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. ‘96
• 600 ft2 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 GHz80 20
Data signal in Clock signal out
Fiber
ModIsolator
ƒƒdataƒstokes
ƒƒdata
ƒƒdataƒclock
ƒ
ƒdataƒstokes
ƒphonon
ƒdataƒseed
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 (ƒseed)
Interaction of data and index grating produce cw propagating stokes
All-Optical ClockRecovery Using SBS
WDM Clock Recovery
=1.557 m
100 ps/div
=1.556 m
10 Gbps27-1 prbs
Output Input
Data signal in Clock signal out
Mod
10.9GHz
Pump Seed
fiber
20 km DSF
1
2
1
2
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
Tx RxSMF SMF SMF SMF SMF
120 km 120 km 120 km 120 km 120 km
Tx RxDSF DSF SMF SMF SMF
120 km 120 km 120 km 120 km 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
0
5
10
15
20
25
30
Puls
e in
tens
ity (m
W)
Bit Rate: 2.5 Gb/sChannel Number: 4Number of Samples/bit: 64 Channel Wavelength: 1553.50 nm
100 200 300 400 500 600 700 8000
5
10
15
20
25
30
Puls
e in
tens
ity (m
W) Bit Rate: 2.5 Gb/s
Channel Number: 4Number of Samples/bit: 64 Channel Wavelength: 1553.50 nm
0 10 20 30 40 50 60 70 80 90 1001
1.05
1.1
1.15
1.2
1.25
1.3
1.35
1.4
1.45
Distance (km)
Ban
dwid
th E
xpan
ding
F
acto
r
Bandwidth Expanding Factors in DSF and SMF
Spectral expanding factor for100 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 Optical single-sideband techniquetechnique
-20
-15
-10
-5
0
-20 -10 0 10 20
Frequency Offset (GHz)
Inte
nsity
(dB)
ch2ch1
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