Embedded Beam Splitter LOE for Uniform Large-Aperture Projection
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Solution Overview
Problem
Optical systems for near-eye displays and head-up displays face challenges in achieving uniform image projection over a large aperture while maintaining a compact device form factor, as existing solutions either require large image projectors or additional beam multiplying arrangements that increase device size.
Innovation Solution
The use of a light-guide optical element (LOE) with internal planar beam splitters and partially reflecting surfaces, configured to overlap with the coupling-out region, allows for uniform image illumination distribution without increasing the device's overall size by embedding a beam multiplying region within the LOE.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a large aperture is used to cover the eye-motion box area, then uniform image projection is achieved, but the device size increases
Solution Approach 1:
The beam multiplying region is embedded within the light-guide optical element, nesting one optical function inside another. The beam splitter and coupling-out surfaces are integrated into the LOE structure, allowing beam multiplication without increasing the overall device volume, thus resolving the contradiction between large aperture and compact device size.
Solution Approach 2:
The invention uses internal reflection within the LOE to propagate image illumination in a folded optical path, effectively utilizing the thickness dimension of the LOE to achieve aperture expansion without increasing the lateral footprint of the device.
2Manufacturing precision
If additional beam multiplying arrangements are added, then uniform image projection is achieved, but device complexity increases
Solution Approach 1:
The beam multiplying function and the light guiding function are merged into a single integrated component (the LOE with embedded beam splitter). This consolidation achieves uniform image projection through beam multiplication while reducing device complexity by eliminating the need for separate beam multiplying arrangements.
Solution Approach 2:
The light-guide optical element serves multiple functions simultaneously: it guides light from the projector, performs beam multiplication through internal reflection at the beam splitter, and directs the expanded beam to the eye-motion box. This multi-functionality reduces overall system complexity while achieving uniform image projection.
3Area of stationary object
If the image projector size is increased, then uniform image projection over large aperture is achieved, but the compact device form factor is compromised
Solution Approach 1:
The beam splitting and coupling-out surfaces are nested within the LOE structure, allowing a small projector to generate an enlarged virtual image that uniformly covers the eye-motion box area without requiring a physically large projector.
Solution Approach 2:
The LOE uses its thickness dimension to create a folded optical path with multiple internal reflections, effectively multiplying the image aperture in the lateral dimensions while the projector itself remains compact.
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 ensures uniform image projection over a large aperture while maintaining a compact design, achieving efficient optical aperture expansion in one or two dimensions, depending on the LOE implementation.
Implementation Method 1
a pair of major external surfaces that are parallel so as to support propagation of the image illumination within the LOE by internal reflection at the major external surfaces
Implementation Method 2
a coupling-out configuration associated with a coupling-out region of the LOE and configured for coupling out at least part of the image illumination from the LOE towards the eye-motion box, the coupling-out configuration including a plurality of mutually-parallel partially reflecting surfaces
Implementation Method 3
at least one planar beam splitter internal to the LOE and parallel to the major external surfaces, the at least one planar beam splitter at least partially extending into the coupling-out region so as to overlap with some but not all of the mutually-parallel partially reflecting surfaces
Data Source
AI summary
An optical system has a light-guide optical element (LOE) with a pair of parallel major external surfaces that support propagation of image illumination within the LOE by internal reflection at the major external surfaces. A plurality of mutually-parallel partially reflecting surfaces is deployed within a coupling-out region of the LOE obliquely to the major external surfaces, and couples out at least part of the image illumination from the LOE towards an eye-motion box. In an embodiment, a planar homogenizer is internal to the LOE and parallel to the major external surfaces, and at least partially extends into the coupling-out region so as to overlap with some but not all of the mutually-parallel partially reflecting surfaces. In another embodiment, the LOE includes a second plurality of mutually-parallel partially reflecting surfaces, and the homogenizer is alternatively deployed in overlapping relation with the second plurality of mutually-parallel partially reflecting surfaces.