Coherent optical communication is an important technique which improves the sensitivity of receiver and develops a large-capacity and high-rate laser communication system. An optical hybrid is one of the key components of coherent receiver, which mixes the signal with the local oscillator beams and bridges them to detector for information processing. In this paper, the optical hybrids developed in recent twenties years are surveyed. The principles, configurations and properties of different optical hybrids are introduced and the key techniques are analyzed.