Folded Prism HMD Optics for Large FOV in Thin AR Displays
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Solution Overview
Problem
Current AR solutions struggle to achieve a large field of view (FOV) while maintaining a lightweight and thin form factor, often resulting in poor imaging quality and color cast issues.
Innovation Solution
A lightweight head-mounted display apparatus with a large FOV is designed using a foldable optical path that incorporates a first and second imaging prism unit, a first imaging lens unit, and a polarization conversion unit, employing principles of reflection, refraction, and polarization to achieve multiple optical path foldings, ensuring imaging quality and diopter adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If an optical waveguide solution is used to achieve lightening and thinning, then the thickness is reduced, but the imaging effect and field of view become insufficient
Solution Approach 1:
The patent transforms the optical path from a straight linear arrangement to a folded multi-dimensional configuration using prisms and reflective films. The light path is bent multiple times within the compact optical module, allowing the field of view to expand in angular space while the physical thickness remains small. This dimensional transformation of the optical path enables simultaneous achievement of thin profile and large FOV.
Solution Approach 2:
The optical components are nested within each other in a compact arrangement. The optical module embeds multiple functional elements (prisms, reflective films, lens arrays) in a layered nested structure, where each component is positioned within the space defined by the previous component. This nested configuration maximizes the utilization of the limited thickness space while maintaining the complex folded optical path needed for large FOV.
2Area of stationary object
If the structural size is increased to achieve a large field of view, then the field of view is improved, but the device becomes heavier and thicker
Solution Approach 1:
Instead of increasing the physical size linearly to expand FOV, the patent uses optical folding to redirect light paths in multiple dimensions. The prisms and reflective films create a three-dimensional optical path that folds back on itself, allowing the effective optical aperture to be large while the physical housing remains compact and thin.
Solution Approach 2:
The patent replaces a mechanically large optical system with a compact optical system that uses reflective and refractive principles. Instead of using a large physical lens or mirror to achieve wide FOV, the system uses multiple reflections and refractions through prisms and films to achieve the same angular coverage in a much smaller physical footprint.
3Manufacturing precision
If a Birdbath solution is used to provide good image quality, then the imaging effect is improved, but the thickness increases to 18-20 mm which cannot meet daily wearing requirements
Solution Approach 1:
The patent folds the optical path into a compact three-dimensional configuration using prisms and reflective films, reducing the linear thickness from 18-20 mm to under 10 mm while preserving the imaging quality. The folded optical path maintains the necessary optical component spacing and alignment for high-quality imaging within a thinner profile.
Solution Approach 2:
The optical components are arranged in a nested configuration where the optical path folds within itself, allowing the imaging system to be compressed into a thinner form factor. The lens arrays, prisms, and reflective films are positioned in nested layers that maintain the precise optical relationships needed for high-quality imaging while reducing overall thickness.
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 apparatus achieves a FOV increase from 48° to 60° or above, reducing thickness by half, while ensuring imaging quality and providing diopter adjustment, thus addressing the challenges of lightening and thinning.
Implementation Method 1
A linear polarization film is disposed on a light-emitting side of the display image source. Imaging light emitted by the display image source is converted by the linear polarization film into linear polarization light
Implementation Method 2
the linear polarization light enters the first imaging prism unit and undergoes total reflection
Implementation Method 3
arrives at the film unit, and is reflected by the film unit to the first imaging lens unit
Implementation Method 4
arrives at the first imaging lens unit, and then is reflected back to the first imaging prism unit by the first imaging lens unit
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A lightweight head-mounted display apparatus with a large field of view includes: a display image source (1), provided with a linear polarization film on a light-emitting side; a first imaging prism unit (2), including a film unit and a first prism, where the film unit includes a polarization reflection unit and is attached to a side, away from a first imaging lens unit (4), of the first prism; a second imaging prism unit (3), including a second prism and being disposed near the film unit; the first imaging lens unit (4), attached with a transflective film on a side away from the first imaging prism unit (2); and a polarization conversion unit, located between the first imaging prism unit (2) and the first imaging lens unit (4), or located between the polarization reflection unit and the second imaging prism unit (3). Thicknesses of the linear polarization film, the film unit, the polarization conversion unit, and the transflective film are properly set. The head-mounted display apparatus achieves lightening and thinning while increasing a field of view, thereby ensuring imaging quality and providing a diopter adjustment function.