Patent ID: 7058241

Claim:
An optical modulator of Mach-Zehnder type comprising: an optical waveguide of a Mach-Zehnder interferometer structure disposed on a substrate having an electro-optic effect; and a signal electrode and an earth electrode disposed along a pair of parallel waveguides positioned between a branching section and a multiplexing section of said optical waveguide, for applying an electric signal on said signal electrode to modulate a light being propagated through said optical waveguide, wherein said substrate includes, in an interaction portion where lights being propagated through said pair of parallel waveguides and the electric signal being propagated through said signal electrode interact with each other, a polarization inversion region which is a part of said interaction portion and whose polarization direction is inverted with respect to a polarization direction of the remaining part of said interaction portion, said signal electrode is arranged in the vicinity of one of said pair of parallel waveguides in the polarization inversion region of said interaction portion and is arranged in the vicinity of the other parallel waveguide in a non-inversion region, whose polarization direction is not inverted, of said interaction portion, and said polarization inversion region is located such that the center of said polarization inversion region approximately coincides with the center position of the interaction portion in the propagation direction of the lights.