TABLE OF CONTENTS In the early 1990s, the deleterious effects of PMD were first reported in transmission of analog signals over Hybrid Fiber Coax (HFC) networks [34, 35]. The transmission distances in these networks were not long (typically <50 km), but the analog signals (unlike digital ones) were very sensitive to small levels of impairment that can be generated by unwanted dispersion. Here, it was found that chromatic dispersion, which is deterministic and can be compensated, was not the only impairment, but that PMD, coupled with source laser frequency chirp, was also playing a critical role. Since that time, fiber PMD has been improved far beyond the limits where this analog limitation is observed (for systems with small source frequency chirp). However, digital signal transmission rates increased, and PMD was found to be a limiting factor in long-haul transmission. Modern state-of-the art optical fiber for transmission is capable of carrying signal line rates of 10 40 Gbps over distances of thousands of kilometers without serious degradation due to PMD. Dispersion compensating fibers and some other specialty fibers pose a PMD concern because of the difficulty in manufacturing a small fiber core with an optically uniform circular cross-section. In this case, careful manufacturing controls and measurement are required to produce a reliable product. A fair amount of work has been devoted to PMD compensation. This generally is possible when the PMD is due to a fixed component (such as a LiNb modulator). For the fiber generated PMD, the compensation...
