Transcript Lightwave Communications Systems Research University of Kansas

Lightwave Communications
Systems Research at the
University of Kansas
Objectives and Benefits to Sprint
•
•
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
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
Major Results and
Technology Transfer
•
•
•
•
•
•
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
Current Activities
•
•
•
•
WDM Modeling/measurements
Subcarrier modulation
PMD compensation
Link quality monitoring
The KU Soliton Source
All-Optical Clock Recovery
•
Goal:
•
What we accomplished
To make optical networks optically transparent by performing
clock recovery without electronics
• Developed an all-optical clock recovery device compatible
with WDM
• Patent application
All-Optical Clock
Recovery Using SBS
Data signal in
Downshifts
frequency (ƒseed)
Clock signal out
80
20
10.9 GHz
Isolator
Mod
ƒ
ƒdata
ƒstokes
Fiber
ƒdata
Interaction of data and
index grating produce
cw propagating stokes
ƒ
ƒphonon
ƒstokes
Index grating
produced by data
filters the clock
from the seed.
ƒdata
ƒclock
ƒseed
ƒdata
Stokes wave generated
by interaction of data
and index grating
provides amplification
ƒdata
ƒ
ƒ
ƒ
WDM Clock Recovery
Input
Output
=1.557 m
10 Gbps
27-1 prbs
=1.556 m
1
Clock signal out
Data signal in
1
2
2
10.9GHz
Mod
Pump
20 km DSF
fiber
100 ps/div
Seed
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
120 km
System 1
System 2
Tx
Tx
120 km
120 km
120 km
SMF
SMF
SMF
SMF
120 km
120 km
120 km
120 km
DSF
DSF
SMF
SMF
120 km
SMF
120 km
SMF
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
Rx
Rx
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
Bandwidth Expanding Factors in DSF and SMF
Spectral expanding factor for
100 km DSF and 100 km SMF
Bandwidth Expanding
Factor
1.45
1.4
DSF
1.35
1.3
1.25
1.2
1.15
SMF
1.1
1.05
1
0
10
20
30
40
50
60
70
80
90
100
Distance (km)
30
25
20
15
10
5
0
System 1
Bit Rate: 2.5 Gb/s
Channel Number: 4
Number of Samples/bit: 64
Channel Wavelength: 1553.50 nm
Pulse intensity (mW)
Pulse intensity (mW)
Calculated eye-diagrams
30
25
20
System 2
Bit Rate: 2.5 Gb/s
Channel Number: 4
Number of Samples/bit: 64
Channel Wavelength: 1553.50 nm
15
10
5
0
100
200
300
400
500
600
700
800
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
0
Intensity (dB)
optical carrier
ch1
-5
Advantage of optical SSB:
ch2
1. Better bandwidth utilization
-10
2. Possibility of moving dispersion
compensation to electronics
domain
-15
-20
-20
-10
0
10
Frequency Offset (GHz)
20
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