Patent ID: 8126331

Claim:
A wavelength division multiplexing transmission device, comprising: a plurality of ports where a wavelength division multiplexed optical signal is input and output; a wavelength demultiplexing unit demultiplexing the wavelength division multiplexed optical signal; an attenuation unit controlling a coupling direction for the ports of a wavelength demultiplexed optical signal of each wavelength and controlling an amount of attenuation; a detection unit detecting a power level of an optical signal at an output terminal; and a control unit controlling the coupling direction of the attenuation unit in a direction orthogonal to an array direction of the ports when the detection unit detects that a power level of the optical signal reaches a first threshold or lower, and controlling the coupling direction of the attenuation unit in the array direction of the ports when the detection unit detects that the power level of the optical signal exceeds a second threshold.