Imaging Light Guide Reflective Turning Array
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Solution Overview
Problem
Conventional imaging light guides in head-mounted displays face inefficiencies due to optical losses at grating interfaces, limiting pupil expansion and brightness across the field of view, and are challenging to fabricate for 2-D beam expansion.
Innovation Solution
The use of a hybrid optical system combining diffractive optics for one-dimensional pupil expansion and reflective surfaces for two-dimensional expansion, with an array of partially reflective surfaces oriented in parallel to enhance optical efficiency and compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional diffractive optics (gratings) are used for pupil expansion, then pupil size can be increased, but optical losses occur at each grating interface reducing efficiency and brightness
Solution Approach 1:
The patent combines diffractive optics and reflective optics into a hybrid system. The reflective turning array mirrors work together with the diffractive in-coupling and out-coupling gratings to achieve pupil expansion while minimizing optical losses. The reflective surfaces have high reflectivity (>95%) compared to diffractive gratings, thereby reducing energy loss while maintaining pupil expansion capability.
Solution Approach 2:
The turning array is segmented into multiple discrete reflective surfaces (mirrors) arranged in an array configuration. Each mirror in the array reflects light beams at different angles, collectively achieving two-dimensional pupil expansion. This segmentation allows efficient light redirection with minimal losses compared to using extended diffractive structures.
2Area of stationary object
If multiple diffractive gratings are used for 2-D beam expansion, then pupil size increases, but fabrication complexity and alignment difficulty increase significantly
Solution Approach 1:
The turning array consists of multiple discrete reflective surfaces that can be independently fabricated and then assembled. Each mirror element is a simple reflective surface that is easier to manufacture than complex diffractive structures. The modular nature of the array allows for simplified fabrication processes and easier quality control compared to monolithic multi-grating systems.
Solution Approach 2:
The reflective turning array acts as an intermediary element between the in-coupling diffractive optic and the out-coupling diffractive optic. It simplifies the overall optical path by using simple reflection geometry rather than requiring complex multi-grating diffractive arrangements, thereby reducing fabrication and alignment complexity.
3Area of stationary object
If conventional diffractive turning optics are used, then pupil expansion is achieved, but optical efficiency decreases due to light energy loss at each interface
Solution Approach 1:
The hybrid optical system merges reflective turning surfaces with diffractive coupling optics. The reflective surfaces provide high-efficiency light redirection (>95% reflectivity) compared to diffractive turning gratings which scatter light and cause greater losses. This combination achieves pupil expansion while maintaining high optical efficiency and brightness.
Solution Approach 2:
The patent changes the optical parameter of the turning element from diffractive (grating-based) to reflective (mirror-based). This parameter change increases the reflectivity/efficiency of the turning operation from typical diffractive efficiency (60-80%) to high reflective efficiency (>95%), thereby improving overall optical efficiency while maintaining the pupil expansion function.
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 increases optical efficiency, brightness, and allows for more compact designs while providing image rotation and reversal, improving the presentation of high-resolution wide-field content in head-mounted displays.
Implementation Method 1
an in-coupling diffractive optic that directs a plurality of light beams, each representing a pixel of a virtual image, into the waveguide
Implementation Method 2
an array of two or more at least partially reflective surfaces oriented in parallel to each other that expands the image-bearing light beams from the in-coupling diffractive optic
Implementation Method 3
an out-coupling diffractive optic that expands the image-bearing light beams in a second dimension and directs the image-bearing light beams from the waveguide toward a viewer eyebox
Data Source
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AI summary
An imaging light guide has a waveguide and an in-coupling diffractive optic formed on the waveguide and disposed to direct image-bearing light beams into the waveguide. An array of two or more at least partially reflective surfaces are oriented in parallel and disposed to expand the image-bearing light beams from the in-coupling diffractive optic in a first dimension and to direct the expanded image-bearing light beams toward an out-coupling diffractive optic. The out-coupling diffractive optic is formed on the waveguide and disposed to expand the image-bearing light beams in a second dimension orthogonal to the first dimension and to direct the image-bearing light beams toward a viewer eyebox.