Patent ID: 6532087
Filing Date: 2003-03-11
Classification: H04B

Abstract:
A circuit for monitoring the Q-factor of a plurality of main signals being simultaneously transmitted across a fiber optic line, the circuit comprising:an optical tap for tapping the fiber optic line to provide a plurality of tapped signals corresponding to the plurality of main signals; a filter for selecting one of the plurality of tapped signals; and a Q-detection circuit for determining the Q-factor of the selected signal, wherein the Q-detection circuit includes: a first variable attenuator for attenuating the selected signal in response to a first attenuator control signal; a first optical-to-electrical converter for converting a first portion of the attenuated signal into an electrical data signal; a second optical-to-electrical converter for converting a second portion of the attenuated signal into a first power indication signal; a decision circuit for detecting high and low data bits in the electrical data signal based on a plurality of threshold voltage signals, and for providing decision signals indicative of the results of these determinations; an error monitoring circuit for receiving the decision signals, determining the bit error rate of the incoming optical signal for the plurality of threshold voltages, and providing bit error rate signals; and a microprocessor for receiving the power regulation signal and the bit error rate signals, and for generating a first attenuator control signal and a plurality of threshold voltage signals, wherein the variable attenuator operates to attenuate the selected signal such that it is at an optimal input level for the operation of the first optical-to electrical converter, wherein the microprocessor determines an optimal bit error rate and an optimal Q-factor for the selected signal based on the bit error rates of the selected signal for the plurality of threshold voltages.