Patent ID: 7764851

Claim:
An optical modulator comprising: an optical waveguide substrate comprising a first principal surface and a second principal surface, a pair of side surfaces, and an incident face and exit face of light, the substrate comprising a ferroelectric material; a channel optical waveguide comprising at least a pair of branch sections, a multiplexing section of the branch sections and an exit section provided on the downstream of the multiplexing section, the waveguide being formed on the first principal surface; a modulation electrode for applying a signal voltage for modulating light propagating in the branch sections, the modulation electrode being formed on the first principal surface of the optical waveguide substrate; a support substrate; an adhesive layer adhering the second principal surface of the optical waveguide substrate to the support substrate; a photodetector mounted on the first principal surface of the optical waveguide substrate; and a reflective groove for reflecting leaked light of off-mode emitted from the multiplexing section and emitting the light from the first principal surface, the reflective groove penetrating through the optical waveguide substrate between the first principal surface and the second principal surface and extending into the adhesive layer, wherein: an operating point of the optical modulator is controlled by changing a DC bias applied on the modulation electrode based on optical output of the leaked light of off-mode.