Head-Mounted Optical Layout With Folded Path and Stray Light Control
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Solution Overview
Problem
Existing head-mounted devices face challenges in achieving a balance between reducing size and weight while maintaining high image quality, as conventional optical lenses provide good image quality but are bulky, and Fresnel lenses compromise image quality for size reduction.
Innovation Solution
An optical system comprising an aperture stop, reflective polarizer, partial reflector, quarter-wave plates, and lens elements with specific refractive powers and curvature ratios, arranged to form a catadioptric system that reduces total track length and eliminates stray light, enhancing image quality and minimizing device size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
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, second, and third optical lens elements) with different refractive powers. Each lens element contributes to correcting specific aberrations, allowing the system to maintain high image quality while reducing the overall track length compared to a single conventional lens.
Solution Approach 2:
The patent introduces a catadioptric design that combines refractive elements with reflective components (reflective polarizer, partial reflector, quarter-wave plates). This adds the dimension of reflection to the traditionally refractive optical path, folding the light path and reducing the axial length of the system while maintaining imaging quality.
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 uses a composite design combining multiple lens elements with different materials and optical properties. The first lens element has negative refractive power while the third has positive refractive power, creating a composite optical system that corrects aberrations and maintains image quality without requiring Fresnel lens structures.
Solution Approach 2:
The patent carefully controls the refractive powers and curvature radii of each lens element. By adjusting these parameters (the third lens element's curvature radii satisfying a specific relationship), the system achieves compact size while correcting off-axis aberrations that would otherwise degrade image quality.
3Length of stationary object
If the optical path is folded to reduce size, then device dimensions are reduced, but stray light increases
Solution Approach 1:
The reflective polarizer and partial reflector act as intermediary components that carefully control the reflection and transmission of light. These components are positioned and designed to fold the optical path while minimizing stray light generation through proper coating and angular design.
Solution Approach 2:
The quarter-wave plates are strategically placed to convert potentially harmful stray light into useful imaging light by manipulating polarization states. The reflected light that might otherwise become stray light is converted into properly polarized light that contributes to the image formation.
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 system achieves high image quality with reduced size and weight by folding the optical path through polarization and reflection, utilizing aspheric lens surfaces and materials like glass or plastic to optimize refractive power and minimize aberrations.
Implementation Method 1
a reflective polarizer, located between the aperture stop and the image display surface
Implementation Method 2
a reflective polarizer, located between the aperture stop and the image display surface
Implementation Method 3
a first quarter-wave plate, located between the reflective polarizer and the partial reflector; a second quarter-wave plate, located between the partial reflector and the image display surface
Implementation Method 4
a first optical lens element, located between the aperture stop and the image display surface; a second optical lens element, located between the first optical lens element and the image display surface; a third optical lens element, located between the second optical lens element and the image display surface
Data Source
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AI summary
An optical system (1) includes an aperture stop (ST), an image display surface (IMG), a reflective polarizer (RP), a partial reflector (BS), first and second quarter-wave plates (QWP1, and QWP2), and first, second and third optical lens elements (E1, E2, and E3). The aperture stop (ST) and the image display surface (IMG) are respectively at front side and rear side of the optical system (1). The reflective polarizer (RP) is between the aperture stop (ST) and the image display surface (IMG). The partial reflector (BS) is between the reflective polarizer (RP) and the image display surface (IMG). The first quarter-wave plate (QWP1) is between the reflective polarizer (RP) and the partial reflector (BS). The second quarter-wave plate (QWP2) is between the partial reflector (BS) and the image display surface (IMG). The first, second and third optical lens elements (E1, E2, and E3) are between the aperture stop (ST) and the image display surface (IMG) in order from the front side to the rear side. The first optical lens element (E1) has negative refractive power. The second optical lens element (E2) has planar front-side surface.