Improved polarization-mode-dispersion tolerance in duobinary transmission

Polarization-mode-dispersion tolerance of a low-pass filter duobinary modulation format is investigated. With the optimum residual dispersion, the optical signal-to-noise ratio penalty at a differential group delay of 40 ps is measured to be 1 dB (at BER=6/spl times/10/sup -5/): 1.5 dB less than that without residual dispersion in a 10.7-Gb/s duobinary transmission. Numerical simulations show reasonable agreement with the experimental results.