Improvement of BER performance by active PMD compensation employing the steepest descent-based tracking algorithm

Abstract

We report improvements of signal quality by steepestdescent based tracking compensation of fast PMD fluctuations. Transmission simulations at 160 Gb/s show that bit-error-ratio characteristics are improved by 1.7 dB. IntroductionAdaptive polarization mode dispersion (PMD) compensation is required for high-speed optical fiber transmission over 100 Gb/s. The active compensation is achieved by a tunable PMD compensator which is feedback-controlled through the PMD monitoring [1]. The typical feedback control is based on the hillclimbing method. However, it is difficult for the hillclimbing-based optimization to achieve effective compensation since the state of polarization (SOP) of the transmission fiber occasionally changes faster than the optimization speed of the compensator. It is reported that the SOP can change faster than 10 ms [2].We have therefore proposed adaptive tracking compensation algorithm based on the steepest descent method (SDM) for effective compensation of fast PMD fluctuation, and demonstrated in 160 Gb/s transmission simulations [3]. In our proposal, the partial derivatives required for the SDM approach are calculated approximately by Mueller matrices with the monitoring of SOP before a tunable PMD compensator. The stable degree of polarization (DOP) was achieved under the conditions that the SOP of the fiber changes at the rate of 0.13 rad per 4 ms in average.In this paper, we report the detailed performances of the proposed method when the interval of the SOP variation changes from 1 to 5 ms. We measured biterror-ratio (BER) characteristics by transmission simulations at 160 Gb/s. The optical signal-to-noise ratio (OSNR) required for bit-error-ratio (BER) = 10 -3 is improved by about 1.7 dB compared to the conventional hill-climbing-based optimization.