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