Patent ID: 6839518

Claim:
WDM (Wavelength Division Multiplexing) transmission device comprising: a level adjustment unit adjusting levels of optical signals having different wavelengths; a multiplexer multiplexing the optical signals and outputting a multiplexed optical signal; an amplifier amplifying the multiplexed optical signal; and a monitor unit monitoring a level of the multiplexed optical signal to be applied to the amplifier and a level of an output signal of the amplifier and controlling the level adjustment unit with the levels of the multiplexed optical signals to be applied to the amplifier falling within a predetermined level range in which the amplifier operates normally, the monitor unit comprising a first decision unit determining whether the level of the multiplexed optical signal applied to the amplifier falls within a first target level range, and a second decision unit determining whether the levels of the optical signals having the different wavelengths included in the output signal of the amplifier fall within a second target level range, wherein the monitor unit updates the second target level if the input of the amplifier fails to fall within the first target level range.