Imaging Light Guide Reflective Turning Array
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Solution Overview
Problem
Conventional imaging light guides in head-mounted displays suffer from optical losses at grating interfaces, limiting efficiency and requiring bright input image sources to compensate for lost brightness, and are challenging to fabricate for 2-D beam expansion due to complex alignment requirements.
Innovation Solution
The use of a planar waveguide with an in-coupling diffractive optic, an array of partially reflective surfaces, and an out-coupling diffractive optic for pupil expansion, allowing for improved optical efficiency and compact design by redirecting light through reflection within the waveguide, rather than relying solely on diffraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional diffractive optics (gratings) are used for light coupling and pupil expansion, then the device achieves compact size and reduced weight, but optical efficiency is limited due to losses at each grating interface
Solution Approach 1:
The optical system is segmented into distinct functional zones: input coupling region with diffractive optics, intermediate transport region with reflective surfaces for pupil expansion, and output coupling region. This segmentation allows each region to be optimized for its specific function, reducing overall optical losses while maintaining compact form factor.
Solution Approach 2:
Reflective surfaces are introduced as intermediary elements between the input and output diffractive optics. These intermediaries redirect and expand the light beam using reflection rather than diffraction, thereby avoiding the efficiency losses associated with additional grating interfaces while still achieving the required pupil expansion.
2Ease of operation
If multiple diffractive optics are used for 2-D pupil expansion, then the desired pupil expansion is achieved, but manufacturing complexity increases due to alignment requirements
Solution Approach 1:
Multiple pupil expansion functions are merged into a single intermediate reflective surface structure. Instead of requiring separate diffractive optics for each expansion dimension, the reflective surfaces are arranged to provide both horizontal and vertical beam expansion through a unified geometric configuration, simplifying manufacturing and alignment.
Solution Approach 2:
The patent replaces diffractive optical mechanisms with geometric reflection-based mechanisms for pupil expansion. This substitution eliminates the need for precise diffraction pattern alignment while maintaining the ability to achieve 2-D pupil expansion through controlled light reflection paths.
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 solution enhances brightness and efficiency while providing a compact, high-resolution wide field of view for the viewer, allowing for more flexible display design and reducing the need for complex alignment in manufacturing.
Implementation Method 1
collimated, relatively angularly encoded light beams from an image source are coupled into a planar waveguide by an input coupling such as an in-coupling diffractive optic
Implementation Method 2
redirecting light through reflection within the waveguide
Implementation Method 3
the diffracted light can be directed back out of the waveguide by a similar output grating
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.