Abstract: The principles of laser coherent beam combination that can enhance the output power and improve the beam quality are introduced. The developments of coherent beam combining technique are reviewed and discussed. Two beam combining approaches that respectively based on active phase control and passive phase control are compared. Based on the master oscillator power amplifier (MOPA), the active phase control can obtain a neardiffraction limited, stable and high brightness farfield laser beam. As a result, the active phase control is considered to be a technical support for a long distance, high rate data space optical communication system. It provides valuable information on the trends of laser coherent beam combination technology and has some important significance for space optical communication.

Key words: space optical communication, coherent laser beam combination, active phase control, passive phase control