Abstract: An optical transmitter to drive the EA modulator integrated with an LD in a mode of lowered power consumption. The optical transmitter includes the optical device integrating the LD with the EA modulator, and the driver to modulate the EA modulator in the differential mode by being supplied with the modulation signal between the anode and the cathode common to the LD.

Abstract: An optical receiver includes a light-receiving part and a control part. The light-receiving part includes an APD, a PIN-PD, and a branching optical device. First signal light is incident on the light-receiving part and is divided into second signal light and third signal light which are incident on the APD and the PIN-PD, respectively, by the branching optical device. Due to this structure, the third signal light is incident on the PIN-PD without the quantity thereof being varied depending on the polarization state of the first signal light. The control part generates a supply voltage at which a desired avalanche multiplication factor is obtained in the APD on the basis of the output current from the PIN-PD. According to the above-described structure, the avalanche multiplication factor of the APD is accurately controlled on the basis of the output current of the PIN-PD.

Abstract: An optical multiplexer/demultiplexer is provided with a first member, a second member and an optical filter. The first member is a planar waveguide and is formed with an optical waveguide and another optical waveguide. The second member is a planar waveguide and is formed with an optical waveguide and another optical waveguide. The optical filter is a dielectric multi-layered filter and is sandwiched between the end face of the first member and the end face of the second member.