Optical modules serve as the "translators" of fiber-optic networks, enabling seamless electrical-to-optical (E/O) and optical-to-electrical (O/E) conversion. With advancements in PAM4, DSP, and silicon photonics, they are driving the evolution of 5G, cloud computing, and AI. This document provides a tutorial for Optical Transport Network standards and their applications. 798 —that provides an efficient way to transport, switch, and multiplex different services onto high-capacity wavelengths across the optical network. Average optical power refers to the optical power outputted by the optical module's transmitter under normal working conditions, which can be understood as the intensity of light.