Stepped Waveguide Near-Eye Display for Pupil Tracking
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Solution Overview
Problem
Current head-worn displays for virtual, augmented, and mixed reality struggle to provide high-resolution, high-luminance, and high-contrast images with wide fields of view in a thin, lightweight, and cost-effective form factor, while also managing power efficiency and reducing stray light and heat dissipation.
Innovation Solution
A near-eye display apparatus featuring a directional backlight with a waveguide, spatial light modulator, and magnifying lens, which includes an array of light sources and stepped facets for efficient light guidance and modulation, along with a pupil detection system to optimize illumination and reduce stray light, thereby enhancing image uniformity and contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional backlight system is used to provide high luminance output, then the brightness is improved, but the thickness and weight increase
Solution Approach 1:
The waveguide is segmented into multiple sections with different facet structures: a first section with extraction facets at an first angle and a second section with extraction facets at a second angle. This segmentation allows different portions of the waveguide to optimize for different functions, achieving high luminance output while maintaining thin overall thickness.
Solution Approach 2:
Different regions of the waveguide are given different local properties: the first section has facets oriented at a first angle optimized for extracting light in one direction, while the second section has facets at a second angle optimized for extracting light in another direction. This local quality variation enables the thin waveguide to provide directionally controlled high luminance output.
2Area of stationary object
If light sources are distributed across the waveguide to illuminate the entire eyebox, then the field of view is improved, but stray light and heat dissipation increase
Solution Approach 1:
The waveguide is divided into sections with different facet orientations that direct light locally to specific regions of the eyebox. This localized light direction reduces stray light by ensuring light is directed only where needed, and reduces heat dissipation by minimizing unnecessary light propagation paths.
Solution Approach 2:
The patent converts what would normally be stray light (harmful) into beneficial directed illumination by using the stepped facets to reflect and redirect light that would otherwise be lost. The facets are specifically oriented to bounce light toward the eyebox while preventing it from reaching non-imaging surfaces, thereby converting potential stray light into useful illumination.
3Illumination intensity
If the waveguide extraction facets are oriented to maximize light output, then the luminance is improved, but image uniformity across the eyebox deteriorates
Solution Approach 1:
The waveguide is segmented into multiple sections, each with facets oriented at different angles. The first section extracts light at an first angle and the second section extracts light at a second angle, creating an integrated light distribution that maintains high overall luminance while achieving uniform illumination across the entire eyebox.
Solution Approach 2:
Different sections of the waveguide have locally optimized facet orientations tailored to their specific function: some sections prioritize maximum light extraction while others prioritize uniform distribution. This local quality optimization allows the overall system to achieve both high luminance and uniform image quality.
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 increases power efficiency, reduces battery size and weight, extends battery life, and enhances image contrast and uniformity across the eyebox, achieving high dynamic range operation while maintaining a thin form factor and low manufacturing complexity.
Implementation Method 1
the first guide surface being arranged to guide light by total internal reflection
Implementation Method 2
a plurality of facets oriented to extract the light from the light sources, after reflection from the reflective end, out of the waveguide through the first guide surface
Data Source
AI summary
A near-eye display apparatus comprises a spatial light modulator illuminated by a directional backlight and a magnifying lens arranged to provide a magnified wide field of view image to an eye of a user. The directional backlight comprises an array of light sources and a stepped waveguide comprising a curved reflective end. Light propagates along the waveguide without loss and is reflected from the reflective end. The steps of the waveguide are arranged to provide a virtual optical window for each light source. The magnifying lens images the virtual optical window to a real pupil window in an eyebox. The real pupil window may be steered in response to the measured location of the user's pupil. High illumination efficiency is provided to the user in a thin form factor.