Multi-Layer Optical Sheet for Head-Mounted Display Image Sharpness
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Solution Overview
Problem
Head-mounted display devices often suffer from non-image regions caused by non-pixel areas between pixels, which are enlarged and visible to the viewer, hindering sharp image display.
Innovation Solution
A display device incorporating an optical sheet with multiple layers and convex shapes at interfaces, where the refractive index difference between layers is 0.005-0.1 and the half-value angle is 0.05-0.2 degrees, diffusing image light to minimize the visibility of non-image regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the image light emitted from the image source is enlarged by the lens, then the image sharpness is improved, but the non-image regions caused by non-pixel regions are also enlarged and become visually recognizable
Solution Approach 1:
An optical sheet is introduced as an intermediary component between the image source and the lens. This optical sheet diffuses the image light in a controlled manner, preventing the lens from magnifying the non-image regions while still allowing the image to be displayed sharply. The optical sheet acts as a mediator that modifies the light path to eliminate the harmful effect of visible non-pixel regions.
Solution Approach 2:
The optical sheet changes the angular distribution parameter of the image light by diffusing it. Specifically, the optical sheet has a half-value angle of 0.05° or more and 0.2° or less, which controls the diffusion degree. This parameter change allows the light to fill the pupil of the viewer's eye without creating visible non-image regions, thus resolving the contradiction between image sharpness and non-image region visibility.
2Object-generated harmful factors
If an optical sheet is introduced to diffuse image light, then the non-image regions are prevented from being recognized, but the image sharpness may be reduced
Solution Approach 1:
The optical sheet's diffusion parameters are precisely controlled to maintain image sharpness. The half-value angle is set to 0.05° or more and 0.2° or less, and the diffusion angle β (where luminance is 1/20 of maximum luminance) is set to 5 times the half-value angle or less. These controlled parameter changes allow sufficient diffusion to hide non-image regions while preserving enough directional information to maintain image sharpness.
Solution Approach 2:
The optical sheet performs partial diffusion rather than complete diffusion of the image light. By controlling the diffusion angle to be within specific limits, only the minimal necessary diffusion is applied to eliminate visible non-image regions, while the majority of the light maintains its original directional information, thus preserving image sharpness.
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 solution effectively prevents the recognition of non-image regions, ensuring a sharper image by subtly diffusing image light, while protecting the lens and maintaining image clarity.
Implementation Method 1
an optical sheet (20, 220, 320) that is disposed between the image source and the lens or at the viewer side of the lens, wherein the optical sheet has at least two or more optical layers, and a plurality of unit shapes (21a, 221a, 321a, 23a, 223a, 323a) are formed at each interface between the optical layers
Implementation Method 2
in the optical sheet, a difference Δn in refractive index between adjacent layers satisfies 0.005≤Δn≤0.1, a half-value angle α of the optical sheet satisfies 0.05°≤α≤0.2°
Data Source
AI summary
A display device comprised by being provided with: an image source for emitting image light; a lens for enlarging the image light and emitting the image light to the viewer side; and an optical sheet disposed between the image source and the lens or on the viewer side of the lens, wherein the optical sheet comprises at least two or more layers, a plurality of convex shapes are formed at interfaces between the layers, a difference Δn in refractive index between the layers adjacent to each other satisfies 0.005≤Δn≤0.1, a half-value angle α of the optical sheet satisfies 0.05°≤α≤0.2°, and a diffusion angle β of the optical sheet at which a maximum brightness becomes 1/20 satisfies β≤5×α.