HUD Windshield Polarizer Bias Angle for Skew-Angle Ghosts
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Solution Overview
Problem
HUD systems experience significant ghost images due to horizontal skew angles, leading to increased polarization rotation and back ghost reflections, which degrade the visibility of primary virtual images, especially at wider field of view angles.
Innovation Solution
Incorporating a bias angle into the WCF orientation within the windshield glass laminate to minimize retardance effects and shift the skew-angle region of minimal back ghost reflection, combined with HUD image output polarization tuning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a reflective polarizer is used in the windshield to display HUD images, then the image visibility is improved, but ghost images and back ghost reflections increase due to horizontal skew angles
Solution Approach 1:
The patent introduces a bias angle (e.g., 5 degrees) to the WCF orientation within the windshield glass laminate, creating an asymmetric configuration that minimizes retardance effects and shifts the skew-angle region of minimal back ghost reflection. This asymmetric orientation compensates for the symmetric polarization rotation caused by horizontal skew angles, thereby reducing ghost images while maintaining image visibility.
Solution Approach 2:
The patent adjusts the polarization tuning of the HUD image output to work in conjunction with the biased WCF orientation. By changing the polarization parameters of the emitted light to match the biased orientation, the system optimizes the interaction between the HUD image and the windshield, minimizing retardance effects and reducing both front and back ghost contrast ratios.
2Area of moving object
If the field of view angle is increased to provide wider viewing, then the coverage is improved, but polarization rotation increases leading to degraded image visibility
Solution Approach 1:
The biased WCF orientation creates an asymmetric optical path that differentially affects light rays at different skew angles. This asymmetric configuration minimizes the cumulative polarization rotation effect across the field of view, allowing wider viewing angles to be achieved without the same degree of image visibility degradation that would occur with a symmetric (zero-bias) configuration.
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
Significantly reduces both front and back ghost contrast ratios by reducing the S-pol component of light incident on reflecting surfaces, enhancing image clarity and visibility across various skew angles.
Implementation Method 1
For substantially normally incident light and for at least one wavelength between about 420 nm and about 670 nm, the reflective polarizer reflects between about 20% to about 40% of the incident light polarized along a first direction, and transmits at least 60% of the incident light polarized along an orthogonal second direction
Implementation Method 2
The reflective polarizer is configured to receive the image emitted by the active display region and reflect a portion of the received image toward the eye
Implementation Method 3
Incorporating a bias angle into the WCF orientation within the windshield glass laminate to minimize retardance effects and shift the skew-angle region of minimal back ghost reflection
Data Source
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.