Abstract: In the present invention, for example with regards to a Mach-Zehnder type LN modulator which uses a Z-cut LN substrate, by providing a step by forming an etching part on the surface of the LN substrate, and forming an optical waveguide so as to position a pair of branching waveguides of a Mach-Zehnder interferometer in the step portion, a height difference is produced between the branching waveguides, in the perpendicular direction to the substrate surface. As a result, lines of electric force directed from a signal electrode provided above one branching waveguide towards a ground electrode provided above an other branching waveguide are hardly dispersed, and a desired electro-optic effect can be obtained at a lower drive voltage.

Abstract: The present invention has an object to provide an optical device capable of leading out a light propagated through an optical waveguide to a desired substrate side face while maintaining the sufficient power of the light, within a range of limited substrate size. To this end, according to the optical device of the present invention, a groove is formed in the vicinity of an end portion on the optical output side of the optical waveguide, on the substrate on which the optical waveguide is formed, a side wall of the groove is used as a reflecting plane, the light output from the optical waveguide is reflected by the reflecting plane, and the reflected light is emitted from the desired substrate side face.