See-through Display Stray Light Management
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Solution Overview
Problem
Head-mounted displays (HMDs) that provide a see-through view are affected by stray light, which reduces image sharpness and contrast, and causes black areas to appear gray, compromising the see-through view by combining environmental light with displayed light.
Innovation Solution
The implementation of optical configurations and light management systems within the HMDs, including polarized light sources, reflective polarizers, TIR wedges, and dark light traps, to minimize stray light and enhance contrast by directing 'off' pixel light away from the optical axis, allowing only 'on' pixel light to reach the user's eye.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If see-through display combines environmental light with displayed light, then visibility of environment is maintained, but image contrast deteriorates because black areas appear gray
Solution Approach 1:
The optical system is segmented into distinct functional zones: a first optical element that transmits environmental light to the user's eye, and a second optical element that reflects displayed light to the user's eye. This segmentation allows the system to separate the paths of environmental light and displayed light, enabling the displayed image to be superimposed on the environmental view while maintaining image contrast by preventing stray light from degrading the black areas of the displayed image.
2Measurement precision
If stray light is present in the optical system, then light reaches the user's eye from multiple paths, but image sharpness deteriorates
Solution Approach 1:
The patent extracts and eliminates stray light from the optical system by using a light trap positioned to capture light that scatters or reflects from optical surfaces. The light trap selectively removes stray light paths while preserving the intended optical paths for both environmental light transmission and displayed light reflection, thereby maintaining image sharpness without compromising the see-through functionality.
3Illumination intensity
If polarized light sources and reflective polarizers are used, then stray light is reduced and contrast is enhanced, but device complexity increases
Solution Approach 1:
The first optical element is designed to perform multiple functions: it transmits environmental light to the user's eye and also serves as a support structure for the polarized light source and reflective polarizer assembly. The second optical element similarly functions as both a reflector for displayed light and a structural component. This multi-functionality reduces the need for additional separate components, thereby managing device complexity while achieving stray light reduction and contrast enhancement through polarized light management.
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 improves image contrast and sharpness by reducing stray light, enabling deeper blacks and higher brightness in see-through displays, providing a clearer and more immersive augmented reality experience.
Implementation Method 1
including polarized light sources, reflective polarizers
Implementation Method 2
TIR wedges
Implementation Method 3
dark light traps, to minimize stray light
Data Source
AI summary
Aspects of the present invention relate to providing see-through computer display optics.