Patent ID: 8824902

Claim:
An optical receiver comprising: an optical to electric converter that converts a received optical signal into an analog electric signal; an analog to digital converter that converts the analog electric signal obtained by the optical to electric converter into a digital signal; a digital signal processor that performs wave shaping on the digital signal to produce a shaped signal; an information extract circuit that extracts information related to loss or deterioration of the optical signal from a signal propagating from the analog to digital converter to the digital signal processor or a signal in the digital signal processor; and a judging circuit that judges, based on the information extracted by the information extract circuit, whether the optical signal is lost or deteriorated by comparing the information with a threshold, the information including at least one of: a number of times that an amplitude of the digital signal exceeds a threshold within a predetermined period, a light spectrum peak value obtained from a fixed pattern of the received optical signal that is received by the optical to electric converter, a sensitivity of detecting a sampling phase shift when synchronizing a sampling phase of the digital signal, an amount of the sampling phase shift when synchronizing the sampling phase of the digital signal, a peak value of a constellation distribution of the shaped signal, a peak width of the constellation distribution of the shaped signal, and a signal quality value of the constellation of the shaped signal, wherein the threshold has a first value for judging deterioration of the optical signal and a second value for judging loss of the optical signal, the second value being different from the first value.