Folded-Path Optical System for Compact Head-Mounted Displays
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Solution Overview
Problem
Conventional optical lenses in head-mounted devices struggle to balance size reduction with high image quality, with Fresnel lenses compromising image quality while conventional lenses fail to minimize device size effectively.
Innovation Solution
An optical system comprising an aperture stop, reflective polarizer, partial reflector, quarter-wave plates, and multiple lens elements, including one with negative refractive power, arranged to fold light paths and reduce stray light, combined with aspheric lens surfaces and anti-reflection layers to enhance image quality and minimize device size.
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 and characteristics. 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 positive refractive power for final focusing. This segmentation allows each element to be optimized independently while working together to achieve both compact size and high image quality.
Solution Approach 2:
The optical system employs a composite lens structure combining multiple lens elements with different material properties and refractive indices. The lens elements are designed with specific curvature radii and thicknesses to create a composite optical system that achieves aberration correction and compact sizing. The combination of lenses with different characteristics (convex and concave surfaces) creates a synergistic effect that neither single lens could achieve alone.
2Volume of moving object
If Fresnel lenses are used, then device size is reduced, but image quality becomes poor
Solution Approach 1:
Instead of using a single Fresnel lens, the system segments the optical function across multiple conventional lens elements. Each lens element is designed with specific refractive powers and optical characteristics that collectively achieve the compact sizing goal while maintaining high image quality through proper aberration correction.
Solution Approach 2:
The system changes the optical parameters by using multiple lens elements with specific refractive powers (positive and negative combinations) and curvature radii. The first lens element has positive refractive power with specific curvature, the second has negative refractive power, and the third has positive refractive power. This parameter optimization allows the system to achieve compact size without sacrificing image quality, avoiding the need for Fresnel lens structures.
3Manufacturing precision
If multiple lens elements are added to improve image quality, then aberration correction is enhanced, but device complexity increases
Solution Approach 1:
Each lens element is designed with specific local optical characteristics optimized for its position and function in the system. The first lens element has specific curvature radii (R1, R2) and thickness (d1) optimized for its role in light convergence, the second lens element has curvature radii (R3, R4) and thickness (d2) optimized for divergence control, and the third lens element has curvature radii (R5, R6) and thickness (d3) optimized for final focusing. This localized optimization allows the system to achieve high image quality while keeping each individual element relatively simple.
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 reduced device size and weight while maintaining high image quality by folding light paths and correcting aberrations, enabling improved performance in head-mounted devices.
Implementation Method 1
a reflective polarizer located between the aperture stop and the image surface
Implementation Method 2
a first quarter-wave plate located between the reflective polarizer and the partial reflector, a second quarter-wave plate
Implementation Method 3
a first optical lens element located between the aperture stop and the image surface, a second optical lens element located between the first optical lens element and the image surface, and a third optical lens element located between the second optical lens element and the image surface
Implementation Method 4
a partial reflector located between the reflective polarizer and the image surface
Data Source
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AI summary
An optical system (1) includes an aperture stop (ST), an image surface (IMG), a reflective polarizer (RP), a partial reflector (BS), first and second quarter-wave plates (QWP1 and QWP2) and first, second and third lens elements (E1, E2 and E3). The aperture stop (ST) and the image surface (IMG) are respectively at a front side and a rear side of the optical system (1). The reflective polarizer (RP) is between the aperture stop (ST) and the image surface (IMG). The partial reflector (BS) is between the reflective polarizer (RP) and the image 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 surface (IMG). The first lens element (E1) is between the aperture stop (ST) and the image surface (IMG). The second lens element (E2) is between the first lens element (E1) and the image surface (IMG). The third lens element (E3) has negative refractive power and is between the second lens element (E2) and the image surface (IMG).