1. 40Gb/s & 100Gb/s Transport in the WAN October 10, 2007
Daniel Bihon
Fujitsu Laboratories of America, Inc.
Richardson, Texas

2. Introduction Today’s networks deploy 2.5Gbps and 10Gbps line rates
Networks will migrate to 40Gbps (and in the future to 100Gbps) per wavelength
High demand for transmission capacity
Higher rate client interfaces
Transmission Quality and Connectivity
Challenges associated with 40Gbps and 100Gbps solution:
OSNR requirement increases by 6dB and 10dB respectively
Chromatic dispersion tolerance decreases respectively (1/16-th and 1/100 of 10G system)
Similarly PMD tolerance decreases (1/4- and 1/10th of 10G system)
Significant increase to OADM filtering
Counter-measures
Advanced multi-level modulation formats
Low symbol rate
Tunable/Adaptive CD compensation
Forward error correction (FEC)
Coherent detection
PMD and CD tolerance can be further improved

3. Light Properties to Modulate
Modulate one or more light properties
Intensity modulation (on-off keying):
Widely used modulation technique for up to 10Gbps transmission
Easy to modulate and easy to detect
Phase modulation:
Well known technique but was not used in optical communications
Detection is more difficult compared to on-off keying
Polarization modulation:
Relatively new technique
Detection is difficult
Intensity
Phase (Frequency)
Polarization

4. 40 Gbps Modulation Formats
NRZ
Duobinary
CS-RZ
RZ-DPSK
RZ-DQPSK
: Advantage
Tx out
MZI out
Tx out
MZI out
: Disadvantage
“1” DPhase= 
“0” DPhase= 0
4 values are mapped to Dphase 0, /2, , 3/2
Optical spectra
Frequency (GHz)
Frequency (GHz)
Frequency (GHz)
Frequency (GHz)
Frequency (GHz)
Optical noise tolerance
poor
very poor
medium
very good
good
Chromatic dispersion tolerance
medium
good
(in linear regime)
medium
medium
good
PMD tolerance
poor
medium
medium
medium
good
Optical nonlinearity tolerance
medium
poor
good
good
good
OADM filtering tolerance
medium
good
medium
medium
good
RZ-DQPSK is attractive in many aspects for high bit-rate transmission

5. Question: How to transport 100GE in DWDM networks?
100+ Gbps Transmission
Question: How to transport 100GE in DWDM networks?
Parallel
Serial
Transport on multiple wavelengths
Requires synchronization of wavelengths due to differential propagation delay
Manage a band of wavelengths
Simpler Tx/Rx, but low fiber utilization
Transport on single wavelength
Complex Tx/Rx
Higher spectral efficiency
Higher total transport capacity over a WDM system
Transmission impairments

6. SP- and DP-QPSK for 40 and 100G
Fujitsu Laboratories is doing intensive research on SP- and DP-QPSK