Patent ID: 8805188

Claim:
A polarization-multiplexed optical transmission system comprising: a polarization-multiplexed optical transmitter that: i) includes two optical modulators and a polarization beam combiner, ii) modulates input light input to the two optical modulators using mutually different multilevel information signals being one of one-dimensional and two-dimensional to generate an optical multilevel signal, and iii) allows the polarization beam combiner to multiplex the optical multilevel signal into mutually orthogonal polarizations for transmission, wherein the polarization-multiplexed optical transmitter supplies a specified frequency difference to a center frequency of an optical multilevel signal for the mutually orthogonal polarization components; and a polarization-multiplexed optical receiver including: an adaptive polarization splitting circuit for adaptively separating two orthogonal polarization components from a polarization-multiplexed signal; and two sets of demodulation parts for demodulating two separated polarization components, wherein the polarization-multiplexed optical receiver detects a frequency difference component in two received polarization components and identifies or separates a multiplexed original orthogonal polarization component based on a detected frequency component, center frequencies of each of the mutually orthogonal polarization components: i) are first matched, and ii) are subsequently shifted by different amounts with respect to the matching center frequencies, and the specified frequency difference is approximately 20 % or less of an entire bandwidth occupied by a transmitted optical signal.