Light-Guide Optical Elements for Two-Dimensional Aperture Expansion
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Solution Overview
Problem
Existing near-eye display systems face challenges in achieving effective optical aperture expansion and efficient image coupling to enhance the field of view, particularly in virtual and augmented reality applications.
Innovation Solution
The optical system employs a light-guide optical element (LOE) with two sets of planar, mutually-parallel partially-reflecting surfaces oriented at different angles, integrated with a set of major external surfaces, to redirect and couple out image illumination towards the eye-motion box, utilizing a first set of facets for initial deflection and a second set for final coupling, with variable spacing and selective coating to optimize image projection.
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 optical path is simple, but the field of view and aperture expansion are limited
Solution Approach 1:
The patent introduces a second dimension to the optical path by adding a second set of parallel reflecting surfaces oriented at a different angle to the first set. This multi-dimensional arrangement of reflective surfaces enables light to undergo multiple reflection events at different orientations, thereby expanding the optical aperture and field of view without simply increasing the size of a single reflective element.
Solution Approach 2:
The optical system is segmented into multiple functional regions within the LOE, with each set of reflecting surfaces serving a specific purpose in the light propagation path. The first set of surfaces performs initial reflection and direction control, while the second set performs additional reflection to achieve the desired output coupling, dividing the complex optical function into manageable segments.
2Area of stationary object
If multiple reflecting surfaces are added to expand aperture, then the field of view increases, but unwanted reflections and image quality degradation occur
Solution Approach 1:
The patent applies the principle of local quality by implementing non-uniform spacing between the reflecting surfaces, with closer spacing near the coupling-in region and wider spacing further away. This localized variation in geometric parameters optimizes the reflection pattern at different positions, directing desired light paths while minimizing unwanted reflections and maintaining image quality across the expanded aperture.
3Ease of manufacture
If uniform spacing between reflecting surfaces is used, then manufacturing is simple, but image uniformity across the field of view is poor
Solution Approach 1:
The patent implements non-uniform spacing between reflecting surfaces, with closer spacing near the coupling-in region and wider spacing further away. This localized variation in geometric parameters optimizes the reflection pattern at different positions, directing desired light paths while minimizing unwanted reflections and maintaining image quality across the expanded aperture.
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 achieves compact and efficient optical aperture expansion, enhancing the field of view and image quality in near-eye displays by optimizing the use of reflective surfaces and reducing unnecessary reflections, thereby improving image uniformity and reducing system size.
Implementation Method 1
image illumination propagating within the LOE by internal reflection at the major external surfaces
Implementation Method 2
first set of planar, mutually-parallel, partially-reflecting surfaces having a first orientation
Data Source
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.