Patent ID: 8494361

Claim:
A quality monitoring apparatus, comprising: an optical splitter for splitting a binary intensity-modulated light signal to be monitored into three or more light signal beams; a delaying interferometer for making one of the light signal beams interfere with a light signal obtained by delaying the one light signal beam by a predetermined delay time to produce constructive and destructive interference signals to output one of the constructive and destructive interference signals; a photoelectric converter for converting light signal beams directly supplied thereto from said optical splitter and a light signal emerging from said delaying interferometer into electric signals; a filter bank including band-pass filters for passing a frequency component of an electric signal fed from said photoelectric converter, the frequency component corresponding to a bit rate of the light signal to be monitored, and a smoothing filter for smoothing an electric signal fed from said photoelectric converter; an amplifier for amplifying outputs from said band-pass filters to a level enabling a subsequent detection; detector circuitry for detecting intensities of electric signals from said amplifier and an intensity of a smoothed electric signal; and an arithmetic circuit for setting the intensity of the detected, smoothed electric signal as a reference, and calculating the intensities of the detected, amplified signals relative to the reference to determine wavelength dispersion and optical SNR (signal-to-noise ratio) of the light signal to be monitored or a tendency of change in the wavelength dispersion and optical SNR based on the calculated relative intensities, said detector circuitry comprising: a first signal intensity detector on a first branch line over which the light signal beam from said splitter passes for detecting the intensity of the band-pass filtered, amplified electric signal originated from the light signal beam; a second signal intensity detector on a second branch line over which the light signal beam from said splitter passes for detecting the intensity of the electric signal band-pass filtered and amplified after emerging from said delaying interferometer; and a power intensity detector on a third branch line over which the light signal beam from said splitter passes for detecting the intensity of the smoothed electric signal derived from the light signal.