Optical waveguide element

An optical waveguide element comprising:

• a cladding portion made of silica-based glass;
• and
• a plurality of optical waveguides positioned in the cladding portion and made of silica-based glass in which ZrO2 crystal particles are dispersed, wherein
• the optical waveguide element is a planar lightwave circuit, and
• the plurality of optical waveguides configure a coherent mixer,
• wherein the ZrO2 crystal particles dispersed in the silica-based glass of the plurality of optical waveguides are dispersed to be separated by a distance equal to or smaller than a wavelength of a light input to the waveguide.