HUD Windshield Reflective Polarizer for Ghost Image Reduction
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Solution Overview
Problem
HUD systems face challenges in minimizing ghost images due to horizontal skew angles, particularly in wide field of view applications, where the polarization of light is rotated away from the fast/slow axis of birefringent windshield combiner films, leading to increased retardation and ghost reflections.
Innovation Solution
Applying a bias angle to the orientation of the windshield combiner film (WCF) to minimize retardation effects and reduce ghost reflections by aligning incident light with its plane of incidence, using a reflective polarizer embedded in the windshield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional HUD system with separate windshields and combiners is used, then the display function is achieved, but the device complexity and number of components increase
Solution Approach 1:
The patent combines the windshield and combiner into a single integrated optical element. The windshield includes both the transparent substrate and the reflective layer pattern formed directly on it, eliminating the need for separate combiner components. This merging reduces device complexity while maintaining the head-up display function through the integrated reflective and transmissive optical paths.
Solution Approach 2:
The windshield serves multiple functions simultaneously: it acts as both the protective transparent barrier and the optical combiner for reflecting HUD images. The reflective layer pattern on the windshield enables both image reflection and maintains optical transparency where needed, allowing a single component to perform what traditionally required multiple specialized parts.
2Illumination intensity
If the HUD system uses a reflective layer on the windshield, then the display visibility is improved, but the manufacturing precision requirements increase due to alignment constraints
Solution Approach 1:
The reflective layer is formed directly on the windshield substrate during the manufacturing process before final assembly. This preliminary formation ensures precise alignment between the reflective pattern and the windshield geometry, eliminating subsequent alignment issues that would arise from attaching separate combiner layers. The pattern is deposited with controlled positioning to ensure proper optical alignment.
Solution Approach 2:
The reflective layer is nested within the windshield structure itself, forming an integrated layered composition. The reflective material is deposited as a thin layer on the inner surface of the windshield, creating a nested configuration where the functional layer is contained within the structural component, ensuring inherent alignment and eliminating separate positioning requirements.
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 both front and back ghost contrast ratios by minimizing the S-pol component of light on reflecting surfaces, enhancing the HUD's field of view and image clarity.
Implementation Method 1
a first optical element of the optical system is arranged to receive light from a first light source and to refract the light towards a second optical element
Implementation Method 2
a second optical element of the optical system is arranged to receive the light from the first light source and to reflect the light towards a third optical element
Implementation Method 3
a third optical element of the optical system is arranged to receive the light from the first light source and to refract the light towards a fourth optical element
Data Source
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AI summary
An optical system includes a display including an active display region configured to emit an image. The active display region includes a predetermined region including a display center. A windshield of a vehicle includes an embedded reflective polarizer. The reflective polarizer reflects between about 20% to about 40% of incident light polarized along a first direction, and transmits at least 60% of the incident light polarized along a second direction. The reflective polarizer receives the image emitted by the active display region and reflects a portion toward the eye. For at least one first location within the predetermined region, the emitted image includes an image cone having an emitted central image ray emitted from the first location. The emitted central image ray is polarized along a third direction when incident on the windshield in an incident plane. The first and third directions are substantially parallel to the incident plane.