Patent ID: 8050351

Claim:
An optical communications system adapted to operating in two polarization states of light for transmitting phase shift keying modulated data, comprising: a light source; a first modulator for modulation of an optical signal, the modulator having a first automatic feedback control, the modulator receiving an optical signal from the light source and producing a first QPSK optical signal; a first coherent optical receiver, the first coherent optical receiver mixing the first QPSK optical signal with a first reference signal from a local oscillator, the coherent received demodulating data encoded in the first QPSK optical signal; wherein the first automatic feedback control including a first low speed optical detector to detect at least a portion of the first QPSK optical signal; a first spectral power detector to detect a power of a first RF spectral component of the first QPSK optical signal; and a first digital signal processing (DSP) unit receiving the signal from the first spectral power detector, the first DSP unit controlling a first phase shifter of the first modulator to minimize the signal from the first spectral power detector, a second modulator for modulation of an optical signal with a second automatic feedback control, the modulator receiving an optical signal from the light source having a second polarization state being orthogonal to the first polarization state and producing a second QPSK optical signal; a polarization combiner to combine the first and the second QPSK optical signals for transmitting over a communication link, a second coherent optical receiver, the coherent optical receiver mixing the second QPSK optical signal with a second signal from a local oscillator having the same polarization state as the second QPSK optical signal; wherein the second feedback control including a second low speed optical detector to detect at least a portion of the second QPSK optical signal; a second spectral power detector to detect a power of a second RF spectral component of the second QPSK optical signal; a second digital signal processing (DSP) unit receiving the signal from the second spectral power detector, the DSP unit controlling a second phase shifter of the second modulator to minimize the signal from the second spectral power detector.