Light-Guide Optical Element with Partially-Reflecting Surfaces
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Solution Overview
Problem
Existing optical systems using compound Light-Guide Optical Elements (LOEs) face challenges in achieving efficient optical aperture expansion for near-eye displays, particularly in ensuring uniform image illumination and minimizing dark stripes caused by internal reflections.
Innovation Solution
The optical system employs a light-guide optical element (LOE) with a first region containing a set of planar, mutually-parallel, partially-reflecting surfaces oriented orthogonally to the major external surfaces, and a second region with a second set of partially-reflecting surfaces at an oblique angle, ensuring efficient image redirection and coupling out towards the user.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the second set of partially-reflecting surfaces extends across the full thickness of the LOE, then more light can be coupled out towards the user, but dark stripes appear due to internal reflections at the major external surfaces
Solution Approach 1:
The patent extracts the second set of partially-reflecting surfaces from the surface layers of the LOE by positioning them to extend across less than 95% of the thickness. This extraction removes the harmful interaction between these surfaces and the major external surfaces, eliminating the dark stripe problem while preserving the light coupling function.
Solution Approach 2:
The patent introduces an intermediary spacing between the second set of partially-reflecting surfaces and the major external surfaces. This spacing acts as a mediator that prevents direct optical interaction between the two sets of surfaces, thereby eliminating the harmful internal reflections that cause dark stripes while maintaining the desired light coupling effect.
2Ease of manufacture
If the first set of partially-reflecting surfaces extends across less than full thickness, then manufacturing is easier, but image illumination uniformity decreases
Solution Approach 1:
The patent applies local quality by differentiating the thickness extension of the two sets of partially-reflecting surfaces. The first set extends across at least 95% of the thickness to maintain image illumination uniformity, while the second set extends across less than 95% to avoid dark stripes. This localized differentiation optimizes both manufacturing ease and optical performance.
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 effective optical aperture expansion, enhances image uniformity by minimizing dark stripes, and improves the overall quality of the viewed image in near-eye displays.
Implementation Method 1
image illumination propagating within the LOE by internal reflection at the major external surfaces
Implementation Method 2
image illumination propagating within the LOE by internal reflection at the major external surfaces from the first region into the second region is coupled out of the LOE towards the user
Data Source
AI summary
An optical system for directing image illumination injected at a coupling-in region towards a user for viewing includes a light-guide optical element (LOE) (12) with a pair of parallel major external surfaces (24). A first region (16) of the LOE contains a first set of partially-reflecting surfaces (17) oriented to redirect image illumination propagating within the LOE towards a second region of the LOE (18), which contains a second set of partially-reflecting surfaces (19) oriented to couple out the image illumination towards the user. The first set of partially-reflecting surfaces (17) extend across at least 95 percent of a thickness of the LOE, while the second set of partially-reflecting surfaces (19) are contained within a subsection of the thickness spanning less than 95 percent of the thickness, so that the second set of partially-reflecting surfaces (19) are excluded from one or both surface layers of the second region (18).