Angle-Selective LC Dimming Element for AR Rainbow Suppression
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Solution Overview
Problem
Augmented Reality (AR) headsets with pupil-expansion waveguide displays experience a 'rainbow effect' due to diffractive structures, which degrades the see-through view quality, especially when users encounter bright light sources from certain angles, and conventional dimming methods often reduce the brightness of the desired see-through image.
Innovation Solution
An optical device with a liquid crystal (LC) dimming element that attenuates light intensity based on incidence angle, combined with a linear polarizer to convert light and a tunable dimming element to adjust brightness, effectively reducing the rainbow effect while maintaining image brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional dimming elements are used to dim light at different incidence angles, then the rainbow effect is suppressed, but the brightness of the desired see-through image is reduced
Solution Approach 1:
The liquid crystal dimming element is configured with spatially varying properties where different regions have different light attenuation characteristics. Specifically, the element attenuates light more strongly at high incidence angles (suppressing rainbow) while maintaining higher transmittance at low incidence angles (preserving see-through image brightness), creating local quality variations to resolve the contradiction.
Solution Approach 2:
The liquid crystal dimming element changes its optical parameters (light attenuation coefficient) based on the incidence angle of incoming light. By adjusting the liquid crystal orientation and optical properties dynamically or spatially, the element achieves angle-dependent light control, allowing strong attenuation for rainbow suppression at high angles while maintaining brightness for see-through imaging at low angles.
2Object-affected harmful factors
If a polarizing film is used to dim undesired rainbow, then the polarization sensitive grating works, but the brightness of the desired see-through image is reduced due to only 40% light transmission
Solution Approach 1:
The liquid crystal dimming element provides localized light control with different attenuation properties for different light paths. It selectively attenuates polarized light from the rainbow effect while allowing sufficient transmission of unpolarized or differently polarized light from the see-through image, achieving local quality differentiation to resolve the brightness loss issue.
Solution Approach 2:
The solution uses a composite optical system combining liquid crystal material with specific optical properties rather than a simple polarizing film. This composite approach allows simultaneous control of polarization-dependent attenuation for rainbow suppression and overall light transmission for image brightness, overcoming the 40% transmission limitation of conventional polarizing films.
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 significantly reduces the rainbow effect caused by diffractive structures in AR headsets by attenuating light at high incidence angles, preserving the brightness of the see-through image, thereby enhancing the overall image quality.
Implementation Method 1
The dimming element includes a liquid crystal (LC) dimming element that enhances an attenuation of the light as the incidence angle increases
Implementation Method 2
attenuating, by the dimming element, an intensity of the light with an incidence angle
Implementation Method 3
converting, by a linear polarizer, the light from the real world to a linear polarized light
Data Source
AI summary
A method to suppress a rainbow effect and an optical device thereof are provided. The method includes receiving, by a dimming element, a light from a real world. The method further includes attenuating, by the dimming element, an intensity of the light with a degree of attenuation growing with an incidence angle. The dimming element includes a liquid crystal (LC) dimming element.