Patent ID: 7792430

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 line fault, comprising: setting a pilot signal light in a wavelength band, which is shifted to a long wavelength side by approximately 100 nm from a wavelength band of the main signal light, to send out, when a line fault occurs, the main signal light from the optical transmitting station to the optical transmission path, and also to send out the pilot signal light at the predetermined level or lower from one of the optical transmitting station and the optical receiving station to the optical transmission path, in which the main signal light is utilized as a pumping light; and detecting continuity, by receiving at the other station the pilot signal light sent out to the optical transmission path, to restore the power state at the occurrence of line fault to the power state at the time of normal operation.