Coherent optical communication is a field of research and engineering focused on data transmission techniques utilizing the wave properties of light, specifically the phase and/or polarization of the optical carrier, in addition to intensity. This approach employs sophisticated modulation schemes and requires a local optical oscillator at the receiver to coherently mix with the incoming signal, enabling detection with enhanced sensitivity and spectral efficiency compared to direct detection methods. It is significant for enabling high-capacity, long-haul telecommunication systems by maximizing the information carried per unit of optical bandwidth.