Light-Guide Optical Element Layout for 2D Aperture Expansion
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Solution Overview
Problem
Existing near-eye display systems face challenges in efficiently expanding the optical aperture to provide a wide field of view while maintaining compactness and reducing ghost reflections.
Innovation Solution
The optical system employs a light-guide optical element (LOE) with distinct regions of planar, partially-reflecting surfaces oriented at different angles, coupled with a collimated image projector, to achieve two-dimensional optical aperture expansion and minimize ghost reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a single set of parallel reflecting surfaces is used in the LOE, then the structure is simple and compact, but the optical aperture expansion is limited and field of view is narrow
Solution Approach 1:
The LOE is divided into multiple distinct regions (first region with first set of parallel surfaces, second region with second set of surfaces at oblique angle, third region with third set of surfaces) instead of using a single uniform structure. This segmentation allows each region to contribute differently to optical aperture expansion in different directions, achieving two-dimensional expansion while maintaining overall structural integration.
Solution Approach 2:
The patent transitions from one-dimensional aperture expansion (single set of parallel surfaces) to two-dimensional aperture expansion by introducing surfaces at multiple orientations (first set parallel to each other, second set at oblique angle, third set at different oblique angle). This multi-orientation arrangement expands the effective optical aperture in multiple spatial dimensions simultaneously.
2Area of stationary object
If multiple sets of reflecting surfaces at different orientations are introduced to expand optical aperture, then field of view is widened, but ghost reflections increase
Solution Approach 1:
Each region of the LOE is designed with specific surface orientations and optical properties tailored to its function. The first region has surfaces optimized for one direction of light propagation, the second region has surfaces at oblique angles for another direction, and the third region has surfaces for a third direction. This local optimization ensures that each surface set reflects light efficiently in its intended direction while minimizing unwanted reflections from other directions.
Solution Approach 2:
The patent strategically positions and orients the multiple sets of reflecting surfaces so that potential ghost reflections from one region are redirected into useful light paths by subsequent regions. The oblique angle surfaces are designed to capture and redirect stray light that would otherwise create ghost images, converting potentially harmful reflections into beneficial light guidance toward the eye.
3Manufacturing precision
If the LOE uses extensive bonding to form optical continuum, then manufacturing precision is improved, but manufacturing complexity increases
Solution Approach 1:
The LOE is constructed by bonding together multiple separately manufactured plate structures, each containing specific sets of reflecting surfaces. This segmentation allows each plate to be manufactured and precision-bonded independently, then assembled into the final multi-region structure. The bonding interfaces are designed to create optical continua between plates while maintaining the distinct functional regions.
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 system effectively expands the optical aperture in two dimensions, enhancing the field of view while reducing the system's size and minimizing unwanted reflections, resulting in improved image clarity and efficiency.
Implementation Method 1
image illumination propagating within the LOE by internal reflection at the major external surfaces
Implementation Method 2
partially-reflecting surfaces having a first orientation... partially-reflecting surfaces are oriented so that a part of image illumination propagating within the LOE by internal reflection
Data Source
Figure 1A~1B
Figure 2A
Figure 2B
AI summary
An optical system including a light- guide optical element (LOE) with a first set of mutually-parallel, partially-reflecting surfaces and a second set of mutually-parallel, partially-reflecting surfaces at a different orientation from the first set. Both sets of partially-reflecting surfaces are located between a set of mutually-parallel major external surfaces. Image illumination introduced at a coupling-in location propagates along the LOE, is redirected by the first set of partially-reflecting surfaces towards the second set of partially-reflecting surfaces, where it is coupled out towards the eye of the user. The first set of partially-reflecting surfaces are implemented as partial surfaces located where needed for filling an eye-motion box with the required image. Additionally, or alternatively, spacing of the first set of partially-reflecting surfaces is varied across a first region of the LOE. Additional features relate to relative orientations of the projector and partially reflecting surfaces to improve compactness and achieve various adjustments.