Patent ID: 6351322
Filing Date: 2002-02-26
Classification: H04B

Abstract:
A Q detection circuit, comprising:a first variable attenuator for attenuating a received optical signal in response to a first attenuator control signal; a first optical-to-electrical converter for converting a first portion of the attenuated optical signal into an electrical data signal; a second optical-to-electrical converter for converting a second portion of the attenuated optical 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 received optical signal for the plurality of threshold voltages, and providing bit error rate signals; and a microprocessor for receiving the power indication signal and the bit error rate signals, and for generating the first attenuator control signal and the plurality of threshold voltage signals, wherein the first variable optical attenuator operates to attenuate the received optical 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 received signal based on the bit error rates of the received optical signal for the plurality of threshold voltages.