Lightwave Communications Systems Research at the University of Kansas

Development of techniques and identification of tradeoffs for increasing Sprint’s network capacity while maintaining reliability Identifying and evaluating long-range technology trends Evaluating the feasibility of new technologies for Sprint’s network Resource of graduates educated in state of the art lightwave communication systems Objectives and Benefits to Sprint

Laboratory Infrastructure Started Jan. ‘ ft 2 laboratory space Key test equipment includes Lucent FT-2000 WDM system Ciena 16 system Soliton generator (built at KU) Recirculating loop (built at KU) Optical Clock Recovery (built at KU)

Participants Faculty: Ken Demarest (WDM Systems, modeling) Chris Allen (WDM and coherent systems) Rongqing Hui (WDM systems, devices) Victor Frost (ATM, SONET, networking) Postdoctoral Fellows: 1 Students: 6 Graduate, 3 undergraduate

1 Patent and 2 patent applications 11 Papers in major photonics journals Development of soliton generator and circulating loop testbed WDM modeling software and measurements PMD compensation and measurement techniques Subcarrier modulation Major Results and Technology Transfer

Current Activities WDM Modeling/measurements Subcarrier modulation PMD compensation Link quality monitoring

The KU Soliton Source

All-Optical Clock Recovery Goal: To make optical networks optically transparent by performing clock recovery without electronics What we accomplished Developed an all-optical clock recovery device compatible with WDM Patent application

10.9 GHz Data signal inClock signal out Fiber Mod Isolator ƒ ƒ data ƒ stokes ƒ ƒ data ƒ ƒ clock ƒ ƒ data ƒ stokes ƒ phonon ƒ data ƒ seed Index grating produced by data filters the clock from the seed. Stokes wave generated by interaction of data and index grating provides amplification ƒ Downshifts frequency (ƒ seed ) Interaction of data and index grating produce cw propagating stokes All-Optical Clock Recovery Using SBS

WDM Clock Recovery =1.557  m 100 ps/div =1.556  m 10 Gbps prbs Output Input

Modeling and Measurements Goal: Model fiber link and network performance for dense wavelength division multiplexed operation What we’ve done Developed high fidelity model for fiber transport Applied model to address WDM over DSF issues raised by Sprint What we’re doing Increasing the capabilities of this model to handle hundreds of optical channels simultaneously. Modeling legacy network performance at 40 Gb/s

WDM Simulator

NEC WDM System on DSF/SMF Two OC-48, WDM system configurations TxRx SMF 120 km TxRx DSF SMF 120 km System 1 System 2 Dispersion: SMF: ~ 16 ps/km-nm, DSF: ~ 0 ps/km-nm Expectations: System 2 has better performance (less dispersion) Reality: System 1: error free, System 2: mass errors

NEC WDM System on DSF/SMF What we found: Strong cross phase modulation (XPM ) in the DSF caused spectral broadening High dispersion in the SMF caused pulse-width broadening

NEC WDM System on DSF/SMF Pulse intensity (mW) Bit Rate: 2.5 Gb/s Channel Number: 4 Number of Samples/bit: 64 Channel Wavelength: nm Pulse intensity (mW) Bit Rate: 2.5 Gb/s Channel Number: 4 Number of Samples/bit: 64 Channel Wavelength: nm Distance (km) Bandwidth Expanding Factor Bandwidth Expanding Factors in DSF and SMF Spectral expanding factor for 100 km DSF and 100 km SMF Calculated eye-diagrams System 1 System 2 DSF SMF

Subcarrier Modulation Techniques Goal: Increase fiber link capacity and flexibility by multiplexing several digital signals on a single optical carrier What we’ve done Modeled optical subcarrier modulation systems Constructed and tested a 2-channel system What we’re planning to do Construct and test a 4-channel system Determine the commercial feasibility of optical subcarrier systems for digital applications on long links.

Optical single-sideband technique ch2 ch1 optical carrier Advantage of optical SSB: 1. Better bandwidth utilization 2. Possibility of moving dispersion compensation to electronics domain

PMD Compensation Goal Increase fiber link data rates by reducing the effects of polarization mode dispersion (PMD) What we’ve done Developed a scheme for compensating first order PMD Demonstrated a prototype What we’re planning to do Measure the PMD on a Lawrence-K.C. link Test our compensation scheme on this link

PMD Compensation

Current Thrusts PMD Compensation Dense WDM modeling Subcarrier modulation