GLASS SUBSTRATE FOR LIGHT GUIDE AND VIDEO DISPLAY DEVICE

• Main Authors: TOUGE YUKIHIRO, MIYASAKA KOJI, TAKAYAMA KIMISUKE
• Format: Patent
• Language: English; Japanese
• Published: 18.10.2018
• Subjects: OPTICAL ELEMENTS, SYSTEMS, OR APPARATUS; OPTICS; PHYSICS

PROBLEM TO BE SOLVED: To suppress quality degradation due to temperature changes by a simple configuration.SOLUTION: A light guide element 13 comprises a substrate 14 for light guide and diffraction units 15, 16 formed on the surface of the substrate 14 for light guide. The distance between the substrate 14 for light guide and the surface of optical layers of the diffraction units 15, 16 is 10% or less of the thickness of the substrate 14 for light guide. The light guide element 13 is constituted so that when it is assumed that θ represents an angle formed by a beam diffracted by the diffraction units 15, 16 and propagating inside the substrate 14 for light guide and the normal direction to the substrate for light guide, D[mm] represents the distance in a direction horizontal to the substrate 14 for light guide between the center of the diffraction units 15, 16 and a position predetermined as an emission position of a beam from the substrate 14 for light guide, n represents a diffraction index of the substrate 14 for light guide in a used wavelength, α represents a linear expansion coefficient of the substrate 14 for light guide, β represents a temperature coefficient of the substrate 14 for light guide, ΔT represents a temperature change, and ΔD represents a change amount of D due to ΔT, then ΔD|=|DΔT/cosθ×(α+β/n)|≤0.15 mm is satisfied.SELECTED DRAWING: Figure 1 【課題】簡易な構成で温度変化による品質劣化を抑制する。【解決手段】導光素子１３は、導光用基板１４と、導光用基板１４の面上に形成される回折部１５，１６とを備え、導光用基板１４と回折部１５，１６の光学層の表面との間の距離が、導光用基板１４の厚みに対して１０％以下であり、回折部１５，１６によって回折され、導光用基板１４内を伝搬する光線の導光用基板の法線方向とのなす角度をθ、回折部１５，１６の中心と光線の導光用基板１４からの出射位置として予め定められている位置との間の導光用基板１４に水平な方向での距離をＤ［ｍｍ］、導光用基板１４の使用波長における屈折率をｎ、導光用基板１４の線膨張係数をα、導光用基板１４の屈折率の温度係数をβ，温度変化をΔＴ，ΔＴによるＤの変化量をΔＤとしたときΔＤ｜＝｜ＤΔＴ／ｃｏｓ２θ×（α＋β／ｎ）｜≦０．１５ｍｍを満たすよう構成されている。【選択図】図１