Waveguide device

A waveguide device, comprising:

• a waveguide formed of an optical functional material;
• a low refractive index layer in which the waveguide is buried, the low refractive index layer being formed of a low refractive index material having a refractive index smaller than a refractive index of the optical functional material;
• and
• a support substrate configured to support the low refractive index layer,
• wherein the low refractive index layer includes a first cladding part positioned on a side opposite to the support substrate across the waveguide in a thickness direction of the low refractive index layer,
• wherein the waveguide includes a first end portion and a second end portion positioned on a side opposite to the first end portion, in the thickness direction of the low refractive index layer,
• wherein, in a width direction orthogonal to the thickness direction of the low refractive index layer and a direction in which the waveguide extends, a dimension of the first end portion is equal to or smaller than a dimension of the second end portion, and is from 0.60 to 1.00 with respect to the dimension of the second end portion,
• wherein the dimension of the first end portion in the width direction of the waveguide is from 0.80 to 1.30 with respect to a dimension of the waveguide in the thickness direction of the low refractive index layer, and
• wherein, in the thickness direction of the low refractive index layer, a dimension of the first cladding part is 0.30 or more with respect to the dimension of the waveguide.