The optical receiver adds two types of noise namely thermal noise and shot noise. This application note provides an in-depth analysis of the complete receiver optical sensitivity and the potential power penalties related to the accumulation of random noise and inter-symbol interference (ISI) in both amplitude and timing. Ultimately, the noise influence on the signal will determine the system sensitivity. The challenge is to find a way to determine the. In the design of an optical receiver, it is vital that the module is capable of converting and shaping the optical signal while meeting or surpassing the maximum BER.