Method and apparatus for monitoring a failure of an optical signal

摘要

In an optical signal failure monitoring apparatus for monitoring a failure of an optical signal of a signal wavelength ( lambda 1), a calculating circuit (703) calculates an optical S/N ratio of a power of the optical signal to another power of a spontaneous emission light of a different wavelength ( lambda N+1) which is different from the signal wavelength. A detecting circuit (704) detects the failure of the optical signal to produce a failure detection signal when the optical S/N ratio is less than a predetermined value. Preferably, the calculating circuit calculates, as the optical S/N ratio, a difference given by subtracting the power of the spontaneous emission light from the power of the optical signal. Detection of the power of the optical signal may be carried out instead of detection of the optical S/N ratio in the calculating circuit. In this case, the detecting circuit detects the failure of the optical signal and produces the failure detection signal when the power of the optical signal is less than the predetermined value.