LIGHT GUIDE ELEMENT AND IMAGE DISPLAY DEVICE

摘要

A light guide element includes a light-guiding substrate and a diffraction part formed on a surface of the light-guiding substrate. The diffraction part includes an optical layer capable of exerting a diffractive action. The distance from the light-guiding substrate to a surface of the optical layer is equal to or less than 10% of a thickness of the light-guiding substrate. The light guide element satisfies |ΔD|≦0.15 mm, where ΔD is an amount of a change in D with the temperature change ΔT, D [mm] is a distance, at the temperature T (° C.), between the center of the diffraction part and a position predetermined as a position where the ray of light comes out of the light-guiding substrate in a direction horizontal with respect to the light-guiding substrate, and ΔT is a temperature change.

主权项

1. A light guide element comprising a light-guiding substrate and a diffraction part formed on a surface of the light-guiding substrate, wherein
the diffraction part includes an optical layer capable of exerting a diffractive action, a distance from the light-guiding substrate to a surface of the optical layer is equal to or less than 10% of a thickness of the light-guiding substrate, and the light guide element satisfies
|ΔD|=|DΔT/cos2 θ×(α+β/n)|≦0.15 mmwherein θ is an angle formed by a direction normal to the light-guiding substrate and a ray of light that is diffracted by the diffraction part and is propagated in the light-guiding substrate, T (° C.) is a temperature, D [mm] is a distance, at the temperature T, between the center of the diffraction part and a position predetermined as a position where the ray of light comes out of the light-guiding substrate in a direction horizontal with respect to the light-guiding substrate, n is a refractive index of the light-guiding substrate at a wavelength used, α [1/° C.] is a coefficient of linear expansion of the light-guiding substrate, β [1/° C.] is a temperature coefficient of the refractive index of the light-guiding substrate, ΔT is a temperature change, and ΔD is an amount of a change in D with the temperature change ΔT.