Glass Sheet End Surface Roughness for Stray Light Suppression
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Solution Overview
Problem
In wearable image display devices, stray light generated from light-guiding plates disrupts digital images, and existing materials like acrylic resin are inadequate due to high minimum incident angles and low rigidity, making it difficult to achieve high-definition nanoimprint.
Innovation Solution
A glass sheet with a refractive index of 1.6 to 2.2, an R-shaped end surface, and surface roughness of 100 nm or less is used, allowing efficient emission of light and reducing scattering, while maintaining clarity and brightness of images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If acrylic resin is used as light-guiding plate material, then ease of manufacture is improved, but manufacturing precision deteriorates due to low rigidity making high-definition nanoimprint difficult
Solution Approach 1:
The patent changes the material parameter from acrylic resin to glass, fundamentally altering the rigidity and refractive index characteristics. This enables the application of high-definition nanoimprint technology while maintaining manufacturability through established glass processing techniques.
Solution Approach 2:
The patent specifies a glass composition containing SiO2 (30-70 mass%), B2O3 (5-20 mass%), and Al2O3 (5-20 mass%), creating a composite glass material that optimizes both rigidity for nanoimprint and refractive index for light guidance functionality.
2Ease of manufacture
If acrylic resin is used as light-guiding plate material, then ease of manufacture is improved, but reliability deteriorates due to large minimum incident angle causing poor light propagation
Solution Approach 1:
The patent changes the refractive index parameter by switching from acrylic resin to glass, which has a larger refractive index difference. This reduces the minimum incident angle for total reflection, improving light propagation reliability while maintaining manufacturing feasibility.
3Illumination intensity
If end surface is made flat for light guidance, then light propagation is improved, but stray light generation increases due to total reflection at end surface
Solution Approach 1:
The patent applies different surface qualities to different regions: the principal surfaces maintain high flatness for light guidance, while the end surface is intentionally made rough with Ra ≥ 1.0 μm to scatter and absorb stray light, converting a harmful effect into a beneficial one.
Solution Approach 2:
The patent converts the harmful total reflection at the end surface into a beneficial effect by making the end surface rough. The roughness causes light scattering and absorption, transforming the stray light problem into a stray light suppression solution.
4Reliability
If glass with high refractive index is used, then light guidance reliability is improved, but weight increases causing device discomfort
Solution Approach 1:
The patent optimizes the glass composition to achieve a balanced refractive index (1.50 ≤ nd < 1.70) that provides sufficient light guidance reliability while controlling density to minimize weight, creating an optimal compromise between optical performance and wearable comfort.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The glass sheet effectively suppresses stray light, enhancing image clarity and reducing device weight, thus minimizing discomfort during use in wearable image display devices.
Implementation Method 1
of the light having entered the inside of the glass sheet, the light having reached the end surface of the glass sheet is totally reflected by the end surface of the glass sheet
Implementation Method 2
the scattering of the light having reached the end surface of the glass sheet on the end surface is suppressed
Data Source
AI summary
Provided is a glass sheet capable of suppressing the generation of stray light when used as a light-guiding plate of an eyeglass-type device such as a head-mounted display. The glass sheet is a glass sheet (1) including a first principal surface (1a) and a second principal surface (1b) opposed to each other and an end surface (1c) connecting the first principal surface (1a) and the second principal surface (1b) to each other, wherein the glass sheet (1) has a refractive index (nd) of from 1.6 to 2.2 and has an R shape in at least part of the end surface (1c), and the end surface (1c) has a surface roughness Ra of 100 nm or less.