So-called optical fiber communications, is using fiber to transmit light waves to carry information to achieve the purpose of communication. To make the optical information carrier, must be modulated, detected in receiving information from light. However, because of limited State-of-the art, optical frequency modulation and phase modulation is still confined to the lab, the practical level has not been reached, so the current intensity modulation and direct detection methods used (IM-DD). Since the current light source device and optical receiving devices for nonlinear is serious, so low linearity requirements for optical devices in digital optical in optical fiber communication dominate.

Digital optical fiber communication system by optical transmitters, optical fiber and optical receiver. Transmitter transmitter and receiver of information (voice) for a/d conversion, converted the digital signal modulation transmitter light source devices in LD, LD will issue a message carried by light waves. That is, when the digital signal is "1", the light source device sending a "mark" light pulse; when the digital signal is "0", the light source device to send an "empty" (no light). After low attenuation optical fiber transmission, the light reaches the receiver. At the receiver, optical receiver converts digital signals detected from optical to electrical converter, Terminal d/2 conversion machine, back into the original message. Just completed a communication process.