Light Guide Substrate Stray Light Suppression
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Solution Overview
Problem
Image display devices with rectilinear propagation light guides face issues with stray light generation due to image light reflection, leading to ghost images and reduced visibility of virtual images.
Innovation Solution
Incorporating a reflection suppressing portion with a transparent or light-absorbing material at the interface of the light guide substrate to minimize stray light by preventing image light reflection and absorption, ensuring that image light propagates without hitting the substrate surfaces, thereby reducing stray light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a rectilinear propagation light guide is used to guide image light, then the optical path is shortened and the system is miniaturized, but stray light is generated due to reflection at substrate surfaces causing ghost images
Solution Approach 1:
The patent applies the principle of converting harm into benefit by treating the substrate surfaces that would normally cause harmful reflections as useful components. By designing the light guide with specific surface configurations and utilizing the substrate surfaces for controlled light guidance, the harmful stray light reflections are converted into beneficial light transmission paths, eliminating ghost images while maintaining compact system size
Solution Approach 2:
The patent introduces an intermediary element (such as a coating layer or intermediate substrate) between the light guide substrate and the external environment. This intermediary layer mediates the light interaction by suppressing unwanted reflections at the substrate surfaces while maintaining the rectilinear propagation path, thereby eliminating stray light without increasing the overall optical path length
2Illumination intensity
If image light is reflected by substrate surfaces in the light guide, then light transmission is enhanced, but ghost images are formed due to stray light reaching the user's eyes
Solution Approach 1:
The patent applies local quality by treating different surfaces of the light guide differently. Specific surfaces are designed with different optical properties (e.g., reflective vs. transmissive, or different refractive indices) to achieve localized light control. This allows certain substrate surfaces to transmit light while others suppress reflections, thereby maintaining light transmission intensity while eliminating ghost images from stray light paths
Solution Approach 2:
The patent changes optical parameters such as refractive index, surface roughness, or coating properties of the substrate surfaces to control light behavior. By adjusting these parameters, the patent optimizes light transmission while suppressing the reflection that causes ghost images, achieving both high illumination intensity and clean image quality without additional optical path length
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
This solution effectively reduces stray light and ghost images, enhancing the visibility of virtual images displayed before the user's eyes by spatially separating stray light from the regular image light, resulting in improved image clarity.
Implementation Method 1
a reflection suppressing portion with a transparent or light-absorbing material at the interface of the light guide substrate to minimize stray light by preventing image light reflection and absorption
Implementation Method 2
a light guide 50 includes a transparent substrate 500... Inside the substrate 500, a single incident-side reflective surface 501 and a plurality of first to third (three in this embodiment) exit-side reflective surfaces 502a to 502c are formed
Data Source
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AI summary
In an image display device in which two light guides are combined, flat plates (16, 17) of the same material as that of a substrate (11) of a first light guide (10) is affixed to the outsides of a first surface (11a) and a second surface (11b) of the substrate (11), the fist surface (11a) and the second surface (11b) opposing each other. Image light introduced into the substrate (11) is reflected by an incident-side reflective surface (12) toward exit-side reflective surface (13a to 13f), which are half mirrors, and a part of the image light is reflected in stages by the respective exit-side reflective surfaces (13a and 13f) and the remainder of the image light is transmitted. The image light reflected by the exit-side reflective surfaces (13a to 13f) is emitted through the second flat plate (17) and introduced into a second light guide. The part of the image light reflected by the incident-side reflective surface (12) reaches the interface between the first surface (11a) and the first flat plate (16), but enters the flat plate (16) without being reflected, and hits and is absorbed by a light-absorbing sheet (18). This reduces the occurrence of stray light and improves the visibility of a virtual image displayed before user's eyes.