Abstract: An optical phase modulator includes a main Mach-Zehnder interferometer having first and second main optical waveguide path arms, whose initial phase difference in the used wavelength is ?, a first sub Mach-Zehnder interferometer having first and second sub optical waveguide path arms that are formed in the first main optical waveguide path arm, whose initial phase difference in the used wavelength is 0, and a second sub Mach-Zehnder interferometer having third and fourth sub optical waveguide path arms that are formed in the second main optical waveguide path arm, and whose initial phase difference in the used wavelength is 0. Of each of the main optical waveguide path arms and the sub optical waveguide path arms, at least the portions where high-frequency electrodes are formed are constructed using semiconductor waveguide paths, and reduce the effects of frequency chirping caused by an orthogonal component due to light absorption in the semiconductor.

Abstract: The optical phase modulator of the present invention comprises: a main Mach-Zehnder interferometer having first and second main optical waveguide path arms, and whose initial phase difference in the used wavelength is ?; a first sub Mach-Zehnder interferometer having first and second sub optical waveguide path arms that are formed in said first main optical waveguide path arm, and whose initial phase difference in the used wavelength is 0; and a second sub Mach-Zehnder interferometer having third and fourth sub optical waveguide path arms that are formed in said second main optical waveguide path arm, and whose initial phase difference in the used wavelength is 0.