Head-Mounted Display Light Guide Plates Wavelength-Selective Reflectance
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Solution Overview
Problem
Existing head-mounted displays (HMDs) face challenges in achieving a wider angle of view while minimizing thickness, size, and weight, leading to color unevenness due to increased light absorption by high refractive index light guide plates, particularly on the blue wavelength side.
Innovation Solution
The HMD employs a first and second light guide plate with parallel main surfaces for internal reflection, where the reflectance of the blue wavelength region in the emission/reflection plane farthest from the incident plane is higher than in the green and red wavelength regions, optimizing reflectance characteristics to mitigate color unevenness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the refractive index of the light guide plate material is increased to achieve a wider angle of view and reduced thickness, then the angle of view and compactness are improved, but light absorption increases particularly on the blue wavelength side causing color unevenness
Solution Approach 1:
The patent applies local quality by making the reflectance characteristic of the emission/reflection plane wavelength-dependent. Specifically, the blue wavelength region has higher reflectance than the green and red wavelength regions in the emission plane farthest from the incident plane. This localized adjustment of reflectance properties at different wavelengths compensates for the increased blue light absorption in high refractive index materials, thereby resolving the color unevenness while maintaining the wide angle of view capability
2Length of stationary object
If the refractive index of the light guide plate material is increased to reduce thickness and size, then the device becomes more compact, but light absorption increases causing deterioration of blue wavelength emission efficiency
Solution Approach 1:
The patent applies parameter changes by adjusting the reflectance parameter of the emission/reflection plane in a wavelength-selective manner. By setting the blue wavelength reflectance higher than green and red wavelengths in the emission plane farthest from the incident plane, the system compensates for the increased absorption losses in high refractive index, thin light guide plates. This parameter adjustment restores blue wavelength emission efficiency while maintaining the reduced thickness and compact size
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 configuration enables the HMD to display images with a wider angle of view without color unevenness, while reducing thickness, size, and weight, thereby improving image quality and user experience.
Implementation Method 1
since the light guide plate causes image light to propagate to user's eyes by using optical confinement due to total internal reflection
Implementation Method 2
A reflectance of blue wavelength region in an emission/reflection plane farthest from the incident plane of the first light guide plate is higher than a reflectance in a green wavelength region and a red wavelength region
Data Source
AI summary
The head-mounted display includes: an image display unit that generates an image to be displayed; and a first light guide plate and a second light guide plate which duplicate image light from the image display unit. Each of the first light guide plate and the second light guide plate includes a set of parallel main surfaces confining the image light with internal reflection, the first light guide plate includes an incident plane that reflects the image light to an inner side, and two or more emission/reflection planes from which the image light is emitted to the second light guide plate, the second light guide plate includes an input part that couples the image light transmitted from the first light guide plate to the inner side, and an output part from which the image light is emitted to a user's pupil.