Directed Display Architecture for HMDs
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Solution Overview
Problem
Conventional display technology in head-mounted displays (HMDs) wastes power due to a Lambertian emission distribution, leading to reduced light efficiency and increased stray light, which causes the 'screen-door' effect and poor contrast, as it is designed for wide viewing angles rather than focused directional emission.
Innovation Solution
A directed display with a microlens array that concentrates the emission distribution of sub-pixels or pixels towards a target region, increasing light efficiency and reducing stray light by directing more light to the user's eyes while masking the 'screen-door' effect through diffusing microlenses that create blur spots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a Lambertian emission distribution is used to maximize viewing angle, then the viewing angle is improved, but light efficiency deteriorates due to wasted off-axis light
Solution Approach 1:
The patent applies local quality by making each microlens individually optimized to control the emission pattern of its corresponding pixel or sub-pixel. Each microlens creates a localized directional emission pattern tailored to direct light toward the eyebox, rather than using a uniform Lambertian pattern across the entire display. This localized control resolves the contradiction by maintaining adaptability for the specific viewing direction while dramatically improving light efficiency.
Solution Approach 2:
The patent changes the emission parameter from a broad Lambertian distribution to a focused directional distribution through the microlens array. By modifying the emission angular distribution parameter through optical transformation, the system directs light preferentially toward the eyebox region, resolving the contradiction between viewing angle requirements and light efficiency by changing how light is distributed in space.
2Stability of the object's composition
If a Lambertian emission distribution is used, then the emission uniformity is improved, but stray light increases reducing contrast
Solution Approach 1:
Each microlens creates a localized controlled emission pattern that directs light precisely toward the eyebox while suppressing off-axis emission. This local control eliminates stray light generation without compromising the uniformity of the displayed image, as each pixel's light is uniformly directed toward the intended viewing zone. The local quality principle resolves the contradiction by maintaining emission consistency while eliminating harmful stray light.
3Area of stationary object
If conventional displays are magnified to increase field of view, then the field of view is improved, but the screen-door effect worsens due to visible dead-space between emission points
Solution Approach 1:
The microlens array acts as an intermediary optical element between the display pixels and the user's eye. It transforms the emission pattern of each pixel to fill the angular space between adjacent pixels, effectively masking the dead-space that causes the screen-door effect. This intermediary component enables field of view expansion through magnification while eliminating the visual artifacts that would otherwise become apparent.
4Adaptability or versatility
If off-axis light is emitted to maximize viewing angle, then the viewing flexibility is improved, but power waste increases
Solution Approach 1:
The microlens array implements local quality control at each pixel level, directing light preferentially toward the eyebox region where the user's eye is located. This localized directional control eliminates wasteful off-axis emission while maintaining the ability to provide viewing flexibility within the intended eyebox volume. The system achieves power efficiency by making each pixel's emission locally optimized for its intended viewing direction.
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 enhances light power and uniformity across the display, reduces stray light, and mitigates the 'screen-door' effect by directing emission towards the user's eyes, resulting in improved brightness and contrast without compromising the eyebox size.
Implementation Method 1
The microlens array includes a plurality of microlenses, and is affixed such that each microlens concentrates an emission distribution from a corresponding single sub-pixel (or pixel in some embodiments)
Implementation Method 2
masking the 'screen-door' effect through diffusing microlenses that create blur spots
Data Source
AI summary
A head-mounted display (HMD) includes an electronic display element, a microlens array, and an optics block. The electronic display element outputs image light via sub-pixels having different colors, the sub-pixels separated from each other by a dark space region. The sub-pixels have associated emission distributions that describe ranges of angles of light emitted from the plurality of sub-pixels. The microlens array includes microlenses that are each coupled to at least one corresponding sub-pixel, of the sub-pixels, where the microlenses concentrate the emission distributions and direct the emission distributions toward a target region. The optics block, which is located in the target region optically corrects the image light and directs the optically corrected image light from the microlens array to an exit pupil of the HMD corresponding to a location of an eye of a user of the HMD.