Patent ID: 8406577

Claim:
An optical modulator comprising: a substrate that is formed of a material having an electro-optic effect; an optical waveguide formed on the substrate, the optical waveguide having at least an input waveguide leading optical waves input to the optical modulator, branch waveguides branching from the input waveguide, and an output waveguide coupling the branch waveguides and leading the optical waves to an outside of the optical modulator; modulation electrodes formed on the substrate to modulate optical waves propagating on the optical waveguide; modulation means provided at a position on the respective branch waveguides to modulate the optical waves propagating on the branch waveguides, located at a position where at least a part of the modulation electrodes are provided; polarization plane selection means provided at a position that is located between an input optical fiber and a point where the branch waveguides are coupled, wherein said polarization plane selection means controls polarization planes of the optical waves modulated by the modulation means; and polarization plane adjustment means provided at a position that is located between the polarization plane selection means and the point where the branch waveguides are coupled, wherein said polarization plane adjustment means adjusts polarization planes such that the polarization plane of a first one of the optical waves propagating on the branch waveguides is made orthogonal to the polarization plane of a second one of the optical waves.