Patent ID: 8036541
Filing Date: 2011-10-11
Classification: H04B,H04L

Abstract:
1. A coherent optical receiver comprising: a 90-degree optical hybrid circuit which receives an optical-coherent-modulated signal light and local oscillation light, splits the received signal light to quadrature components I and Q, and outputs the quadrature components I and Q; I-channel and Q-channel photo detectors which respectively receive the quadrature components I and Q output from the 90-degree optical hybrid circuit; a clock extraction circuit which demodulates the received signal light so as to reproduce a clock whose speed is the same as that of the demodulated signal and which is synchronized therewith; I-channel and Q-channel sampling circuits which sample respective signals output from the I-channel and Q-channel photo detectors, at timings determined by the reproduced clock; and a digital signal processing section which digitally processes the sampled signals fed from the I-channel and Q-channel sampling circuits to output a digital signal converted from the sampled signals, wherein a phase offset signal detected by the digital signal processing section is fed back to the clock extraction circuit so as to control the phase of the clock; and by use of filter functions realized by digital processing, the digital signal processing section compensates dispersion of light within a fiber or phase fluctuation during free-space propagation.