Patent ID: 7689067

Claim:
A nested modulator, comprising: a substrate made of a material having electro-optic effects; an optical waveguide formed on the substrate; and a modulating electrode for modulating light waves which are guided through the optical waveguide, said optical waveguide comprising a main Mach-Zehnder waveguide, and a plurality of sub-Mach-Zehnder waveguides provided on two branching waveguides of the main Mach-Zehnder waveguide, said each sub-Mach-Zehnder waveguide comprising two sub-branching waveguides, and said modulating electrode being provided in a sub-branching waveguide of the sub-Mach-Zehnder waveguides, wherein a polarization reversal region is formed in a portion of one of said two sub-branching waveguides on a same side of each of the plurality of sub-Mach-Zehnder waveguides, the modulating electrode is formed of signal electrodes including introduced signal electrodes, branching signal electrodes and lead signal electrodes, as well as ground electrodes for each of sub-Mach-Zehnder waveguides, and the branching signal electrodes that branch from the introduced signal electrode are positioned so that said branching signal electrodes that branch from the introduced signal electrode work on said two sub-branching waveguides for each of the sub-Mach-Zehnder waveguides.