In conclusion, the advantages of coherent optical DSP in fiber-optic networks, encompassing improved signal integrity, enhanced spectral efficiency, better noise resilience, and support for advanced modulation formats, lead to significant improvements in network performance and. In conclusion, the advantages of coherent optical DSP in fiber-optic networks, encompassing improved signal integrity, enhanced spectral efficiency, better noise resilience, and support for advanced modulation formats, lead to significant improvements in network performance and. Abstract: The drive for higher performance in optical fiber systems has renewed interest in coherent detection. We review detection methods, including noncoherent, differentially coherent, and coherent detection, as well as a hybrid method. By moving beyond simple power measurement, coherent systems enable sophisticated recovery of the signal waveform, which drives faster internet speeds and high-resolution. Coherent detection is a revolutionary technique in optical communications that has transformed the way data is transmitted over fiber optic networks. At its core, coherent detection involves the mixing of the incoming optical signal with a locally generated optical signal, known as a local. While direct detection works well for short-distance links, it has limitations in terms of capacity and sensitivity. It cannot efficiently use phase information and is more vulnerable to signal impairments such as dispersion. Dispersion β an effect caused by the fact that light waves travel.