Curved Lightguide with Gradient Index for Wide Field of View
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Solution Overview
Problem
Conventional planar lightguides in AR/VR display systems face challenges in providing a wide field of view due to their geometry mismatch with the spherical shape of the human eye, leading to increased complexity in design and manufacture, and require varying extraction elements to maintain image quality across the field of view.
Innovation Solution
The use of curved lightguides with a gradient index of refraction that decreases as the radial distance from the center of curvature increases, allowing for a wider field of view while maintaining consistent ray angles through total internal reflection, using either spherical or cylindrical symmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a planar lightguide is used to provide a wide field of view, then the field of view increases, but the design and manufacture complexity increases due to the geometry mismatch with the spherical eye
Solution Approach 1:
The patent applies spheroidality by transitioning from a planar lightguide to a curved lightguide that matches the spherical geometry of the human eye. The curved lightguide has a radius of curvature that corresponds to the eye's pupil rotation radius, allowing the eye to rotate about the lightguide's center of curvature while maintaining a constant distance. This geometric matching eliminates the need for complex variable extraction elements and simplifies both design and manufacture while providing a wide field of view.
2Adaptability or versatility
If a planar lightguide is used to provide a wide field of view, then the field of view increases, but irregularly shaped extraction elements are required to maintain image quality
Solution Approach 1:
The curved lightguide geometry ensures that light rays exit at consistent angles across the field of view, allowing the use of regular, uniformly spaced extraction elements with simple geometric shapes. This eliminates the manufacturing complexity associated with creating irregularly shaped extraction elements while maintaining image quality across the entire wide field of view.
3Adaptability or versatility
If the distance from the pupil to the lightguide changes as the eye rotates, then the field of view increases, but the system complexity increases
Solution Approach 1:
The curved lightguide is positioned such that the eye's pupil rotates about the lightguide's center of curvature. This geometric arrangement ensures that the distance from the pupil to the lightguide remains constant throughout the entire field of view, eliminating the need for complex adaptive mechanisms. The constant distance simplifies the optical system design and maintains consistent image quality across all viewing angles.
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
This approach enables a fixed distance between the eye and the lightguide as the eye rotates, reducing the complexity of design and manufacture, and allows for a wider field of view without the need for irregular extraction elements, improving image quality and diffraction efficiency.
Implementation Method 1
The outer surfaces provide total internal reflection to guide light within the lightguide
Implementation Method 2
The transmission medium has a gradient index of refraction that decreases as function of increasing distance from the point
Implementation Method 3
Diffraction techniques use extraction features smaller than or approximately equal to the operative wavelength(s) of light to redirect (i.e., diffract) light of selected wavelengths toward an eye
Data Source
AI summary
A lightguide comprised of a transmission medium having a first curved outer surface and a second curved outer surface and in at least one cross-section of the lightguide. The first curved outer surface and the second curved outer surface are substantially concentric around a point. The transmission medium having a gradient index of refraction that decreases as function of increasing distance from the point, the gradient index extending from the first curved surface to the second curved surface. At least one light extraction element disposed to extract light from the transmission medium and direct the light generally toward the point. Both the lightguide and the gradient index profiles may be spherical or cylindrical.