The adoption of optical fiber communication is a major innovation in the history of the communication field, and its development has gone through three generations in a short period of time. They are:Shortwave multimode optical fiber, long wavelength multimode optical fiber with long wavelength single mode fiber, announced in some western developed countries have banned the construction of the cable line, has been advocated to develop the optical fiber communication technology, and in the domestic communication technology has been in the actual application, it is mainly used for mobile telephone trunk line, gets the play of incisively and vividly fully in the trunk.The birth of coherent optical communication technology can realize the effect of large capacity, high speed and long distance transmission of optical fiber communication.Coherent optical communication adopts heterodyne detection method. When setting the vibrator, the optical signal transmitted by optical fiber and the laser I.D are added to the photoelectric detector, resulting in the appearance of differential frequency electrical signals in the photoelectric conversion process. Finally, the electrical signals required to be transmitted by the sender are obtained after the Chinese side and demodulation.

With the application of heterodyne detection in radio communication communication, the problem of high frequency amplification and filtering has been solved effectively.Through the introduction of coherent modulation technology, the frequency and phase information of radio waves are fully utilized, so that the ability of radio communication system is greatly enhanced.The coherent modulation is to use the transmitted signal to change the frequency, amplitude and phase of the optical carrier, which should determine the phase and frequency of the optical signal.The heterodyne detection method is adopted in order to obtain the IF signal, the input signal light needs to be effectively mixed with the laser generated by the local oscillation in the optical mixer.Because of the characteristics of coherent optical communication technology has high sensitivity and excellent selectivity, it can be made into a slightly remote distance and relatively large capacity of the trunk line network, and the communication technology has been very good application in the CATV system.With the development of microelectronics and optical communication, the application and development of coherent optical communication technology will be more and more extensive.