Folded Optical Lens Assembly for Lighter AR Image Quality
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Solution Overview
Problem
Current head-mounted displays are weight-heavy and have poor image quality.
Innovation Solution
An optical lens assembly with a folded light path design, comprising specific lenses with refractive power and optical elements, including absorptive and reflective polarizers, phase retarders, and a partial-reflective-partial-transmissive element, optimized by conditions such as focal lengths, radii of curvature, and material properties to reduce weight and enhance image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If a conventional head-mounted display design is used, then the device can display images, but the device becomes weight-heavy
Solution Approach 1:
The optical system is divided into multiple discrete lens elements (first lens, second lens, third lens) with specific refractive powers and surface curvatures. Each lens element is optimized independently with specific parameters (e.g., R1, R2, CT1, CT2) to reduce overall weight while maintaining collective imaging performance.
Solution Approach 2:
The patent introduces a folded light path configuration where the optical axis bends at the partial-reflective-partial-transmissive element. This dimensional change in light propagation allows compact arrangement of optical elements, reducing the overall device volume and weight while preserving image quality through careful control of focal lengths and element positions.
2Weight of moving object
If the optical path is folded to reduce weight, then the device weight decreases, but the image quality may deteriorate
Solution Approach 1:
The patent specifies precise parameter ranges for each lens element including focal lengths (f1, f2, f3), radii of curvature (R1, R2, R3, R4), and central thicknesses (CT1, CT2, CT3). These parameter optimizations ensure that the folded light path configuration maintains high image quality by controlling aberrations and focal properties despite the compact arrangement.
Solution Approach 2:
The optical system combines multiple lens materials with different refractive indices and Abbe numbers. The first lens has positive refractive power with specific dispersion properties, while the second and third lenses have negative refractive powers with complementary optical characteristics. This composite material approach balances chromatic and spherical aberrations in the folded configuration.
3Manufacturing precision
If multiple optical elements are added to improve image quality, then the image quality improves, but the device complexity increases
Solution Approach 1:
Each lens element serves multiple functions: the first lens with positive power provides primary convergence, while also contributing to chromatic correction. The second and third lenses with negative powers simultaneously diverge light and correct spherical aberration. The partial-reflective-partial-transmissive element serves as both a beam splitter and a folding mirror. This multi-functionality reduces the need for additional dedicated correction elements.
Solution Approach 2:
The patent employs aspheric surfaces on lens elements, defined by conic constants and higher-order coefficients (A4, A6, A8, A10). These curved surface profiles enable single elements to perform multiple correction functions that would otherwise require separate spherical elements, thereby reducing 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
The design achieves a lighter head-mounted device with improved image quality and a larger angle of view while maintaining illuminance, reducing aberrations and assembly sensitivity.
Implementation Method 1
a first lens with positive refractive power, including a visual-side surface, and the visual-side surface of the first lens being convex in a paraxial region thereof
Implementation Method 2
a partial-reflective-partial-transmissive element
Implementation Method 3
an optical element including, in order from the visual side to the image source side, an absorptive polarizer, a reflective polarizer
Implementation Method 4
a first phase retarder; a second phase retarder
Implementation Method 5
a second lens with positive refractive power, including a visual-side surface and an image source-side surface, the image source-side surface of the second lens being convex in a paraxial region thereof, and at least one of the visual-side surface and the image source-side surface of the second lens being aspheric
Data Source
AI summary
An optical lens assembly includes, in order from a visual side to an image source side: a first lens with positive refractive power; an optical element including, in order from the visual side to the image source side, an absorptive polarizer, a reflective polarizer and a first phase retarder; a second lens with positive refractive power; a partial-reflective-partial-transmissive element; a second phase retarder; and an image source plane. The optical lens assembly has a total of two lenses with refractive power. A focal length of the optical lens assembly is f, a maximum image-source height of the optical lens assembly is INM, a focal length of the first lens is f1, a focal length of the second lens is f2, and following conditions are satisfied: 0.40<IMH/f<1.26 and 0.21<f2/f1<2.35. A head-mounted electronic device includes the optical lens assembly.