Patent ID: 7365903

Claim:
An apparatus for all-optically controlling gain and gain flattening, the apparatus comprising: a first amplifier configured to amplify a received optical signal, output the amplified signal along an optical transmission path, and automatically control a gain through a first lasing light feedback loop; a fixed gain flattening unit configured to receive the amplified optical signal from the first amplifier and compensate for the gain according to a wavelength of the received optical signal; and a second amplifier configured to amplify the optical signal input from the fixed gain flattening unit and automatically control the gain through a second lasing light feedback loop; wherein the first amplifier comprises: a first amplifying unit that amplifies the optical signal received by the first amplifying unit; a first lasing light coupler that couples a lasing light into the first feedback loop from the optical signal transmission path; and a first lasing light power coupler that feeds lasing light formed by the feedback loop back into the optical transmission path; wherein the second amplifier comprises: a second amplifying unit that amplifies the optical signal received by the second amplifying unit; a second lasing light coupler that couples a lasing light into the second feedback loop from the optical signal transmission path; and a second lasing light power coupler that feeds lasing light formed by the second feedback loop back into the optical signal transmission path; wherein the fixed gain flattening unit comprises a variable attenuator that adjusts the intensity of the output signal from the first amplifier; and wherein each of the lasing light power couplers and the lasing light couplers includes an optical power splitter in combination with a band pass filter.