25 -20 -15 -10 -5 0 Efficient optical modulation formats : Optical single side-band (SSB) modulation

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

17. f1f1  D n+1 D n+2 D 2n  D1D1 D2D2 DnDn f2f2 fnfn 90 o Hybrid Laser EDFA AC Bias DC Optical output Efficient optical modulation formats: OFDM transmitter use both sidebands with carrier suppression: Two sidebands but each carrying different data channels

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

19. III-nitride wide bandgap semiconductors for optical communications III-nitride wide bandgap semiconductors for optical communications 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 PI: Ron Hui Sponsor: NSF

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

21. 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 III-nitride wide bandgap semiconductors: What we have achieved 13.6713.6913.7113.7313.75 Output power (linear scale) Probe displacement (mm) An example of 3-dB coupler

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

23. Low coherent, high-resolution WDM reflectometry for fiber-length measurement 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 PI: Ron HuiSponsor: NSF-EPSCoR Monitor Crustal motion using space- born interferometer is sensitive to environmental change and weather condition

24. LED 1 LED 2 LED m WDM Multiplexer Test arm 1 3 2 lflf lflf Tunable delay line m Reference arm PZ T cos(  t) Tunable optical filter Optical receiver Signal output Phase reference FBG array 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 56789101112 Length (mm) Low coherent, high-resolution WDM reflectometry for fiber-length measurement

25. Measurement with 1-km fiber and over 3 days Low coherent, high-resolution WDM reflectometry for Fiber-length measurement

26. Lightwave: Technology transfer in 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 transfer in 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.