Angle-Selective Transmission Filter for Near-Eye Display Stray Light
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Solution Overview
Problem
Designing optical systems for displays in virtual and augmented reality devices is challenging due to the need for components that are both aesthetically pleasing and optically efficient, while minimizing stray light to achieve optimal contrast and modulation transfer function (MTF).
Innovation Solution
The use of an angle-selective transmission filter (ASTF) interposed on the optical path, which filters emitted light as a function of angle, directing a first portion of the light along the optical path and redirecting a second portion of high-angle light outside the optical path, thereby minimizing stray light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional optical components are used in near-eye displays, then the device can be manufactured with standard components, but the components become unsightly and bulky while not achieving desired optical performance
Solution Approach 1:
The patent combines multiple optical functions (display, waveguide, input coupler, output coupler, imaging optics, and prism) into an integrated near-eye display system. This merging of components achieves the desired optical performance while reducing the overall bulkiness and improving aesthetics compared to using separate conventional components.
2Device complexity
If no angle-selective filtering is applied, then the optical path can be simpler, but stray light increases reducing contrast and MTF
Solution Approach 1:
The ASTF extracts and removes high-angle stray light from the optical path while allowing low-angle useful light to pass through. This selective extraction of harmful light components improves contrast and MTF without significantly complicating the overall optical path design.
3Illumination intensity
If the ASTF transmits all emitted light, then the display brightness is maximized, but stray light reduces contrast and optical performance
Solution Approach 1:
The ASTF applies angle-selective filtering properties to different portions of the emitted light based on their incident angles. Low-angle light (useful light) is transmitted with high transmission to maintain brightness, while high-angle light (stray light) is diffracted away. This local quality differentiation resolves the contradiction between maximizing brightness and eliminating stray light.
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 implementation of the ASTF optimizes the contrast and modulation transfer function (MTF) of the display by effectively filtering out stray light, resulting in improved optical performance and reduced bulkiness of the device components.
Implementation Method 1
The ASTF may include diffractive grating structures such as thin-film holograms, volume holograms (e.g., thin or thick volume holograms), or surface relief gratings, louvered mirrors, multi-layer coatings, or a pinhole array, as examples. The diffractive gratings may transmit the first portion of the emitted light while diffracting the second portion of the emitted light out of the optical path.
Implementation Method 2
A waveguide may be interposed on the optical path. An input coupler may couple the light into the waveguide. An output coupler may couple the light out of the waveguide and towards the eye box.
Data Source
AI summary
An electronic device may include an emissive display panel that emits light. The light may propagate along an optical path extending to an eye box. A waveguide with an input coupler and an output coupler may be interposed on the optical path. An angle-selective transmission filter (ASTF) may be interposed on the optical path and may filter the emitted light as a function of angle to remove high-angle light from the optical path before the light is provided to the output coupler. The ASTF may include diffractive grating structures such as thin-film holograms, volume holograms, or surface relief gratings, louvered mirrors, multi-layer coatings, or a pinhole array. This ASTF may serve to minimize stray light within the display, thereby optimizing the contrast and the modulation transfer function (MTF) of the display.