To suppress the deterioration of a CN ratio of a pilot signal even when the number of wavelength of an optical signal which is inputted to a light space switch is increased by replacing M input converging devices with a pieces of (b) input converging devices and one (a) input converging device, branching a part of an output signal of the (b) input converging devices and supervising a pilot signal that is superimposed on the optical signal.
The functions of four input converging devices 31 and 32 are respectively divided into two input converging devices 31-1 to 31-3 and 32-1 to 32-3, and branching devices 41-1 to 42-2 are arranged before the devices 31-3 and 32-3. Optical signals which are outputted from 1×2 light switches 21 and 22 to an output port 61 are branched from an output of the device 31-1, and a pilot signal which is superimposed on the optical signal is supervised by a connection supervisory circuit 51-1. Similarly, optical signals are branched from the devices 31-2 to 32-2 and connection supervisory circuits 51-2 to 52-2 supervise pilot signals. With this, the wavelength multiple number of an optical signal that is a supervisory object becomes two wavelength at most and the deterioration of a CN ratio of a pilot signal can be suppressed.
KOGA MASABUMI
SATO KENICHI
