OPTICAL 90-DEGREE HYBRID CIRCUIT AND OPTICAL RECEIVER USING SAME

摘要

An object of the present invention is to provide an optical 90-degree hybrid circuit which is capable of easily adjusting the optical power ratio between signal and local oscillator and suppresses an optical system of an optical receiver becoming complex and optical receivers using the same. The optical 90-degree hybrid circuit for demodulating multilevel phase-modulated signals corresponding to individual polarized waves by multiplexing an optical wave having a predetermined plane of polarization contained in signal and local oscillator that has the same wavelength as the signal and has been adjusted to circularly-polarized signal, and polarization-splitting the multiplexed signal includes polarization splitting means (polarization splitting) for extracting an optical wave having a predetermined plane of polarization from the signal, a polarization conversion element for rotating a plane of polarization of the optical wave extracted from the polarization splitting means, and a polarizer that determines a plane of polarization of the signal before multiplexing the signal with the local oscillator, and the polarization splitting means, the polarization conversion element, and the polarizer adjust intensity of the optical signal (VOA function) in cooperation with each other.