Optical Element with Inclined Mirrors for Head-Mounted Displays
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Solution Overview
Problem
Existing see-through type head-mounted display devices suffer from dark portions, striped brightness unevenness, enlargement of external images, and focus shift due to the design of the light guiding device, which includes a reflection unit with partially reflecting mirrors and a varying thickness that causes light path bending.
Innovation Solution
An optical element with a configuration of parallel mirrors, a first transmittance member between adjacent mirrors, and a second transmittance member on the incidence or exit side, where the mirrors are inclined and have varying widths to reduce dark portions and brightness unevenness, and the transmittance members help compensate for light path bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the reflectance of the partially reflecting mirror is increased to improve exit efficiency of image light, then a large dark portion is generated in the image
Solution Approach 1:
The patent applies local quality by varying the reflectance of individual mirrors along the light guiding body. Mirrors closer to the light source have higher reflectance to maximize image light extraction, while mirrors farther away have lower reflectance to prevent dark portions. This localized adjustment of optical properties resolves the contradiction between exit efficiency and image brightness uniformity.
Solution Approach 2:
The patent changes the reflectance parameter of mirrors along the length of the light guiding body. By gradually adjusting the reflectance value from higher to lower positions, the system optimizes both image light extraction efficiency and prevents excessive dark portions, resolving the technical contradiction through parameter optimization.
2Illumination intensity
If the interval between the partially reflecting mirrors is increased to reduce the dark portion, then striped unevenness in brightness is generated
Solution Approach 1:
The patent optimizes the interval parameter between mirrors by maintaining a consistent spacing that prevents both dark portions and striped brightness unevenness. This parameter optimization resolves the contradiction between brightness uniformity and the precision requirements of mirror arrangement.
3Productivity
If the thickness of the reflection unit is varied to improve light extraction, then the incidence surface and exit surface are not parallel causing light path bending
Solution Approach 1:
The patent segments the reflection unit into multiple independent mirror elements rather than using a single continuous varying-thickness structure. Each mirror segment can be precisely positioned and oriented, maintaining parallel incidence and exit surfaces while achieving effective light extraction through the segmented configuration.
4Reliability
If the reflecting unit is buried in the parallel light guiding body to protect it, then an inclined surface boundary exists causing light path bending and focus shift
Solution Approach 1:
The patent merges the reflection unit with the light guiding body by integrating mirrors directly into the light guiding structure. This integration eliminates the inclined surface boundary between separate components, preventing light path bending and focus shift while maintaining protection of the reflective elements within the unified structure.
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 reduces dark portions, striped brightness unevenness, and external image enlargement, while increasing exit efficiency and uniformity of brightness, and allows for easier manufacturing by allowing individual production of transmittance members.
Implementation Method 1
a plurality of mirrors that are provided in parallel to each other with an interval therebetween and reflect a part of image light and external image
Implementation Method 2
a light path of the external image is bent due to the difference in refractive index between the parallel light guiding body and the reflection unit
Data Source
AI summary
An optical element includes a plurality of mirrors; a first transmittance member interposed between adjacent two mirrors; and a second transmittance member provided on one of an incidence and an exit side of the image and the external image with respect to the first transmittance member. A surface of one transmittance member opposite to the other transmittance member among the first and the second transmittance member is an incidence surface on which the image and the external image are incident via a light guiding body. A surface of the other transmittance member is an exit surface from which the image and the external image are exited. Each of the plurality of mirrors is disposed so as to be inclined with respect to the incidence surface. The plurality of mirrors include a first and a second mirror whose width is narrower than a width of the first mirror.