Light-Guide Reflector Layout for Finite-Depth Near-Eye Images
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Solution Overview
Problem
Near-eye display systems using waveguides inherently generate collimated images at infinity, making it difficult to achieve the required apparent depth for images projected towards the observer, which increases the dimensions of the waveguide and projector, and limits the field of view.
Innovation Solution
Incorporating a reflector in the light-guide display system to reflect the coupled-out image back towards the observer, allowing for reduced eye relief and enabling adjustable apparent image depth, with options for polarization-selective, chromatically-selective, or convex reflectors, and their integration with refractive lenses for enhanced functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If refractive lenses are introduced to implement apparent depth in waveguide-based displays, then the required apparent depth is achieved, but the waveguide must be located further from the eye, increasing the dimensions of the waveguide and projector
Solution Approach 1:
Instead of using refractive lenses to converge light towards the eye (forward approach), the patent uses reflective surfaces to redirect light back through the waveguide (reverse approach). This inversion of the optical path allows the waveguide to remain close to the eye while still achieving the required apparent depth, resolving the contradiction between apparent depth and waveguide dimension.
2Ease of operation
If refractive lenses are introduced to generate virtual image at finite distance, then the virtual image appears at desired distance, but the field of view is limited
Solution Approach 1:
The patent transitions from using refractive lenses (which work in one dimension of light convergence) to using reflective surfaces that can manipulate light in multiple dimensions. The reflective configuration allows for broader angular acceptance and exit, expanding the field of view while maintaining virtual image at finite distance through geometric reflection rather than refraction.
3Device complexity
If coupling-out arrangement reflects image towards observer directly, then simple optical path is achieved, but eye relief is increased and device size increases
Solution Approach 1:
The patent implements a nested optical configuration where the reflective surface is positioned within or integrated with the waveguide structure. The light path is folded back through the waveguide itself, nesting the reflection function within the existing waveguide geometry. This allows the optical path to remain simple while minimizing eye relief, as the reflected light retraces part of its path through the compact waveguide structure.
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 configuration reduces the size of the light-guide and projector, allows for adjustable apparent image depth, and facilitates integration with conventional spectacles, providing improved rendering of images with multiple levels of depth and reduced power loss, while maintaining visibility of the real scene.
Implementation Method 1
Projector 10a injects image light collimated to infinity into a light-guide optical element or 'LOE' (interchangeably referred to as a 'waveguide') 20 so as to propagate by total internal reflection (TIR) within the waveguide
Implementation Method 2
A coupling-out arrangement is exemplified here by partially reflecting internal surfaces (interchangeably referred to as 'facets') 22a within the waveguide oriented at an oblique angle to the major parallel surfaces of the waveguide so as to reflect the light 24a towards the observer's eye 26
Implementation Method 3
a reflector deployed to reflect the coupled-out image back through the LOE towards the eye of the observer
Data Source
AI summary
A display includes a light-guide optical element (LOE) (20) and a projector arrangement (10a) for injecting an image into the LOE so as to propagate within the LOE by internal reflection at a pair of major faces. The image is coupled out from the LOE by a coupling-out arrangement, exemplified here as internal partially-reflecting surfaces (22b). The image is coupled out from the LOE in a direction away from the eye of the observer (24b), and a reflector (30) reflects the coupled-out image back through the LOE (32), towards the eye of the observer (26). Reflector (30) is preferably a selective partial reflector, and may be convex to provide a desired apparent image distance.