development of optical fiber communication technology rapid development, many scholars put forward " all-optical network" concept, the intention is to signal in the form of light across the entire network, directly in optical domain signal transmission, regeneration and switching / routing, the intermediate without any photoelectric conversion, to achieve full transparency realize, at any time, anywhere, the transmission of any format ideal target signal. But because the optical device technical

limitations, the present all-optical network coverage is also very small, to expand the network coverage, must through the photoelectric conversion to eliminate the optical signal in the transmission process of accumulated damage ( attenuation, dispersion, nonlinear effect), network maintenance, control and management. Therefore, what is now known as " network" is made of high performance photoelectric conversion device is connected to numerous optical transparent subnet collection, is about" ITU-T optical transport network " of the concept of popular opinion.

The three optical fiber communication system.

( 1) optical transmitter