Patent ID: 7088875

Claim:
An optical modulator of Mach-Zehnder type in which an optical waveguide with a structure of a Mach-Zehnder interferometer is formed on a substrate having an electro-optical effect, a signal electrode and a ground electrode are disposed along a pair of waveguides positioned between a branching section and a multiplexing section of said optical waveguide, and lights being propagated through said optical waveguide are modulated by applying an electrical signal to said signal electrode, said substrate including: a polarization inversed region, which is formed by inversing a direction of polarization of a part of a region relative to a direction of polarization of another part of the region, in an interaction portion where the lights being propagated through said pair of waveguides and the electrical signal being propagated through said signal electrode interact; and ridge structure sections formed by lowering areas of the substrate on both sides of each of said pair of waveguides along the waveguides, and said signal electrode being arranged in the vicinity of one of said pair of waveguides in the polarization inversed region of said interaction portion, and is arranged in the vicinity of the other waveguide in a non-inversed region of the interaction portion where the polarity is not inversed.