Patent ID: 7684697

Claim:
An optical signal quality monitoring circuit comprising: photoelectric conversion means for converting an input optical signal to an electrical signal; sampling means for sampling and converting the electrical signal with any given repetition frequency f 1 to digital sampling data by an analog to digital conversion; and signal processing means for correcting and evaluating an averaged Q value based on correction factors obtained in advance according to a change in the signal bit rate of the optical signal, wherein the signal processing means: calculates, by using the sampling data, averages μ 0 and μ 1 and standard deviations σ 0 and σ 1 for two distributions of signal amplitude values that are mark part and space part, and calculates the averaged Q value as an optical quality parameter of the optical signal using the calculated averages μ 0 and μ 1 and standard deviations σ 0 and σ 1 .