Optical receiving apparatus and optical communication system comprising it

摘要

A phase shift unit (12) provides a prescribed phase difference (À2, for example) between a pair of optical signals transmitted via a pair of arms constituting a data modulation unit (20) . A low-frequency signal f 0 is superimposed on one of the optical signals. A signal of which phase is shifted by À/2 from the low-frequency signal f 0 is superimposed on the other optical signal. A pair of the optical signals is coupled, and a part of which is converted into an electrical signal by a photodiode (3). 2f 0 component contained in the electrical signal is extracted. Bias voltage provided to the phase shift unit (12) is controlled by feedback control so that the 2f 0 component becomes the minimum.