OPTICAL MODULATOR

PROBLEM TO BE SOLVED: To provide an optical modulator having improved characteristics of both DC drift and temperature drift.SOLUTION: The optical modulator includes a substrate, an optical waveguide formed on a surface of the substrate, a buffer layer formed above the optical waveguide, and an electrode that is formed above the buffer layer and is formed of a central conductor for applying voltage and a ground conductor. The substrate is formed of a polarization non-inversion region and a polarization inversion region. A conductive film for making uniform the charge generated by a pyroelectric effect in the polarization inversion region is formed at a position that is on the top surface of the substrate in the polarization inversion region and is other than an under part of the central conductor and an under part of a gap between the central conductor and the ground conductor. Thus, the temperature drift is reduced while the DC drift is suppressed.