Patent ID: 8170381

Claim:
An optical modulator, comprising: a substrate having an electro-optical effect; two pieces of optical waveguides formed in said substrate; a buffer layer formed on said substrate; a traveling-wave electrode composed of a center conductor and a ground conductor disposed above said buffer layer; and a ridge section structured with a recessed section that is formed by carving at least a part of said substrate in an area where a strength of electrical field of high-frequency electrical signal propagating through said traveling-wave electrode is strong, wherein said ridge section includes a center conductor ridge section where said center conductor is formed in an upper portion thereof and a ground conductor ridge section where said ground conductor is formed in an upper portion thereof, said center conductor ridge section is provided with one of said two pieces of optical waveguides, and said ground conductor ridge section is provided with the other one of said two pieces of optical waveguides, said recessed section includes a first, a second and a third recessed sections, said second recessed section and said third recessed section are formed at symmetrical positions with respect to a center line of said first recessed section, said center conductor ridge section is formed between said first recessed section and said second recessed section, said ground conductor ridge section is formed between said first recessed section and said third recessed section, said ground conductor is not provided above said first recessed section and said second recessed section, one portion of said ground conductor where said ground conductor is formed and another portion of said ground conductor where said ground conductor is not formed are alternately provided above said third recessed section in a direction of said optical waveguide, and one portion of said ground conductor where said ground conductor is formed and another portion of said ground conductor where said ground conductor is not formed are alternately provided above said substrate adjacent to said second recessed section on a side where said center conductor ridge section does not lie and at a position symmetrical to said third recessed section with respect to a center line of said center conductor in the direction of said optical waveguide in a similar manner to said third recessed section.