HUD Combiner Polarizing Layer for Double Image Suppression
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Solution Overview
Problem
Traditional head-up displays (HUDs) often suffer from double images due to reflections from the back surface of the combiner, which can be exacerbated by factors like rain or contaminant buildup on vehicle windshields used as combiners, particularly in curved designs.
Innovation Solution
Incorporating a polarizing layer with a tilted axis within the combiner to attenuate refracted rays before they reach the back surface, reducing or eliminating double images by adjusting the output polarization to favor P-polarization and using additional coatings or retardation layers to manage reflections effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a combiner is used to reflect the projected image, then the field of view and projected infinity image are visible simultaneously, but double images are generated due to reflections from the back surface of the combiner
Solution Approach 1:
The patent converts the harmful back-surface reflection into a beneficial effect by using a polarizing beam splitter in conjunction with a quarter-wave plate. The quarter-wave plate transforms linearly polarized light into circularly polarized light, which then reflects off the back surface and returns as linearly polarized light perpendicular to the original polarization direction. This allows the polarizing beam splitter to direct the reflected light to a different location, effectively using the previously harmful reflection to create a controlled optical path that eliminates double images while maintaining visibility.
Solution Approach 2:
The patent changes the polarization state of light as it passes through the optical system. By introducing a quarter-wave plate, the light's polarization parameter is transformed from linear to circular and back to linear with a 90-degree rotation. This parameter change enables the system to distinguish between forward and reflected light paths using a polarizing beam splitter, thereby eliminating the double image problem while preserving the combiner's reflective function.
2Shape
If the combiner is made curved to match the windshield shape, then it integrates with the vehicle structure, but double images are exacerbated by rain or contaminant buildup on the windshield
Solution Approach 1:
The polarizing beam splitter system converts reflections from contaminants or rain on the windshield into useful optical signals. By controlling the polarization state of reflected light, the system can direct these reflections away from the driver's line of sight or to a different display location, transforming what would be distracting double images into controlled optical paths that maintain image quality even in adverse weather conditions.
Solution Approach 2:
The system uses polarization parameter changes to differentiate between light paths. The quarter-wave plate and polarizing beam splitter combination modifies the polarization state of light reflecting off contaminants or rain, allowing the system to control where these reflections appear. This enables the curved combiner to maintain its integrated shape while suppressing harmful reflections from environmental contaminants.
3Manufacturing precision
If sophisticated optics are used to meet performance requirements, then precise angular control and uniformity are achieved, but the size, weight and cost of the HUD increase
Solution Approach 1:
The patent merges multiple optical functions into a single integrated combiner assembly. The polarizing beam splitter and quarter-wave plate are combined with the combiner itself, eliminating the need for separate components to handle reflection and polarization control. This integration maintains precise angular control and image uniformity while reducing the overall size and weight of the HUD system by consolidating optical elements.
Solution Approach 2:
The combiner assembly is designed to perform multiple functions simultaneously: reflecting the projected image, controlling polarization states, managing back-surface reflections, and maintaining precise angular control. By making the combiner a multi-functional element that incorporates the polarizing beam splitter and quarter-wave plate, the system achieves sophisticated optical performance without adding separate heavy components, thus reducing overall system weight and size.
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 suppresses double images while maintaining high transmittance and clarity of the outside scene, even in adverse conditions, by attenuating refracted rays before they cause reflections, thus enhancing the HUD's performance and user experience.
Implementation Method 1
Incorporating a polarizing layer with a tilted axis within the combiner to attenuate refracted rays before they reach the back surface
Implementation Method 2
The combiner reflects the image projected by the projector in such a way as to see the field of view and the projected infinity image at the same time
Implementation Method 3
the HUD will typically include an optical collimator, such as a convex lens or concave mirror, to produce an image that is perceived to be at infinity
Data Source
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AI summary
A head-up display system and method are provided that suppress double images from a combiner by eliminating or reducing a reflection of a refracted image from the back surface of the combiner. The combiner contains a tilted axis polarizing structure that attenuates transmittance and subsequent reflection of a refracted polarized projector image but maintains high transmittance for the forward external scene imagery.