Patent ID: 8867911

Claim:
A device to detect a phase difference between an I-component and a Q-component of an optical signal caused by an optical hybrid by coupling signal light with local light, the device comprising: a detector to detect a positive element and a negative element of each of the I-component and the Q-component; a compensator to generate a compensated I-component so as to keep an equivalent magnitude of the I-component in constant and generate a compensated Q-component so as to keep an equivalent magnitude of the Q-component in constant; and an evaluator to determine a phase difference between the compensated I-component and the compensated Q-component, wherein the compensator generates the compensated I-component by dividing the positive element and the negative element of the I-component by a sum of the positive element and the negative element of the I-component, and the compensated Q-component by dividing the positive element and the negative element of the Q-component by a sum of the positive element and the negative element of the Q-component.