| 摘要 |
The power level of a wavelength division multiplexed optical signal is detected by a detection unit. When the power level of the optical signal detected by the detection unit is equal to or lower than a first threshold, the coupling direction of an attenuation unit for controlling the coupling direction for the ports of the optical signal is controlled in the direction orthogonal to the array direction of the ports. When the power level of the optical signal exceeds a second threshold, the coupling direction of the attenuation unit is controlled in the array direction of the ports.
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