Polarized HUD Reflector Structure for Ghost Image Suppression
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Solution Overview
Problem
Current head-up display (HUD) systems face issues with ghost images and glare due to demagnified and magnified secondary images caused by stray light from strong illumination sources, which affect the observer's visual experience and optical performance, particularly in automotive windshields.
Innovation Solution
A layered optical structure is implemented, comprising a plano-convex lens, a polarization manipulating layer, and a plano-concave lens with two half-wave retarder plates oriented orthogonally to enhance reflectance efficiency for Transverse Electric (TE) polarization while minimizing reflectance for Transverse Magnetic (TM) polarization, reducing ghost images and glare.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a partially reflective medium is used in the HUD system to reflect light for the display image, then the optical performance (field of view, exit pupil) is improved, but ghost images and secondary reflections are generated that degrade visual quality
Solution Approach 1:
The patent changes the polarization state parameter of light by introducing wave retarders that transform TM-polarized light to TE-polarized light and vice versa. This parameter transformation allows the system to exploit the polarization-dependent reflectance properties of the partially reflective medium, enabling high reflectance for the display image while minimizing ghost reflections from external light sources.
Solution Approach 2:
The wave retarders act as intermediary elements that mediate between the incident light and the partially reflective medium. By transforming the polarization state before light interacts with the reflective coating, these intermediaries enable selective control over reflection and transmission, reducing harmful ghost images while maintaining display image quality.
2Illumination intensity
If the reflectivity of the partially reflective medium is increased to improve image contrast, then the display visibility is improved, but more light is reflected creating stronger ghost images and reducing see-through performance
Solution Approach 1:
The patent transforms the polarization parameter of incident light using wave retarders, converting TM-polarized light to TE-polarized light before it reaches the partially reflective medium. Since the reflective coating has different reflectance characteristics for different polarization states, this parameter transformation enables high reflectance (improving image contrast) for the display image while the external light sources produce minimal ghost reflections due to their different polarization states after transformation.
3Object-generated harmful factors
If Brewster angle incidence is used to eliminate ghost reflections from the windscreen surface, then ghost image reduction is achieved, but the optical path geometry becomes more complex and field of view is limited
Solution Approach 1:
Instead of relying on geometric parameter changes (Brewster angle incidence), the patent uses polarization state parameter changes achieved through wave retarders. This allows the system to maintain simpler optical geometry with broader field of view while still achieving ghost reflection reduction through polarization-selective reflectance properties of the partially reflective medium.
4Adaptability or versatility
If a giant lens is integrated into the windscreen to enhance field of view and head motion box, then optical performance is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent segments the optical functionality into separate components: the windscreen maintains its primary function as a transparent barrier, while the HUD optical elements (partially reflective medium, wave retarders) are integrated as distinct functional layers. This segmentation avoids the complexity of integrating a giant lens into the windscreen structure, simplifying both device complexity and manufacturing while achieving the desired field of view enhancement through the HUD optical path.
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 power of secondary images, from 1.5% to less than 0.6%, and eliminates magnified ghost images, maintaining efficient reflectance for TE polarization while minimizing TM polarization reflections, thereby improving the optical performance and reducing visual artifacts in HUD systems.
Implementation Method 1
a first polarization manipulating layer adjoining said first layer and adapted to transform the polarization state of said polarized light
Implementation Method 2
the angle between the incidence angle and the optical axis of the plano-convex lens satisfies a Brewster angle
Implementation Method 3
an optical partial reflective filter that is designed according to the polarization and reflectivity requirements
Implementation Method 4
a plano-convex lens... a plano-concave lens, conjugated to the first plano-convex lens
Data Source
AI summary
A layered structure for manipulating optical polarization for a head-up display application is provided herein. The layered structure includes: a Picture Generating Unit “PGU”, the structure adapted to receive polarized light oriented along a Transverse Magnetic “TM” polarization direction, from said PGU, said structure comprising: a first layer comprising a plano-convex lens, wherein the angle between the incidence angle and the optical axis of the plano-convex lens satisfies a Brewster angle; a first polarization manipulating layer adjoining said first layer and adapted to transform the polarization state of said polarized light; an optical partial reflective filter that is designed according to the polarization and reflectivity requirements; and a plano-concave lens, conjugated to the first plano-convex lens.