Statistical Analysis of Equalization Enhanced Phase Noise in Coherent Fiber Optical Communications

Coherent optical communications increase the receiver sensitivity and the total capacity. Together with high speed digital signal processing (DSP), compensation for linear transmission impairments (chromatic dispersion, polarization mode dispersion and phase noise) can be achieved. In the past, many algorithms have been developed for this purpose: we offer an overview of those. However, in dispersion unmanaged coherent optical links, even after DSP, the received constellation remains influenced by enhanced noise commonly known as equalization enhanced phase noise (EEPN). Its properties are explained in further details using statistical analysis. Statistical properties of EEPN are compared with that of additive white gaussian noise (AWGN) and pure phase noise (PN) by numerical simulations complemented with explanation of mean, variance and autocorrelation function. Finally, the possibility to use only digital post-processing for EEPN (similar to PN) is discussed and shown to be not feasible