Folded Optical Layout for Compact Head-Mounted Imaging
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Solution Overview
Problem
Conventional optical lenses in head-mounted devices struggle to balance size reduction with high image quality, while Fresnel lenses compromise image quality for reduced size.
Innovation Solution
An optical system comprising an aperture stop, reflective polarizer, partial reflector, quarter-wave plates, and multiple lens elements with specific refractive powers and arrangements to fold light paths and reduce stray light, combined with anti-reflection layers and aspheric lens surfaces to enhance image quality and compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional optical lenses are used, then image quality is good, but device size cannot be effectively reduced
Solution Approach 1:
The optical system is divided into multiple lens elements (first optical lens element, second optical lens element, third optical lens element) with different refractive powers. Each lens element is optimized for specific functions: the first lens element has positive refractive power for light convergence, the second lens element has negative refractive power for divergence control, and the third lens element has negative refractive power for additional focusing adjustment. This segmentation allows each component to be miniaturized while collectively achieving high image quality.
Solution Approach 2:
The patent introduces a reflective polarizer and partial reflector that fold the light path in a multi-dimensional arrangement. The reflective polarizer is located between the aperture stop and the image surface, while the partial reflector is positioned between the reflective polarizer and the image surface. This creates a compact folded optical path that reduces the overall device volume while maintaining image quality through precise light path control.
2Volume of moving object
If Fresnel lenses are used, then device size is reduced, but image quality becomes poor
Solution Approach 1:
The optical system combines multiple lens elements with different refractive properties and a reflective polarizer in a composite configuration. The first optical lens element has positive refractive power, while the second and third optical lens elements have negative refractive power. This composite structure integrates the advantages of both refractive and reflective optical elements to achieve compact size without sacrificing image quality.
Solution Approach 2:
The reflective polarizer and partial reflector create a folded light path that extends in multiple dimensions rather than a single linear path. This multi-dimensional light path folding allows the optical system to achieve a compact device volume while maintaining sufficient optical length for high-quality image formation.
3Manufacturing precision
If multiple lens elements are added to improve image quality, then device complexity increases
Solution Approach 1:
The patent merges the functions of multiple optical elements into a compact integrated structure. The first optical lens element, second optical lens element, and third optical lens element are positioned in sequence with specific spacing, and the reflective polarizer and partial reflector are integrated into the light path. This merging approach reduces device complexity by optimizing the arrangement and spacing of elements rather than simply adding more components.
Solution Approach 2:
Each lens element is designed with specific local optical properties: the first optical lens element has positive refractive power for light convergence, the second optical lens element has negative refractive power for divergence control, and the third optical lens element has negative refractive power for additional focusing adjustment. The reflective polarizer and partial reflector are positioned at specific locations to control light paths locally. This localized optimization reduces overall system complexity while achieving 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
The solution achieves a compact head-mounted device with improved image quality by reducing total track length, eliminating stray light, and optimizing lens configurations for efficient imaging.
Implementation Method 1
a first optical lens element with positive refractive power
Implementation Method 2
a second optical lens element with negative refractive power
Implementation Method 3
a third optical lens element with negative refractive power
Implementation Method 4
a reflective polarizer
Implementation Method 5
a partial reflector
Implementation Method 6
a first quarter-wave plate
Implementation Method 7
a second quarter-wave plate
Data Source
AI summary
An optical system includes an aperture stop, an image surface, a reflective polarizer, a partial reflector, first and second quarter-wave plates and first, second and third lens elements. The aperture stop and the image surface are respectively at a front side and a rear side of the optical system. The reflective polarizer is between the aperture stop and the image surface. The partial reflector is between the reflective polarizer and the image surface. The first quarter-wave plate is between the reflective polarizer and the partial reflector. The second quarter-wave plate is between the partial reflector and the image surface. The first lens element is between the aperture stop and the image surface. The second lens element is between the first lens element and the image surface. The third lens element has negative refractive power and is between the second lens element and the image surface.