Patent ID: 7796894

Claim:
An optical wavelength division multiplexing (WDM) communication system, comprising: a fiber transmission line that receives a plurality of WDM optical signals at different WDM wavelengths; an optical circulator having a first port coupled to the fiber transmission line to receive the WDM optical signals, a second port to output the received WDM optical signals and a third port to output light received at the second port; a WDM demultiplexer coupled to the second port of the optical circulator to separate WDM optical signals output by the second port into separated WDM optical signals along different optical paths; and a plurality of optical conditioning modules respectively coupled in the different optical paths, each optical conditioning module reconditioning a respective WDM optical signal and direct the reconditioned WDM optical signal back to the WDM demultiplexer which combines reconditioned WDM optical signals from the separate optical paths into the second port of the optical circulator which outputs the reconditioned WDM optical signals at the third port, each optical conditioning module comprising: a polarization controller coupled in a respective optical path for a respective WDM optical signal to control polarization of the WDM optical signal in response to a control signal; a polarization beam splitter placed in the optical path downstream from the polarization controller to transmit light in a first polarization in the WDM optical signal as a first optical signal and to reflect light in a second polarization orthogonal to the first polarization in the WDM optical signal as a second optical signal; a first optical detector to receive at least a portion of light of the first optical signal to produce a first detector signal; a second optical detector to receive at least a portion of light of the second optical signal to produce a second detector signal; a partial reflector located in one an optical path between the polarization beam splitter and one of the first and second optical detectors to reflect light back to the polarization beam splitter which directs the reflected light from the partial reflector to pass through the polarization controller to the WDM demultiplexer as a reconditioned WDM optical signal; and a control circuit coupled to receive the first and second detector signals to produce the control signal to the polarization controller based on the received first and second detector signals to reduce noise and polarization mode dispersion in the reconditioned WDM optical signal.