On the Enhancement of Unamplified Optical Coherent Systems

With coherent optical systems expanding their use to short-reach applications, it is imperative to achieve a cost and power-efficient solution that allows massive deployment. As increasingly higher data rates are required for shorter distances, the standardization of 400ZR and 800G for coherent transceivers is motivating the pursuit of unamplified systems, giving rise to new challenges, particularly due to the inherent peak-power constraint. In this paper, we discuss methods to improve the performance of unamplified coherent systems; particularly, we show the impact of pulse shaping and how it might undermine the system performance, and show how new advanced methods such as probabilistic constellation shaping can be used within these systems.