Patent ID: 8103177

Claim:
A frequency offset detecting apparatus, used in a digital coherent optical receiver, the digital coherent optical receiver comprising: a front-end processing section, for generating a digital baseband electric signal; and an equalizer, for performing equalized filtering on the digital baseband electric signal; the frequency offset detecting apparatus, for detecting frequency offset contained in the digital baseband electric signal or in a signal outputted by the equalizer; wherein the frequency offset detecting apparatus comprises an argument difference obtaining unit, a first subtracter ( 306 ), a second subtracter ( 310 ), a quantizer ( 308 ) and an averager ( 312 ), of which the argument difference obtaining unit obtains an argument difference of adjacent symbols in a signal inputted therein; the first subtracter ( 306 ) subtracts an output of the averager from the argument difference obtained by the argument difference obtaining unit; the quantizer ( 308 ) performs uniform quantization with predetermined intervals on an output of the first subtracter; the second subtracter ( 310 ) subtracts an output of the quantizer ( 308 ) from the argument difference obtained by the argument difference obtaining unit; and the averager averages an output of the second subtracter ( 310 ).