Photodetector imbalaces equalization in an optical DPSK modulation

Modern high-capacity communication systems that use differential phase-shift keying (DPSK) over optical fiber compromise their performance due to front-end stage imperfections at the receiver. In this work we present a compensation strategy to mitigate the distorsion produced by the responsivity mismatch and the temporal imbalance in the balanced photo-detector, for a optics communication system with DPSK modulation. We develop the mathematical model for the signals, taking into account imperfections and the system noise. Based on this model we deduce the equalizer as a Wiener filter and study the performance under different situations by means of numeric simulations. We also compare the bit error probabilities of the ideal, the uncompensated and the equalized DPSK receivers. Finally, we analyze the optimal number of filter coefficients taking into account the relation between performance and computational load.