Patent ID: 8655170

Claim:
An optical signal-to-noise ratio (OSNR) monitor device, comprising: an optical receiver including a delay interferometer, which inputs a phase modulated optical signal in accordance with a given bandwidth and outputs two optical signals and causes the optical signals to interfere with each other, optical detectors, which output currents in accordance with optical powers of the optical signals output from the interferometer, and an optical filter that performs filtering on optical signals that have been subjected to a demultiplexing in accordance with a bandwidth smaller than the given bandwidth; an optical power monitor configured to obtain the optical powers of the optical signals received by the optical detectors included in the optical receiver; and an OSNR calculator configured to calculate an optical signal-to-noise ratio in accordance with the optical powers obtained from the optical power monitor and a reception bandwidth, wherein the bandwidth that has been set to the optical filter is obtained by a bandwidth monitor included in the OSNR monitor device.