On the impact of carrier phase estimation on phase correlations in coherent fiber transmission

Carrier phase estimation (CPE) is an integral part of the digital signal processing (DSP) of coherent optical communication systems as it compensates laser phase noise (LPN) introduced by free-running transmitter and local oscillating (LO) lasers. Nonlinear interactions during propagation are another source of correlated phase noise. In this paper, we show through simulations and in experiments that blind decision-directed (DD) CPE with regular block lengths removes a large portion of the memory. This makes it virtually impossible in practice to quantify correlations that come from propagation effects, or to obtain rate gains by exploiting the nonlinear phase noise (NLPN). Larger CPE block lengths leave the memory partly intact. This, however, comes at the expense of reduced information rates. We are able to fully recover this rate loss in simulations by using idealized processing of phase distortions. In experiments with full DSP, an almost full rate recovery is reported.