Curved Lenslet Arrays for Wide-FOV, Large-Eyebox Head-Mounted Imaging
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Solution Overview
Problem
Conventional HMD designs face challenges in achieving a wide field of view, large output pupil size, and high resolution while maintaining a compact geometry, which is essential for wearability and cost-effectiveness, especially in augmented reality applications.
Innovation Solution
A head-mounted imaging apparatus utilizing a projector, a curved mirror, a lenslet array, and a beamsplitter to form a virtual image, with the lenslet array positioned at one focal length from the curved mirror, expanding the beam width and forming a virtual image that allows for a large eye box and minimal optical adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional optics are used to achieve wide field of view and large output pupil size, then the field of view and pupil size can be improved, but the system becomes bulky, complex, and costly
Solution Approach 1:
The patent divides the optical system into distinct functional modules: a ball lens for image formation, a beam expander for pupil size control, and a collimating mirror for wide field of view. This segmentation allows each component to be optimized independently, achieving wide FOV and large pupil size without requiring a single complex optical system.
Solution Approach 2:
The patent employs a nested optical configuration where the beam expander is positioned within the optical path between the ball lens and the collimating mirror. This nesting allows compact arrangement of multiple optical functions in a space-efficient manner, reducing overall system complexity while maintaining performance.
2Area of stationary object
If ball lenses are used at high diverging angles to achieve large output pupils in compact HMDs, then the output pupil size can be improved, but spherical aberration increases and degrades image resolution
Solution Approach 1:
The patent introduces a beam expander that dynamically adjusts the beam divergence angle before light reaches the ball lens. By controlling the divergence angle to be lower than it would be in conventional compact HMD designs, the system achieves large output pupil size while maintaining acceptable image resolution by reducing spherical aberration.
Solution Approach 2:
The beam expander acts as an intermediary element between the light source and the ball lens, modifying the beam characteristics before they reach the lens. This intermediary component enables the system to achieve large output pupils without subjecting the ball lens to high diverging angles that would cause spherical aberration.
3Device complexity
If the image is projected by symmetric ball lens optics in the path between the observer and collimating mirror, then the optical path can be simplified, but additional beam expanding elements cannot be used
Solution Approach 1:
The patent repositions the ball lens to form the image in a different spatial location within the optical path, specifically placing it before the collimating mirror rather than between the mirror and observer. This dimensional repositioning creates available optical space for inserting beam expanding elements without complicating the overall optical path.
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 provides an enlarged pupil size with high-resolution wide field of view content, suitable for a range of intraocular distances, while maintaining a compact form factor and enabling augmented reality by allowing partial ambient environment visibility.
Implementation Method 1
a lenslet array positioned adjacent to the real image plane and optically disposed at substantially one focal length away from the curved mirror, wherein the lenslet array is curved about a single axis
Implementation Method 2
a curved mirror that is partially transmissive to allow at least partial visibility of the ambient environment to one eye of an observer, wherein a surface of the curved mirror is substantially spherical
Implementation Method 3
a beamsplitter in a path of light from the real image at the lenslet array and disposed to direct at least a portion of the light from the real image toward the curved mirror
Implementation Method 4
a projector that is energizable to project image-bearing light
Data Source
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AI summary
A head-mounted imaging apparatus has a projector that is energizable to project image-bearing light and a light-conditioning element that directs and shapes the image-bearing light from the projector to form a real image plane. A lenslet array is positioned adjacent to the real image plane and optically disposed at substantially one focal length away from a curved mirror, wherein the surface of the curved mirror is substantially spherical. There is a beamsplitter in the path of light from the real image at the lenslet array and disposed to direct at least a portion of the light from the real image toward the curved mirror. The curved mirror directs light from the beamsplitter to form a virtual image for an observer who wears the head-mounted imaging apparatus.