Optical waveguide element and manufacturing method therefor

An optical waveguide element, comprising:

• an optical waveguide which is formed on one surface of a substrate;
• an incidence part for light to be incident into the optical waveguide or an emission part for emitting light from the optical waveguide which is disposed in an end portion of the substrate;
• and
• a dielectric film which is formed on the optical waveguide of at least one of the incidence part and the emission part, and the vicinity thereof,
• wherein in the dielectric film, dielectric films including a dielectric film formed of a first material having an index of refraction higher than an index of refraction of the substrate and a dielectric film formed of a second material having an index of refraction lower than the index of refraction of the substrate are alternately laminated,
• wherein the substrate is lithium niobate, and the dielectric film is constituted of an oxide film or a nitride film containing at least one or more elements of niobium, tantalum, silicon, titanium, zirconia, yttria, tellurium, hafnium, zinc, aluminum, magnesium, and germanium, and
• a coefficient of linear expansion of at least one material of the first material or the second material of the dielectric film is a value between coefficients of linear expansion of an axis a and an axis c of lithium niobate.