Patent ID: 8396336

Claim:
A 4-value optical phase modulator comprising: a first binary optical phase modulator and a second binary optical phase modulator, each comprising: a main Mach-Zehnder interferometer having a first main optical waveguide path arm and a second main optical waveguide path arm, which have a first high-frequency electrode and a second high-frequency electrode, respectively, and whose initial phase difference in the used wavelength is π; a first sub Mach-Zehnder interferometer having a first sub optical waveguide path arm and a second sub optical waveguide path arm that are formed in said first main optical waveguide path arm, which have a third high-frequency electrode and a fourth high-frequency electrode, respectively, and whose initial phase difference in the used wavelength is 0; and a second sub Mach-Zehnder interferometer having a third sub optical waveguide path arm and a fourth sub optical waveguide path arm that are formed in said second main optical waveguide path arm, which have a fifth high-frequency electrode and a sixth high-frequency electrode, respectively, and whose initial phase difference in the used wavelength is 0; wherein of said first and second main optical waveguide path arms and said first through fourth sub optical waveguide path arms, at least the portion where said first through sixth high-frequency electrodes are formed are semiconductor waveguide paths that are formed on a semiconductor substrate; an input optical waveguide path that divides an input light at input ends of said first binary optical phase modulator and said second binary optical phase modulator; an output optical waveguide path that combines the light from output ends of said first binary optical phase modulator and said second binary optical phase modulator; and phase shifters that cause a phase of output light from said first binary optical phase modulator and said second binary optical phase modulator to differ by π/2.