Directed Display Architecture for HMDs Using Microlens Arrays
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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 brightness and increased stray light, which causes the 'screen-door' effect and poor contrast, as the light is not directed towards the user's eyes.
Innovation Solution
A directed display with a microlens array that concentrates and directs the emission distributions of sub-pixels towards a target region, increasing the amount of light reaching the user and reducing stray light, while also masking the 'screen-door' effect by optically filling in the dead-space between pixels.
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 power is wasted and stray light increases
Solution Approach 1:
The patent applies local quality by making the emission distribution directionality location-dependent. The microlens array creates different emission patterns for different regions of the display, with each microlens directing light specifically toward the user's eye position. This allows the display to optimize light direction locally for each pixel region rather than using a uniform Lambertian pattern across the entire display, thereby reducing wasted off-axis light while maintaining adequate viewing angle.
Solution Approach 2:
The patent changes the emission distribution parameter from a fixed Lambertian pattern to a dynamic, directionally controlled pattern using microlenses. By introducing microlenses with specific focal lengths and orientations, the emission angle and direction parameters are modified to concentrate light toward the target eyebox region, reducing the solid angle of emission and minimizing energy waste while maintaining the required viewing characteristics.
2Adaptability or versatility
If a Lambertian emission distribution is used to maximize viewing angle, then the viewing angle is improved, but stray light increases reducing contrast
Solution Approach 1:
The microlens array creates location-specific emission patterns where each microlens directs light precisely toward the user's eye position. This local directional control prevents off-axis light from scattering within the HMD, eliminating the stray light problem that occurs with uniform Lambertian emission while preserving the wide viewing angle capability.
Solution Approach 2:
The patent converts the potentially harmful scattered light from Lambertian emission into beneficial directed light by using microlenses to refract and concentrate the emission. The microlenses take the omnidirectional Lambertian emission and transform it into focused beams directed at the eyebox, turning what would be wasted stray light into useful image-forming light that improves contrast.
3Area of stationary object
If conventional display is magnified to increase field of view, then the field of view is improved, but the screen-door effect appears
Solution Approach 1:
The patent changes the apparent size parameter of the emission areas through optical magnification. The microlens array, in combination with the optics block, magnifies the emission areas of individual pixels, making them appear larger to the user's eye. This optical magnification allows the display to achieve a larger effective field of view while preventing the dark spaces between pixels from becoming visible, thereby eliminating the screen-door effect.
4Illumination intensity
If microlens array concentrates emission distribution, then brightness is improved, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the display into individual pixel regions, each with its own microlens. This segmentation allows each microlens to independently concentrate light from its corresponding pixel or sub-pixel group, achieving high brightness through localized light concentration. The segmented approach with microlens arrays is a standard technique in display technology, balancing the brightness improvement against the added structural complexity in a practical manner.
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 solution enhances brightness uniformity across the display, reduces stray light, and mitigates the 'screen-door' effect by ensuring more light is directed towards the user's eyes, improving the overall display quality in HMDs.
Implementation Method 1
The microlens array is coupled to the electronic display and includes a plurality of microlenses. The microlens array is configured to concentrate the emission distributions of the sub-pixels to form concentrated image light
Implementation Method 2
The microlens array is configured to concentrate the emission distributions of the sub-pixels to form concentrated image light and direct the concentrated image light towards a target region
Data Source
AI summary
A head mounted display (HMD) includes an electronic display, a microlens array, and an optics block. The electronic display is composed of a plurality of sub-pixels, and each sub-pixel is configured to emit image light according to respective emission distribution. The microlens array is coupled to the electronic display and includes a plurality of microlenses. The microlens array concentrates the emission distributions of the sub-pixels to form concentrated image light and directs the concentrated image light towards a target region. The optics block is positioned in the target region. The optics block is configured to direct the concentrated 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.