Patent ID: 8412005

Claim:
A Mach-Zehnder interferometer type optical modulator comprising: a first optical waveguide and a second optical waveguide; an input optical coupler optically connected to one end of each of the first and second optical waveguides; an output optical coupler optically connected to the other end of each of the first and second optical waveguides; and a phase shifting section disposed between the input optical coupler and the output optical coupler, wherein the phase shifting section constitutes part of the first optical waveguide and part of the second optical waveguide and includes a first optical waveguide structure and a second optical waveguide structure each including an n-type semiconductor section, a core layer on the n-type semiconductor section, and a cladding layer on the core layer, the cladding layer of the first optical waveguide structure includes a first section disposed on the core layer of the first optical waveguide structure, and a second section and a third section disposed on the first section, the second section and the third section being juxtaposed to each other in a direction that intersects a waveguiding direction of the first optical waveguide structure, the cladding layer of the second optical waveguide structure includes a fourth section disposed on the core layer of the second optical waveguide structure, and a fifth section and a sixth section disposed on the fourth section, the fifth section and the sixth section being juxtaposed to each other in a direction that intersects a waveguiding direction of the second optical waveguide structure, and the first section, the second section, the fourth section, and the fifth section are composed of a p-type semiconductor, and the third section and the sixth section are composed of an undoped semiconductor.