Three-Stage LOE Aperture Expansion for Uniform Illumination
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Solution Overview
Problem
Existing optical systems for near-eye displays face challenges in achieving uniform image illumination across a wide optical aperture while balancing projector size and production complexity, particularly in reconciling the need for a compact projector with efficient aperture expansion.
Innovation Solution
The optical system employs a three-stage expansion mechanism using partially-reflecting surfaces with successively-increasing reflectivities, where a preliminary set of facets expands the aperture before a main set, followed by a coupling-out mechanism, to achieve uniform illumination and reduce production complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a single-stage aperture expansion using orthogonal facets is used, then the optical aperture can be expanded, but the image illumination becomes non-uniform and production complexity increases
Solution Approach 1:
The aperture expansion is divided into three distinct stages using three separate sets of facets (first set with lower reflectivity, second set with medium reflectivity, third set with higher reflectivity). Each stage progressively expands the aperture while managing illumination uniformity, avoiding the need for a single complex high-reflectivity facet array that would be difficult to manufacture.
Solution Approach 2:
Different regions of the waveguide are assigned different facet reflectivity characteristics. The first set of facets has lower reflectivity to capture and redirect initial light, the second set has medium reflectivity for intermediate expansion, and the third set has higher reflectivity for final aperture enlargement. This localized variation in optical properties optimizes both uniformity and manufacturability.
2Area of stationary object
If high-reflectivity facets are used to expand aperture, then aperture size increases, but image illumination uniformity deteriorates
Solution Approach 1:
The first set of facets with lower reflectivity performs a preliminary light redistribution function before the light reaches the higher-reflectivity third set of facets. This preliminary action pre-conditiones the illumination distribution, preventing the high-reflectivity facets from creating severe non-uniformity while still achieving aperture expansion.
3Volume of moving object
If projector size is reduced for compactness, then device portability improves, but aperture expansion efficiency decreases
Solution Approach 1:
Instead of expanding aperture in a single dimension through a large projector, the system uses three sets of facets arranged in sequential stages that expand the aperture in multiple directions and dimensions within the waveguide. This multi-dimensional approach allows a compact projector to achieve effective aperture expansion through the cumulative effect of multiple reflection stages.
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 allows for a larger optical aperture with uniform image intensity, reducing production costs and complexity by optimizing facet spacing and reflectivity sequences, enhancing the display's efficiency and ergonomic design.
Implementation Method 1
conveys an image within the LOE by internal reflection
Implementation Method 2
the propagating image being partially reflected by the first set of partially-reflecting surfaces to generate a deflected propagating image
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
An optical system including a light-guide optical element (LOE) with first and second sets (204, 206) of mutually-parallel, partially-reflecting surfaces at different orientations. Both sets of partially-reflecting surfaces are located between parallel major external surfaces. A third set of at least partially-reflecting surfaces (202), deployed at the coupling-in region, receive image illumination injected from a projector (2) with an optical aperture having a first in-plane width and direct the image illumination via reflection of at least part of the image illumination at the third set of at least partially-reflective facets towards the first set of partially-reflective facets with an effective optical aperture having a second width larger than the first width.