Curved Waveguide Exit Pupil Expansion
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Solution Overview
Problem
Near-eye display devices with small exit pupils struggle to accommodate varying interpupillary distances and pupil positions, leading to vignetting and limited field of view, especially when trying to combine virtual imagery with real-world backgrounds in augmented reality applications.
Innovation Solution
A curved waveguide with varying curvature along the optical path is used to expand the exit pupil by replicating it in one dimension through pupil replication and in another dimension through its shape, allowing different field of view portions to be positioned at the same location, thereby enhancing the eyebox and field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a waveguide is used to deliver images to the user's eye, then the device can provide virtual imagery with real-world background, but the exit pupil remains small causing vignetting and limited field of view
Solution Approach 1:
The patent transitions from a flat waveguide to a curved waveguide geometry, adding spatial curvature as a new dimension. This curvature allows light rays to be redirected and expanded in the exit pupil direction without increasing the physical footprint of the device, thereby resolving the contradiction between maintaining compact form factor and expanding exit pupil size for better adaptability to varying interpupillary distances
Solution Approach 2:
The waveguide is given a curved cross-sectional geometry rather than a flat profile. This curvature is specifically designed to expand the exit pupil by manipulating the optical path of light rays as they propagate through the waveguide, allowing the system to accommodate varying interpupillary distances while maintaining a compact device form factor
2Area of stationary object
If the waveguide is made compact, then the device is aesthetically pleasing and wearable, but the field of view and eyebox are limited
Solution Approach 1:
The patent utilizes the curvature dimension of the waveguide to expand the eyebox area without proportionally increasing the overall device length. By bending the waveguide in a curved configuration, the optical path is extended in a compact spatial envelope, effectively increasing the eyebox size while maintaining wearable form factors
3Area of stationary object
If variable pitch gratings are used, then the exit pupil can be increased, but the manufacturing complexity increases
Solution Approach 1:
The patent implements variable pitch gratings where the grating period changes locally across different regions of the waveguide. This local variation in grating parameters is specifically tailored to the curved waveguide geometry to achieve uniform exit pupil expansion, balancing the manufacturing complexity with the optical performance benefits
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 a larger eyebox and wider field of view, preventing vignetting and allowing users with different interpupillary distances to view the entire field of view without losing imagery as they move their eyes, while maintaining a compact and aesthetically pleasing design.
Implementation Method 1
an input grating coupled to or within the waveguide to diffract said image bearing light to propagate internally along the curved waveguide by total internal reflection
Implementation Method 2
an output grating provided along a side of the waveguide by which the image bearing light is diffracted out of the waveguide for viewing by the viewer
Data Source
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AI summary
Examples are disclosed that relate to expanding an exit pupil of a display device via a curved waveguide. One example provides a curved waveguide, including an input coupler configured to couple light into the curved waveguide, a first reflective surface, a second reflective surface opposing the first reflective surface, and an output coupler configured to couple the light out of the curved waveguide. The curved waveguide also has a curvature in a direction transverse to an optical path between the input coupler and the output coupler, the curvature having a radius that varies along a direction extending between the input coupler and the output coupler.