AR Display With Internal Partial Reflectors for Compact Design
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Solution Overview
Problem
Existing augmented reality displays, particularly near-eye displays, face challenges in achieving compact designs while maintaining undistorted visibility of the real world due to geometrical requirements of beam splitters and precision needs of light-guide substrates.
Innovation Solution
A display system employing a partially transparent optical element with internal, planar, and mutually parallel partially reflective surfaces that redirect collimated image illumination at high angles, allowing for compact designs and reduced sensitivity to optical surface imperfections, using free-space projection and polarization-selective facets for image delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a beam splitter architecture with an oblique partial reflector is used to project virtual images while enabling real-world visibility, then the augmented reality display function is achieved, but the structure becomes bulky due to geometrical requirements
Solution Approach 1:
The patent transitions from a traditional 2D beam splitter configuration to a 3D volumetric optical element with multiple internal reflective surfaces. The optical element contains several partial reflectors arranged in three-dimensional space, allowing light to be reflected multiple times within the volume to achieve the desired image projection while maintaining a compact external form factor.
Solution Approach 2:
The optical element embeds multiple partial reflective surfaces within its internal structure. These nested reflective surfaces are positioned at different depths and orientations within the optical element, allowing each surface to contribute to the overall image projection function while the entire assembly maintains a compact external dimension.
2Volume of moving object
If a light-guide optical element with total internal reflection is used to trap and couple out images, then compact design is achieved, but high precision parallelism of optical surfaces is required to preserve image quality
Solution Approach 1:
The patent replaces the reliance on precise mechanical alignment of optical surfaces with a system that uses multiple internal reflective surfaces at controlled angles. Instead of requiring high-precision parallelism of entry and exit surfaces, the design uses angularly oriented partial reflectors that can tolerate greater manufacturing variations while maintaining image quality.
Solution Approach 2:
The patent changes the operational parameters from relying on near-perfect parallelism (high precision requirement) to using controlled angular orientations of multiple reflective surfaces. This parameter change allows the system to achieve the same light guidance function with relaxed manufacturing tolerances for surface parallelism.
3Volume of moving object
If multiple internal partial reflectors are used to redirect light rays, then compact design and reduced surface precision requirements are achieved, but chromatic aberration and aperture limitations arise
Solution Approach 1:
The patent divides the optical element into multiple segments, each containing partial reflective surfaces that handle specific portions of the light spectrum or angular ranges. This segmentation allows each surface to be optimized for its specific function, and the combined effect of all segments produces a high-quality image with reduced chromatic aberration through systematic correction.
Solution Approach 2:
The patent introduces intermediate optical elements or coating layers between the partial reflective surfaces to compensate for chromatic aberration. These intermediary elements act as mediators that correct wavelength-dependent deviations introduced by the multiple reflections, thereby maintaining image quality while preserving the compact multi-surface architecture.
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 approach enables more compact and flexible design options for augmented reality displays, improving image quality and reducing bulkiness while maintaining clear real-world visibility, with enhanced chromatic aberration compensation and aperture expansion capabilities.
Implementation Method 1
an optical element formed from at least partially transparent material having first and second major surfaces, the optical element including a plurality of partially reflective surfaces, the plurality of partially reflective surfaces being internal to the optical element
Implementation Method 2
an optical element formed from at least partially transparent material having first and second major surfaces
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3D
AI summary
A display has an image projector projecting collimated image illumination along a projection direction, and an optical element having two major surfaces and containing partially reflective surfaces which are internal to the optical element, planar, mutually parallel and overlapping relative to the projection direction. Each ray of the collimated image illumination enters the optical element and is partially reflected by at least two of the partially reflective surfaces so as to be redirected to exit the first major surface along a viewing direction. An alternative implementation; a first reflection from one of the partially reflective surfaces redirects part of the image illumination rays so as to undergo total internal reflection at the major surfaces of the optical element. The rays are then redirected by further reflection from another of the partially reflective surfaces to exit the optical element along the viewing direction.