All-order polarization mode dispersion sensing and compensation in optical fiber communication systems
Polarization Mode Dispersion (PMD) is considered a major obstacle for ultrahigh-capacity fiber communication systems at 40 Gbaud/s and above. It arises from the residual birefringence of the optical fiber, and causes a differential group delay between different polarizations. If the delay is comparable to a significant fraction of the bit period, adjacent bits may overlap, leading to an increase in bit error rate. Moreover, for polarization multiplexing (Pol-Mux) used in ultrahigh-capacity fiber systems as an important method to improve spectral efficiency, PMD not only couples polarization-multiplexed channels, but also lowers transmission tolerance to fiber nonlinearity and chromatic dispersion. Therefore, for fiber spans in which the PMD is not very small, PMD compensation (PMDC) is required.^ PMD monitoring is an essential part of PMDC. Since PMD can occasionally vary on a millisecond scale, and the frequency dependence of the PMD becomes important, a fast frequency-resolved monitoring tool is preferred. We experimentally apply a unique high-speed spectral polarimeter to realize near-real-time broadband Polarization Mode Dispersion (PMD) measurements.^ Based on PMD sensing work, our group has previously performed all-order PMD compensation via hyperfine resolution optical pulse shaping for isolated short pulses. This scheme works more efficiently than the traditional compensators that are limited to the low-order PMD regime and valid only for small distortion compared with pulse width. Here for the first time, we apply this technique in optical fiber communication system experiments: (1) 40 Gbit/s systems; (2) 10 Gbit/s×2 Pol-Mux systems. For the 40 Gbit/s system, we construct a test-bed realized by 10 Gbit/s × 4 optical time division multiplexing (OTDM). With this system, employing an optical pulse shaper with 128 pixels to control 200 GHz range, we demonstrate all-order PMDC with over 50 ps mean differential group delay. For the 10 Gbit/s × 2 Pol-Mux (10% RZ) system, with the same shaper we compensate PMD with over 40 ps mean differential group delay. Both experiments can readily be extended to higher symbol rate (pulses down to sub-ps range).^
Andrew M. Weiner, Purdue University.
Engineering, Electronics and Electrical
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