Patent ID: 7146099

Claim:
A method of analyzing signal and noise characteristics of an optical communications signal, comprising: establishing a threshold; comparing the optical communications signal to the threshold to generate a comparison result signal, the comparison result signal having a predetermined binary value when respective amplitudes of the optical communications signal and the threshold satisfy a predetermined comparison relationship; counting, over a count interval substantially longer than a signaling period of the optical communications signal, a count of sampling instants at which the comparison result signal has the predetermined binary value, the count being stored in association with the threshold; repeating the threshold establishing, comparing, and counting for each of a range of thresholds corresponding to an expected range of amplitudes of the optical communications signal, the count and threshold from each repetition being stored in mutual association, the stored counts and thresholds from all repetitions collectively representing a function N(V T ) relating a count variable N to a threshold variable V T over the range of thresholds; calculating, from the stored counts and thresholds, a derivative function dN/dV T of the function N(V T ); and utilizing predetermined parameters of the derivative function dN/dV T to calculate two half widths of two curve portion of the derivative function dN/dV T , the half-widths being used to calculate a signal quality for the optical communications signal, the optical communications signal being adjusted according to the calculated signal quality.