Patent ID: 7463829

Claim:
An optical transmission apparatus for outputting wavelength-division multiplexed signal lights received together with a supervisory signal light to an optical transmission path of a next section with a predetermined optical power, comprising: first means for separating the supervisory signal light from the received wavelength-division multiplexed signal lights and detecting the power of the supervisory signal light; second means for detecting the power of the wavelength-division multiplexed signal lights after the separation of the supervisory signal light; a gain control type optical amplifier for amplifying said wavelength-division multiplexed signal lights; an optical attenuator variable in the extent of attenuation for adjusting the power level of the wavelength-division multiplexed signal lights outputted from said optical amplifier; and a monitor and control unit for controlling said optical amplifier to keep a constant gain and controlling the extent of attenuation of said optical attenuator so that the output power of the wavelength-division multiplexed signal lights has a predetermined target value, wherein: said monitor and control unit restrains said automatic output level control by said optical attenuator when the power of said supervisory signal light detected by said first means is fluctuating within a permissible range and fluctuations in the wavelength-division multiplexed signal light power detected by said second means has deviated from its permissible range.