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.