Patent ID: 7421210

Claim:
An optical transmission method comprising: outputting an output light having first and second polarization components, the first and second polarization components being orthogonal to each other; generating a phase-modulated signal light by phase-modulating the first polarization component of the output light according to a transmission data to output the generated phase-modulated signal light and the second polarization component into an optical transmission line in an orthogonal polarization state; coupling the phase-modulated signal light and the second polarization component input from the optical transmission line in the same polarization direction so as to convert the phase-modulated signal light into an intensity-modulated signal light; converting the intensity-modulated signal light into an electric signal; and restoring the transmission data from the electric signal; restoring comprises computing a bit error rate of a received data and wherein the coupling to convert the phase-modulated signal light into the intensity-modulated signal light comprises controlling a polarization direction of a light input from the optical transmission line so as to decrease the bit error rate according to the computed bit error rate.