Patent ID: 7283742

Claim:
An optical signal judging system for judging an optical signal outputted from an optical switch which selectively outputs any one of input optical signals, comprising: a converting unit converting at least two optical signals branching off from an optical signal source into optical signals having wavelength bands differing from each other, and thus outputting the at least the two optical signals to said optical switch, wherein said optical switch outputs any one of the at least two optical signals so converted as to have the wavelength bands differing from each other, which have been inputted from said converting unit; a control unit selecting any one of the at least two optical signals and performing switching-control of said optical switch so that the selected optical signal is outputted; a filter unit including a first wavelength band filter having a fixed transmission wavelength band transmitting one of the at least two optical signals and a second wavelength band filter having a fixed transmission wavelength band transmitting the other of the at least two optical signals; a light receiving unit including a first light receiving device receiving the optical signal outputted from said optical switch and transmitted through said first wavelength band filter, and a second light receiving device receiving the optical signal outputted from said optical switch and transmitted through said second wavelength band filter; a judging unit checking the wavelength band of the optical signal selected by said control unit with a result of receiving the optical signal received by the first and the second light receiving devices, and judging the wavelength band of the optical signal outputted from said optical switch; and a detecting unit detecting abnormality of said optical switch when the optical signal to be outputted from the optical switch by the control unit is not received by any one of the first light receiving device and the second light receiving device.