Patent ID: 7912325

Claim:
An optical control element comprising: a substrate formed of a material having an electro-optical effect; and an optical waveguide with at least one Mach-Zehnder type optical waveguide having an input-side optical waveguide portion, two branched optical waveguide portions and an output-side optical waveguide portion formed on a top or a bottom surface of the substrate, wherein propagation constants in a non-modulation region of the input-side optical waveguide portion and the output-side optical waveguide portion are set to be different from a propagation constant in a modulation region of the branched optical waveguide portions, the modulation region of the branched optical waveguide portion is divided into three or more regions, in the respective three or more regions, propagation constants are set such that the propagation constants are not equal to each other in the two branched optical waveguide portions, and a total sum of effective propagation constants obtained by multiplying each propagation constant by a length of each of the respective three or more regions are set to be equal in the respective branched optical waveguide portions.