AR Light Guide Laminate Without Air Gap for Leak-Free Thin Optics
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Solution Overview
Problem
AR devices with an air layer between the light guide plate and optical plate are prone to damage from external forces, thickening, and light leakage, and exhibit color unevenness due to interference between reflected lights.
Innovation Solution
An AR device with a laminate comprising a light guide plate and a low refractive index layer, where the refractive index is 1.25 or less and thickness is 1.5 µm to 10 µm, without an air layer, to achieve thinning, suppress light leakage, and reduce color unevenness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an air layer is provided between the light guide plate and optical plate, then damage to the light guide plate is prevented, but the lens portion is thickened
Solution Approach 1:
A low refractive index layer is introduced as an intermediary between the light guide plate and optical plate. This layer has a refractive index lower than both the light guide plate and optical plate, creating optimal refractive index gradients that enable total internal reflection while maintaining a thin structure. The intermediary layer prevents direct contact between the light guide plate and optical plate, avoiding damage while keeping the overall thickness minimal.
Solution Approach 2:
The refractive index parameter is strategically manipulated by selecting materials with specific refractive indices. The low refractive index layer has a refractive index lower than both adjacent layers, creating the necessary conditions for total internal reflection at both interfaces. This parameter optimization allows the system to achieve protective functionality without requiring a thick air layer.
2Strength
If an air layer is provided between the light guide plate and optical plate, then damage to the light guide plate is prevented, but light leakage occurs when water or stain is attached
Solution Approach 1:
The low refractive index layer serves as a hydrophobic intermediary that prevents water or stains from directly contacting the light guide plate. This mediator layer maintains the optical interface integrity even when exposed to liquids, preventing light leakage while continuing to provide mechanical protection.
Solution Approach 2:
The low refractive index layer exhibits hydrophobic properties that repel water and liquid stains. This hydraulic repulsion effect prevents liquids from penetrating to the light guide plate surface, maintaining total internal reflection conditions even in wet environments and preventing light leakage.
3Length of stationary object
If a laminate with light guide plate and low refractive index layer is used without air layer, then thinning is achieved, but color unevenness occurs due to interference between reflected lights
Solution Approach 1:
The low refractive index layer is positioned at the specific local interface between the light guide plate and optical plate, precisely where total internal reflection occurs. This localized placement optimizes the refractive index gradient at the critical reflection interfaces without requiring a thick layer, thereby preventing color unevenness while achieving thinning.
Solution Approach 2:
The thickness of the low refractive index layer is optimized to a specific parameter range that prevents interference-induced color unevenness. By controlling the layer thickness to be within an optimal range, the optical path difference is minimized, eliminating interference effects while maintaining the thinning benefit.
4Length of stationary object
If a laminate with light guide plate and low refractive index layer is used without air layer, then thinning is achieved, but transparency is poor
Solution Approach 1:
The refractive index of the low refractive index layer is optimized to create optimal refractive index gradients at both interfaces. This parameter optimization minimizes reflection losses and maximizes light transmission through the laminate, achieving excellent transparency while maintaining the thin structure.
Solution Approach 2:
The laminate is constructed as a composite structure with three layers having different refractive indices. This composite design allows each layer to contribute specific optical properties, with the low refractive index layer enabling total internal reflection while the overall structure maintains high transparency through optimized material selection and interface design.
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 laminate achieves thinning, prevents light leakage, and maintains excellent transparency by suppressing color unevenness on the surface.
Implementation Method 1
the reflected light at the light guide plate and the reflected light at the layer having the low refractive index interfere with each other, color unevenness occurs on the surface of the laminate
Implementation Method 2
light emitted from the image generation device enters a light guide plate provided in the lens portion, and total reflection is repeated at the light guide plate to be emitted toward pupils of a user
Data Source
Figure 1
Figure 2
Figure 3A~3D
AI summary
An AR device of the present invention includes a laminate (1), and the laminate (1) has a light guide plate (2) and a low refractive index layer (3) disposed on at least one side in a thickness direction of the light guide plate (2). Further, a refractive index of the low refractive index layer (3) is 1.25 or less, and a thickness of the low refractive index layer (3) is 1.5 µm or more and 10 µm or less.