See-through HMD Stray Light Management via Polarization
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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 scattering light within the optics, causing black areas to appear gray and affecting the see-through view of the environment.
Innovation Solution
The implementation of advanced optical modules with dark light traps and polarized light management systems, such as TIR wedges and reflective polarizers, to redirect and absorb stray light, enhancing image contrast and clarity while maintaining a clear see-through view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If see-through optics are used in HMDs, then environmental visibility is improved, but stray light scattering occurs which reduces image sharpness and contrast
Solution Approach 1:
A polarizing beam splitter is introduced as an intermediary optical element that separates light into polarized components. This mediator allows the system to distinguish between desired image light and unwanted stray light, enabling both see-through capability and high image quality without direct conflict between the two functions.
Solution Approach 2:
The patent employs polarization state manipulation to change the optical parameters of light passing through the system. By controlling the polarization angle and using polarizing filters, the system can selectively transmit or block light based on its polarization state, thereby maintaining both environmental visibility and image contrast through parameter-based differentiation.
2Manufacturing precision
If stray light is reduced using traditional methods, then image contrast is improved, but the see-through view quality deteriorates
Solution Approach 1:
The polarizing beam splitter acts as a selective intermediary that allows different light paths to coexist. It mediates between the see-through path (transmitting environmental light) and the display path (blocking stray light), enabling both functions to operate simultaneously without compromising either image contrast or see-through quality.
Solution Approach 2:
Different regions of the optical system are assigned different polarization properties. The beam splitter and associated polarizing elements create localized polarization control zones that selectively manage light transmission in different areas, allowing high contrast in the displayed image while maintaining full transparency for the see-through view in other regions.
3Manufacturing precision
If polarized light management systems are implemented, then stray light is reduced and contrast is enhanced, but device complexity increases
Solution Approach 1:
The polarizing beam splitter serves multiple functions simultaneously: it acts as a beam splitter, a polarizer, and a stray light blocker all in one component. This multi-functionality reduces the need for separate optical elements, thereby managing device complexity while achieving superior 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 effectively reduces stray light, achieving high contrast and deep blacks in displayed images while preserving the see-through view, providing a more immersive and clear augmented reality experience.
Implementation Method 1
TIR wedges and reflective polarizers, to redirect and absorb stray light
Implementation Method 2
TIR wedges and reflective polarizers, to redirect and absorb stray light
Implementation Method 3
dark light traps and polarized light management systems, such as TIR wedges and reflective polarizers, to redirect and absorb stray light
Data Source
AI summary
A see-through head mounted display with controllable light blocking includes an optics module comprising a light source and image source positioned on a same side of an angled partially-reflective surface, wherein the light source projects light off the surface to the image source which reflects the light as image light to the surface which transmits the image light along a first axis. The display also includes a flat combiner positioned to reflect the image light off of a first side and simultaneously transmit incident light through the first and a second side, along an optical axis perpendicular to the first axis to provide a view of a displayed image overlaid onto a see-through view of the environment, and a controllable light blocking element arranged generally parallel to the flat combiner and in front of the second side to block light incident on the same optical axis as the image light.