Delayed interferometer and optical receiver

An optical receiver comprising:

• a branching unit that branches an optical signal modulated by a phase modulation system into a first optical signal and a second optical signal;
• a guiding unit that acquires the first optical signal branched by the branching unit, guides the first optical signal in a first optical path to delay the first optical signal by one bit when a polarization direction of the acquired first optical signal is the first direction, and guides the first optical signal in a second optical path having an optical distance shorter than that of the first optical path when the polarization direction of the first optical signal is the second direction perpendicular to the first direction;
• a demodulating unit that causes the first optical signal guided in the first optical path or the second optical path by the guiding unit and the second optical signal branched by the branching unit to interfere with each other, thereby demodulating the optical signal;
• and
• a polarization direction adjusting unit that judges a code error rate of the optical signal demodulated by the demodulating unit to adjust the polarization direction of the first optical signal acquired by the guiding unit in the first direction or the second direction.

A delayed interferometer comprising:

• a first splitter that branches an optical signal modulated by a phase modulation system into a first optical signal and a second optical signal;
• a second splitter that acquires the first optical signal branched by the first splitter, guides the first optical signal in a first optical path to delay the first optical signal when a polarization direction of the acquired first optical signal is the first direction, and guides the first optical signal in a second optical path having an optical distance shorter than that of the first optical path when the polarization direction of the first optical signal is the second direction perpendicular to the first direction;
• a third splitter that causes the first optical signal guided in the first optical path or the second optical path by the second splitter and the second optical signal branched by the first splitter to interfere with each other, thereby demodulating the optical signal;
• and
• a liquid crystal controller that judges a code error rate of the optical signal demodulated by the third splitter to adjust the polarization direction of the first optical signal acquired by the second splitter in the first direction or the second direction.