Patent ID: 7551820

Claim:
An optical device, comprising: a substrate having an electro-optic effect; an optical waveguide formed on a surface layer portion of said substrate and including a modulating optical waveguide for performing optical modulation for light inputted to said substrate and an output optical waveguide and a monitoring optical waveguide branched from and connected to a downstream side portion of said modulating optical waveguide, said monitoring optical waveguide guiding light for monitoring optical modulation operation of said modulating optical waveguide; and a reflecting groove provided on the downstream side of said monitoring optical waveguide, the reflecting groove including a first portion that reflects light propagated along said monitoring optical waveguide to a target, the width of a reflection face of said first portion being substantially equal to the cut-out width of said monitoring optical waveguide, and two second portions that are disposed on both sides of said first portion with respect to a light guiding direction of said monitoring optical waveguide, each of the second portions reflecting light propagated along said monitoring optical waveguide in a direction that results in light reflected by one of the two second portions being diverted from the target.