Optical waveguide element, optical modulation device using optical waveguide element, and optical transmission device using optical waveguide element

Abstract

Provided is an optical waveguide element including spot size conversion means with suppressed optical insertion loss without complicating a manufacturing process. An optical waveguide element includes an optical waveguide substrate () having a rib-type optical waveguide () formed of a material having an electro-optic effect, and spot size conversion means for changing a mode field diameter of a light wave propagating through the optical waveguide at a position where an input end or an output end of the rib-type optical waveguide () is formed, in which the spot size conversion means includes a first configuration layer () that is connected to the rib-type optical waveguide () and includes a tapered portion () in which a width of the optical waveguide expands, a second configuration layer () that is laminated on the first configuration layer () and has a width narrower than a width of the first configuration layer (), and a third configuration layer () that is disposed to cover the second configuration layer () excluding a part of the second configuration layer () close to the rib-type optical waveguide and has a width wider than the width of the second configuration layer ().