Patent ID: 7443574

Claim:
An optical transmission system, comprising: an optical nonlinear element having nonlinear input/output characteristics and reproducing an optical signal; a power detector photoelectrically converting an optical signal reproduced by said optical nonlinear element into an electrical signal, and detecting a power of a specific frequency component obtained from the electrical signal by the photoelectric conversion; and a variable output device amplifying or attenuating the optical signal inputted to said optical nonlinear element in response to a detection result by said power detector; wherein said power detector comprises: a photo detector converting the optical signal reproduced by said optical nonlinear element to the electrical signal; a filter retrieving the specific frequency component from the electrical signal obtained by said photo detector; and a power measuring device measuring the power of the specific frequency component retrieved by said filter; wherein said power detector detects power of a bit rate frequency component of the inputted optical signal; and the optical transmission system further comprising: a control circuit controlling said variable output device such that the power of the bit rate frequency component becomes minimum, based on a detection result by said power measuring device; and wherein said control circuit makes a gain of said variable output device increase/decrease periodically in a minute range to perform gain control of said variable output device in response to variation of the power of the bit rate frequency component associated with the minute variety of the gain.