US Patent 7302193 Optical receiver

An optical receiver includes a PIN photodiode (PIN-PD) having an incident surface for receiving signal light, the PIN-PD transmitting a part of the signal light to the surface opposite to the incident surface, and an avalanche photodiode (APD) having an incident surface for receiving light transmitted through the PIN-PD. In the optical receiver, the ratio of the quantity of signal light detected by the PIN-PD and the ratio of the quantity of signal light detected by the APD are not affected by the polarization state of the signal light incident on the optical receiver, and accordingly the avalanche multiplication factor of the APD is suitably controlled on the basis of the signal light detected by the PIN-PD.