Patent ID: 8705987

Claim:
A signal processing circuit, comprising: an optical frequency deviation estimating unit that inputs a plurality of signal data that are generated by mixing a plurality of optical carrier waves with a local light, which optical carrier waves are phase-modulated and have polarizations able to be demultiplexed from each other, and that corresponds to the polarizations of each of the optical carrier waves, that estimates a frequency deviation which is included in each of the plurality of input signal data and is a difference between a frequency of the optical carrier wave and a frequency of the local light, per the signal data, and that outputs the estimated frequency deviation as an estimated value; an optical frequency deviation compensation amount analyzing unit that calculates an amount of frequency compensation which is an amount of compensation to make a phase of the signal data rotated so as to reduce the frequency deviation, on the basis of a plurality of the estimated values estimated per the signal data; an optical frequency deviation compensating unit that makes the phase of the signal data rotated correspondingly to the amount of the frequency compensation; an optical phase deviation estimating unit that estimates a phase deviation included in each the input signal data and is a difference between a phase of the optical carrier wave and a phase of the local light, per the signal data; and an optical phase deviation compensating unit that makes the phase of the signal data rotated correspondingly to the phase deviation.