Patent ID: 7877019

Claim:
An apparatus comprising: an optical amplifier for amplifying an optical signal having data modulated thereon according to a DPSK modulation format; an optical band pass filter coupled to said optical amplifier for receiving said optical signal; a demodulator coupled to said amplifier filter for demodulating said optical signal, said demodulator being configured to split said optical input signal onto first and second arms and provide first and second optical outputs; first and second photo detectors, said first photodetector being configured for providing a first electrical output in response to said first optical output being imparted thereon, said second photodetector being configured for providing a second electrical output in response to said second optical output being imparted thereon; an integrated clock and data recovery circuit coupled to said first and second electrical outputs, said integrated clock and data recovery circuit being configured to provide a data output representative of said data modulated on said optical signal and said integrated clock and data recovery circuit being configured to provide a separate signal level detector (SLD) output representative of a signal level of at least one of said first and second electrical outputs and a separate negative signal level detector (NSLD) output representative of a signal level of at least one of said first and second electrical outputs; a differential amplifier configured to receive said SLD and NSLD outputs and provide a differential amplifier output; and a controller for providing an amplifier setting signal in response to said differential amplifier output for controlling a gain of said amplifier.