Polarization mode dispersion (PMD) is considered to be the main limitation for high-speed transmission system (40 Gb/s per channel) in terms of maximum single channel bit rate and transmission length (>500 km).1 Several different electrical and optical methods for mitigation of PMD induced InterSymbol Interference (ISI) have been demonstrated.2 The majority of optical PMDCs are built by incorporating a series of concatenated stages, where each stage contains a po-larization controller (PC) followed by a bire-frigent element (BE). The simplest architecture in terms of complexity, consists of only one stage, while more complex versions were demonstrated with 73 cells,3 resulting in better equalization performance, but requiring a more complex control algorithm. A one stage PMDC can compensate completely for an arbitrary amount of 1st order PMD, and thus higher order PMD becomes the significant limitation for equalization, as explained in the theoretical section to follow. It is known that RZ signals can suffer a lot of degradation from higher order PMD. Here we show that an optical bandwidth reduction on the receiver side can mitigate signal distortion from higher order PMD. Due to nonlinear propagation effects, lower bandwidth data formats, like NRZ, are not suitable for on-off keying in longhaul transmission, making the use of RZ signals necessary. However a narrow bandwidth optical filter on the receiver can provide both advantages: RZ pulse transmission and less PMD sensitive narrow bandwidth signals in front of the detector.
© 2002 Optical Society of AmericaPDF Article
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