HMD Optical System Ghost Reduction via Asymmetric Color Filters
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Head-mounted displays (HMDs) with ocular optical systems that utilize polarization of light face challenges in achieving wide view angles while maintaining luminance and chromaticity, as the short focal length and birefringence in plastic lenses lead to ghosting and deteriorated viewing angle characteristics, especially at marginal view angles.
Innovation Solution
The implementation of a configuration that includes a display element with a central portion having higher luminance in the normal direction than in the specific direction, and an edge portion with lower luminance in the normal direction than in the specific direction, utilizing a first and second phase plate, a semi-transmissive reflective surface, and a polarization beam splitter to control light polarization and reduce ghosting, along with shifting color filters relative to sub-pixels to improve viewing angle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a short focal length ocular optical system is used to achieve wide view angle, then the view angle is improved, but the luminance and chromaticity characteristics at marginal view angles deteriorate
Solution Approach 1:
The patent applies local quality by making the color filters have different sizes at different positions on the display element. Specifically, the color filters at the marginal portion (edge) of the display element are made larger than those at the central portion. This local variation in filter size compensates for the deteriorated viewing angle characteristics at the edges caused by the short focal length, while maintaining good characteristics at the center.
2Weight of moving object
If a plastic lens is used to reduce weight, then the weight is reduced, but ghost is generated due to birefringence
Solution Approach 1:
The patent applies parameter changes by deliberately adjusting the relative positions of the color filters and sub-pixels. The color filters are positioned such that their centers do not coincide with the centers of the corresponding sub-pixels, but are offset by specific distances in specific directions. This positional parameter adjustment compensates for the ghosting effect caused by birefringence in the plastic lens, allowing the use of lightweight plastic materials while reducing ghost visibility.
3Manufacturing precision
If color filters are positioned with centers coinciding with sub-pixel centers, then normal direction viewing characteristics are improved, but ghost due to lens birefringence cannot be reduced
Solution Approach 1:
The patent applies asymmetry by intentionally creating an asymmetric relationship between color filter positions and sub-pixel positions. Instead of symmetric alignment (centers coinciding), the color filters are positioned asymmetrically relative to the sub-pixels, with specific offset distances and directions. This asymmetric positioning serves dual purposes: maintaining acceptable normal direction viewing characteristics while compensating for ghosting effects from lens birefringence.
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 enhances viewing angle characteristics by reducing ghosting and improving luminance and color shift at marginal view angles, allowing for a wider view angle while maintaining image quality and reducing the intensity of ghost light.
Implementation Method 1
an ocular optical system that folds an optical path by utilizing polarization of light
Implementation Method 2
a semi-transmissive reflective surface
Implementation Method 3
a lens
Implementation Method 4
a polarization state of light is disturbed by birefringence in the plastic lens, which results in generation of ghost
Data Source
AI summary
The image display apparatus includes an optical system configured to introduce light from a display surface of a display element to an observer. The optical system includes in order from the display element toward the observer, a first phase plate, a semi-transmissive reflective surface, a lens, a second phase plate, and a polarization beam splitter. The display element is configured to make, at a central portion of the display surface, luminance in a normal direction in which a normal to the display surface extends higher than that in a specific direction tilted outward with respect to the normal direction, and to make, at a most edge portion of the display surface, the luminance in the normal direction lower than that in the specific direction.