See-through Display Stray Light Management
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Solution Overview
Problem
Head-mounted displays (HMDs) with see-through capabilities suffer from stray light issues, which reduce image sharpness and contrast by causing black areas to appear gray, affecting both the displayed image and the see-through view of the environment.
Innovation Solution
The implementation of an optical system that includes a DLP-based upper optical module with a polarized light source, reflective polarizer, and a quarter-wave retarder film, along with a light trap to manage stray light by directing dark state light away from the optical axis, ensuring that only 'on' pixels contribute to the image perceived by the user.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a see-through optical system is used to provide environmental view, then transparency and see-through capability are improved, but stray light from the environment enters the optical path and reduces image contrast and sharpness
Solution Approach 1:
The patent extracts and removes stray light from the optical path using dedicated light trapping structures. The light trap is positioned to intercept dark state light that would otherwise reflect off optical surfaces and enter the eye, effectively separating harmful stray light from the useful image light path.
Solution Approach 2:
The patent introduces intermediary optical elements including polarizing beamsplitters and waveplates that mediate between the displayed image and the user's eye. These intermediaries control the polarization state of light and selectively direct image light while blocking stray light paths.
2Device complexity
If dark state light is allowed to reflect off optical surfaces, then the optical system remains simple, but black areas of the displayed image appear gray and contrast is reduced
Solution Approach 1:
The patent converts the harmful dark state light into a useful signal by using polarizing beamsplitters to separate it from image light. The dark state light, which would normally be wasted or harmful, is now directed to a light trap in a controlled manner, enabling effective stray light suppression while maintaining optical efficiency.
Solution Approach 2:
The patent changes the polarization state of light using waveplates and polarizing beamsplitters. By manipulating polarization parameters, the system can selectively direct different light paths (image light vs. dark state light) through different optical routes, enabling contrast enhancement without excessive complexity.
3Use of energy by moving object
If multiple optical surfaces are used to deliver the displayed image, then image delivery efficiency is improved, but each surface reflects stray light that accumulates and degrades image quality
Solution Approach 1:
The patent extracts stray light at each optical surface using polarizing beamsplitters that separate image light from reflected dark state light. This continuous extraction of stray light along the optical path prevents accumulation and maintains high contrast throughout the system.
Solution Approach 2:
The patent applies polarization control elements in advance before stray light can accumulate. The polarizing beamsplitters and waveplates are positioned to preemptively separate and trap dark state light before it can reflect multiple times and degrade image quality.
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 configuration enhances image contrast and reduces stray light, resulting in sharper, darker blacks and improved see-through capabilities by effectively isolating dark state light from the image light path.
Implementation Method 1
an optical system that includes a DLP-based upper optical module with a polarized light source, reflective polarizer, and a quarter-wave retarder film
Implementation Method 2
reflective polarizer
Implementation Method 3
a light trap to manage stray light by directing dark state light away from the optical axis
Data Source
AI summary
Aspects of the present invention relate to providing see-through computer display optics.