Optical waveguide element

An optical waveguide element connected between a first waveguide portion and a second waveguide portion each formed on a substrate, comprising:

• a polarization rotation portion including a first tapered portion that is formed in a first layer located above the substrate and that is connected to the first waveguide portion, and
• a first reverse-tapered portion that is formed in a second layer located above the substrate and that is connected to the second waveguide portion, the second layer being different from the first layer,
• wherein the first tapered portion includes a material different from a material of the first reverse-tapered portion,
• in a plan view of the substrate, the first tapered portion has a part that is overlapping with a part of the first reverse-tapered portion,
• the first waveguide portion, the polarization rotation portion, and the second waveguide portion are arranged in order along a first direction,
• the first tapered portion has a length in a second direction that changes along the first direction, the second direction intersecting the first direction,
• the first reverse-tapered portion has a length in the second direction that changes along the first direction, and
• in a plan view of the substrate, the optical waveguide element has a distance in the second direction between a first center line and a second center line that changes along the first direction, the first center line extending along a center of the first tapered portion in the second direction, the second center line extending along a center of the first reverse-tapered portion in the second direction.