Patent ID: 7437069

Claim:
An automatic power restoring method, in which, in an optical communication system which includes an optical amplification medium on an optical transmission path connecting between an optical transmitting station and an optical receiving station, for transmitting a main signal light sent out from the optical transmitting station to the optical receiving station via the optical transmission path while amplifying the main signal light, a power state at an occurrence of line fault in which the power of a light output from the optical transmitting station or the optical receiving station to the optical transmission path is suppressed to a predetermined level or lower, is restored to a power state at a time of normal operation according to a detection of continuity by dissolution of said line fault, comprising: setting a wavelength of a pilot signal light corresponding to a wavelength where a loss is the smallest for loss wavelength characteristics obtained by combining loss wavelength characteristics of an optical transmission medium used for a portion other than the optical amplification medium of said optical transmission path and loss wavelength characteristics of said optical amplification medium in a state at the occurrence of line fault, to send out said pilot signal light at the predetermined power level or lower from one of the optical transmitting station and the optical receiving station to the optical transmission path at least when the line fault occurs; and detecting continuity, by receiving at the other station the pilot signal light sent out to said optical transmission path, to restore the power state at the occurrence of line fault to the power state at the time of normal operation.