Compact Optical System for Head-Mounted Devices Using Curved Lens Elements
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Solution Overview
Problem
Current head-mounted devices, particularly those used for virtual reality (VR), augmented reality (AR), and mixed reality (MR), face challenges in achieving high image quality while being compact and lightweight, due to limitations in lens combinations and image projection techniques.
Innovation Solution
The optical system comprises an image surface, an aperture stop, quarter-wave plates, a partial reflector, a reflective polarizer, and two optical lens elements with specific surface curvatures and refractive powers, which work together to reduce the overall length of the optical system while maintaining high image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If Fresnel lenses are used in VR head-mounted devices, then the focal length can be reduced, but image quality deteriorates
Solution Approach 1:
The optical system is divided into multiple lens elements (first optical lens element and second optical lens element) with specific curvature relationships. This segmentation allows each element to contribute to both focal length reduction and image quality maintenance, avoiding the quality degradation associated with Fresnel lenses while achieving compact focal length.
Solution Approach 2:
The patent employs a composite optical structure combining multiple lens elements with different curvature characteristics. The first lens element has a convex front-side surface while the second lens element has a concave rear-side surface, creating a composite optical system that achieves short focal length without sacrificing image quality.
2Volume of moving object
If the optical system is made compact, then the device size and weight are reduced, but image quality may deteriorate
Solution Approach 1:
The patent utilizes specific curvature relationships between lens surfaces, particularly the condition where the absolute ratio of curvature radii |R3|/|R4| > 1.2. This curvature optimization enables compact lens element design while maintaining proper light focusing and image quality, resolving the trade-off between compactness and image quality.
Solution Approach 2:
The patent optimizes specific optical parameters including the curvature radius ratio condition |R3|/|R4| > 1.2 and the placement of wave plates and polarizers. These parameter changes enable the optical system to achieve compact dimensions while preserving image quality through precise control of light propagation and polarization.
3Manufacturing precision
If multiple optical components (wave plates, polarizers) are added to improve image quality, then the device complexity increases
Solution Approach 1:
The patent integrates multiple optical components (first quarter-wave plate, partial reflector, second quarter-wave plate, reflective polarizer) into a unified optical path configuration. By merging these components with the lens elements in a specific arrangement, the system achieves high image quality while managing complexity through integrated design rather than separate assemblies.
Solution Approach 2:
The optical components serve multiple functions simultaneously: the quarter-wave plates handle polarization transformation, the partial reflector manages light distribution, and the reflective polarizer controls polarization state. This multi-functionality reduces the need for additional separate components, managing overall system complexity while maintaining high image quality.
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 allows for a compact optical system that provides high image quality, reduces user dizziness, and enhances the immersive experience by optimizing the curvature radii of lens elements and the placement of wave plates and polarizers.
Implementation Method 1
The first quarter-wave plate is located between the image surface and the aperture stop. The second quarter-wave plate is located between the partial reflector and the aperture stop.
Implementation Method 2
The partial reflector has an average light reflectivity of at least 35%, and the partial reflector is located between the first quarter-wave plate and the aperture stop.
Implementation Method 3
The reflective polarizer is located between the second quarter-wave plate and the aperture stop.
Implementation Method 4
The first optical lens element is located between the image surface and the aperture stop and has a front-side surface being convex. The second optical lens element is located between the first optical lens element and the aperture stop and has a rear-side surface being concave.
Data Source
AI summary
An optical system includes an image surface, an aperture stop, a first and a second quarter-wave plate, a partial reflector, a reflective polarizer, a first and a second optical lens element. The image surface and the aperture stop are respectively at a front side and a rear side of the optical system. The first quarter-wave plate is between the image surface and the aperture stop. The partial reflector between the first quarter-wave plate and the aperture stop has an average light reflectivity of 35%. The second quarter-wave plate is between the partial reflector and the aperture stop. The reflective polarizer is between the second quarter-wave plate and the aperture stop. The first optical lens element between the image surface and the aperture stop has a convex front-side surface. The second optical lens element between the first optical lens element and the aperture stop has a concave rear-side surface.