Image Light Guide With Circular Polarizer for Stray-Light Control
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Solution Overview
Problem
Conventional image light guides face issues with environmental hazards such as dust and bright ambient conditions that degrade image quality, and scattered light can contaminate virtual images by re-entering the system, reducing contrast and clarity.
Innovation Solution
An optical imaging apparatus with a waveguide protected by an outer cover and a circular polarizer that blocks stray light from re-entering the waveguide, using a photochromic material to adjust to ambient light conditions and maintain image contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an outer cover is added to protect the waveguide from environmental hazards, then protection against dust and chemicals is improved, but stray light can reflect from the cover and re-enter the waveguide, reducing image contrast
Solution Approach 1:
A circular polarizer is introduced as an intermediary component between the waveguide and the outer cover. This polarizer blocks stray light reflected from the cover by utilizing polarization properties, allowing the cover to remain in place for environmental protection without suffering from stray light re-entry
Solution Approach 2:
The system changes the polarization state of light as it passes through the circular polarizer. By controlling the polarization parameter, the system allows useful light to pass while blocking reflected stray light that has its polarization altered by the reflective surface
2Manufacturing precision
If a polarizing filter is used to reduce rainbow phenomenon, then image quality is improved, but the system becomes sensitive to polarization states and requires additional optical components
Solution Approach 1:
The circular polarizer serves multiple functions simultaneously: it reduces the rainbow phenomenon by filtering polarized stray light, and it also blocks reflected stray light from the outer cover. This multi-functionality reduces the need for additional separate components
3Illumination intensity
If the waveguide is exposed to bright ambient conditions, then the field of view is maintained, but the contrast of virtual images is reduced
Solution Approach 1:
The circular polarizer acts as an intermediary that selectively transmits and blocks light based on its polarization state. It allows ambient light to pass through for maintaining field of view while blocking polarized stray light that would otherwise reduce image contrast
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 clearer virtual images by preventing stray light from re-entering the system, enhancing image quality and maintaining contrast in various environmental conditions.
Implementation Method 1
an in-coupling diffractive optic on one of the first and second surfaces... The in-coupling diffractive optic directs image-bearing light beams of a virtual image into the waveguide for propagation along the waveguide by internal reflections
Implementation Method 2
directs image-bearing light beams of a virtual image into the waveguide for propagation along the waveguide by internal reflections from the first and second surfaces
Implementation Method 3
an out-coupling diffractive optic on one of the first and second surfaces... The out-coupling diffractive optic directs the image-bearing light beams from the waveguide toward a viewer eyebox
Implementation Method 4
A circular polarizer interposed between waveguide and the outer cover blocks a return of stray light into the waveguide as a result of reflections of the stray light from the outer cover
Implementation Method 5
using a photochromic material to adjust to ambient light conditions and maintain image contrast
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
An imaging apparatus for conveying a virtual image superimposed within a view of an ambient environment has a waveguide having first and second surfaces. An in-coupling diffractive optic on one of the planar surfaces is disposed to direct image-bearing light beams into the waveguide. An out-coupling diffractive optic on one of the planar surfaces of the waveguide is disposed to direct the image-bearing light beams from the waveguide toward a viewer eyebox. An outer cover protects as least part of the waveguide from undesirable environmental influences of an ambient environment while supporting views of the ambient environment from the eyebox. A circular polarizer interposed between waveguide and the outer cover blocks the return of stray light into the waveguide.