I. Introduction
It has been shown that the interaction between the electronic dispersion compensation (EDC) filter and the phase noise of the local oscillator (LO) laser in the coherent receiver generates a noise called equalization enhanced phase noise (EEPN) [1]–[8]. The variance of EEPN at EDC output is computed in [1]. The EEPN-induced constraints on LO linewidth have been experimentally characterized in [2] on quadrature-phase-shift-keying (QPSK) signals, and simulation results in [3] highlighted tighter requirements for higher modulation formats such as 16 and 64QAM.