Polarization Diversity Receiver for PMD Mitigation

Abstract

Polarization mode dispersion (PMD) is a signifi-cant barrier to achieving single-channel data rates at 10 Gbit/s and beyond in optical communication systems. PMD results in pulse broadening and distortion, and leads to system performance degradation. A considerable effort has been devoted in recent years to mitigate the effects of PMD, based on optical, electrical, and opto-electrical PMD compensators. Among the PMD compensation techniques, electrical domain (post-detection) approaches are particularly attractive because of their potential for compact and cost-effective implementation in the chip sets at the receiver. Electronic equalizers using simple feedforward and decision feedback structures have been proposed for mitigating intersymbol interference (ISI) in optical communications, and have been recently implemented and tested at 10 Gbit/s using integrated SiGe technology as analog equalizers for PMD mitigation. However, it is noted that they do not deliver the performance gains typically expected and the optimization of filter coefficients adaptively, even with the simple least mean squares (LMS) algorithm, is still a challenging task at the high data rates at which optical systems operate. Since all high-data-rate systems use direct detection, the polarization phase information is lost during detection and polarization diversity can provide additional advantages for PMD mitigation by making more efficient use of the available information.