Erbium-doped fiber amplifier with automatic gain control

A coherent optical communication transmission system, comprising:

• a plurality of light sources and local oscillators connected to mixers to provide a plurality of mixed light signals,
• an optical combiner connected to combine the plurality of mixed light signals into a combined light signal,
• a laser connected to said combiner, said laser being operative to provide a carrier for the combined light signal,
• a laser cavity gain controlled EDFA connected to amplify the combined light signal, wherein said laser cavity gain controlled EDFA includes an EDFA connected to receive mixed light signals and a laser cavity connected so as to provide the EDFA with negative feedback and thereby clamp the gain of said EDFA, the lasing wavelength of said laser cavity being selected such that the saturation power at the laser wavelength is less than that at the signal wavelengths,
• a detector connected to detect the amplified combined light signal,
• a divider connected to said detector to receive and divide the amplified combined light signal into a plurality of mixed light signals, and
• a plurality of mixers and local oscillators connected to unmix said mixed light signals to recover the plurality of light sources.