Patent ID: 8774635

Claim:
An optical gain control system to translate a received information-modulated optical signal, having time-varying optical intensity fluctuations, to a substantially constant-intensity optical signal having a time-varying optical signal-to-noise ratio that represents the modulating information, comprising: a first optical amplifier to amplify the received optical signal by a first gain level and output a corresponding first amplified optical signal; a first optical filter to filter the first amplified optical signal; a variable optical attenuator to controllably attenuate the filtered first amplified optical signal and output a corresponding attenuated optical signal; a second optical amplifier to amplify the attenuated optical signal by a second gain level and output a corresponding second amplified optical signal; a second optical filter to extract an optical signal from the second amplified optical signal; at least one detector to detect an optical intensity of one or more of the received optical signal, the first amplified optical signal, the filtered first amplified optical signal, the attenuated optical signal, the second amplified signal, the extracted optical signal, and noise within a filtered portion of the second amplified signal; a controller to control at least the variable optical attenuator to reduce time-varying fluctuations in the detected optical intensity such that the extracted optical signal corresponds to the substantially constant-intensity optical signal: and a control loop to clamp one or more of the first and second gain levels when a detected optical intensity reaches a threshold.