Coherent optical receiver

A coherent optical receiver that processes received signal light by a coherent reception system, comprising:

• a local oscillator light generating section that generates local oscillator light having orthogonal polarization components in which the optical frequencies are different to each other;
• a combining section that combines received signal light and local oscillator light output from said local oscillator light generating section;
• a photoelectric conversion section that converts a light combined in said combining section into an electrical signal;
• an AD conversion section that converts the electrical signal output from said photoelectric conversion section into a digital signal;
• a digital computing section that uses a digital signal output from said AD conversion section, to execute computation processing in order to estimate data information included in said received signal light;
• and
• a data discrimination section that executes discrimination processing of received data, based on a computation result of said digital computing section,
• wherein the difference in the optical frequencies between the orthogonal polarization components of said local oscillator light are smaller than two times the band width of said received signal light, and larger than a light source spectrum line width of said received signal light and a light source spectrum line width of said local oscillator light, and
• in said local oscillator light generating section, a ratio of intensity between said orthogonal polarization components is variable, and
• said local oscillator light generating section comprises:
• a light source;
• an orthogonal polarization component section that changes an output light from said light source into the local oscillator light having orthogonal polarization components which have different frequencies;
• a monitor circuit that monitors the ratio of the intensity between the orthogonal polarization components;
• and
• an intensity ratio control circuit that controls the ratio of the intensity between the orthogonal polarization components depending on a monitor result of said monitor circuit and a calculation result of said digital computing section.