# Equalization Enhanced Phase Noise in Coherent Receivers: DSP-Aware Analysis and Shaped Constellations

## TL;DR

This paper analyzes equalization-enhanced phase noise (EEPN) in coherent receivers, showing how DSP algorithms and shaped constellations influence EEPN impact and system performance, with both simulations and experiments.

## Contribution

It provides a numerical approach to predict EEPN effects considering phase recovery algorithms, relaxing previous constraints on laser phase noise in coherent systems.

## Key findings

- Blind phase search mitigates EEPN effects.
- Taking EEPN into account relaxes phase noise constraints.
- Experimental validation confirms simulation predictions.

## Abstract

We revisit the analysis of equalization-enhanced phase noise (EEPN) arising in coherent receivers from the interaction between the chromatic dispersion compensation by an electronic equalizer and the phase noise of the local oscillator. Through numerical simulations we highlight EEPN characteristics and investigate its impact on the behavior of the carrier phase recovery algorithm. We show that the blind phase search, which is usually used in practice to recover the carrier phase, partially mitigates the EEPN. We detail a numerical approach to predict the system performance including the phase recovery algorithm, and show that taking into account EEPN characteristics relaxes the constraint on the system laser phase noise given by previous pessimistic analytical models. We present experimental validations of our claims, and address future advanced transoceanic systems using 98 GBd probabilistically shaped QAM formats.