Describe the differences between direct detection and coherent detection in optical communication systems.

Direct detection and coherent detection are two distinct methods for receiving optical signals in fiber optic communication systems. Direct detection is the simpler and more traditional approach. In direct detection, the receiver directly measures the intensity of the received light signal. A photodiode converts the optical power into an electrical current, which is then amplified and processed to recover the transmitted data. Direct detection is sensitive only to the amplitude (intensity) of the light. Coherent detection is a more advanced technique that offers improved performance and flexibility. In coherent detection, the received optical signal is mixed with a locally generated laser signal, called the local oscillator (LO). This mixing process creates an intermedi....