Optical fiber communication system consists of five parts: electrical terminal, optical transmitter, optical cable, optical repeater and optical receiver.

The function of electric transmitter is to process signals from information sources, such as analog-to-digital (A/D) conversion and multiplexing. It is a universal electronic communication equipment. At the transmitter, the electronic terminal converts analog information (such as voice) into analog/digital, thus realizing ETDM. Light source devices in optical transmitter, such as semiconductor laser (LD) and semiconductor light emitting diode (LED), are modulated by digital signals after electric modulation, and their function is to convert electrical signals into optical signals, that is, to complete electric/optical (E/O) conversion. Then the optical signal is coupled into the optical fiber and transmitted to the other side. At the receiving end, there are photodetectors in the optical receiver, such as photodiodes PIN and APD, whose function is to restore the optical signal from the optical fiber into an electrical signal, and then input it into the electrical receiver after amplification, shaping, regeneration and restoration. The electronic terminal performs digital-to-analog conversion to restore the electrical signal to the original analog information. In the case of long-distance communication, it is necessary to add several optical repeaters on the transmission line, whose function is to amplify and shape the weak optical signals attenuated and distorted by long-distance optical fibers, and then generate optical signals with a certain intensity and continue to send them to the distance to ensure good communication quality.