Optical modulator, method of achieving velocity matching and impedance matching of optical modulator, and method of manufacturing optical modulator

摘要

A Mach-Zehnder optical waveguide (12) is disposed in a substrate (11) made of a material having an electro-optic effect. Coplanar-waveguide (CPW) modulating electrodes (13, 14) are disposed on a principal surface (11A) of the substrate (11). A dielectric layer (16) is disposed on a reverse surface (11B) of the substrate (11). A supporting substrate (17) having a recess (18) is disposed in contact with the dielectric layer (16) such that the recess (18) is located at a position corresponding to a modulating region (P). The relationship: ε_r ε_s is satisfied where ε_r represents the dielectric constant of the supporting substrate (17) and ε_s represents the dielectric constant of the dielectric constant of solid, liquid, or gaseous substance in the recess (18).