Abstract

As bit-rates increase in lightwave systems, the systems become increasingly sensitive to polarization-mode dispersion (PMD) impairment. This system impairment has been studied both theoretically and experimentally for different modulation formats.^1–5 It is thought from many studies that return-to-zero (RZ) signals are more tolerant to PMD than non-return-to-zero (NRZ) signals when an optically preamplified receiver^2–5 is employed. The common explanation is that RZ pulses are confined to the middle of the bit-slot and thus have a greater timing margin than NRZ bits against PMD-induced leakage of pulses into adjacent bit slots. This tolerance of RZ formatted signals to PMD occurs in a milieu of RZ formatted signals having a baseline sensitivity that is about 2 dB better than that of NRZ formatted signals even when both signal formats are detected with a receiver with an electrical bandwidth optimized for NRZ.^2,6

© 2002 Optical Society of America