Optical waveguide element

An optical waveguide element in which an optical waveguide is formed on a substrate,

• the optical waveguide has a main waveguide that propagates signal light, a waveguide for unnecessary light that guides unnecessary light released from the main waveguide, and a waveguide for collecting unnecessary light to which the unnecessary light emitted from the waveguide for unnecessary light is introduced,
• wherein the waveguide for unnecessary light is connected to the waveguide for collecting unnecessary light via a waveguide for connection, and
• a width of the waveguide for connection, which is a width in a direction that perpendicularly intersects a propagation direction of the unnecessary light, at a portion connected to the waveguide for collecting unnecessary light is set to be wider than a width at a portion connected to the waveguide for unnecessary light with the waveguide for connection,
• wherein a distance from a connection point between a boundary of the waveguide for connection on a side that is closer to the waveguide for collecting unnecessary light and the waveguide for collecting unnecessary light to a center line of the waveguide for connection is longer than a distance from a connection point between a boundary of a shape formed with an extension of the waveguide for unnecessary light on a side that is closer to the waveguide for collecting unnecessary light and the waveguide for collecting unnecessary light to the center line of the waveguide for connection in a plan view of the substrate.