Study on the PMD impairment of optical multilevel DPSK systems and its mitigation methods

We examine the polarization-mode dispersion (PMD) impairment of optical multilevel differential phase-shift keying systems, and also its mitigation method by comparing the electrical equalization technique and the receiver bandwidth optimization. Analysis has been carried out with 40-Gb/s systems experiencing 0/spl sim/60 ps of instantaneous differential group delay, corresponding up to 240%/80% of bit/symbol transmission rate. Results show considerable improvement in the PMD tolerance for return-to-zero format for the optimized receiver bandwidth either with or without the electrical equalization. For nonreturn-to-zero, the bandwidth optimization alone does not significantly improve the system's PMD tolerances.