System of algorithms for digital signal processing for coherent optical communications

One of the main parts of modern coherent fiber-optic transceivers is the digital signal processing unit (DSP). Its task is to compensate for the distortions of the transmitted signal occurring at the transmitter, in the fiber-optic communication line (FOCL) and at the receiver. This paper presents an analysis of existing linear DSP algorithms that allow to recover the DP-QPSK (dual polarization quadrature phase shift–keying) signal. The original implementation of the complete digital signal processing path of the receiving part is also demonstrated, tested on experimental signal data, which passed the line up to 4000 km. Demodulation results are compared with the theoretical limit and the best available commercial device.