Windshield Polarizer Layout for HUD Ghost Image Mitigation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing heads-up displays in vehicles suffer from ghosting issues, particularly at large viewing angles, due to multiple reflections off the windshield layers, which degrade the visual quality of the intended image.
Innovation Solution
Incorporating a reflective polarizer adjacent to the windshield's outermost glass surface and a phase retarding plate in the optical path between the display and windshield, adjusting the polarization state of the reflected image to improve viewing characteristics based on the viewing angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a windshield with multiple glass layers is used to provide structural strength and safety, then the strength and reliability of the windshield is improved, but ghost images appear due to multiple reflections, worsening the visual quality of the HUD image
Solution Approach 1:
A reflective polarizer is introduced as an intermediary layer between the display and the windshield's glass layers. This polarizer selectively reflects the desired image while the quarter-wave plate modifies the polarization state to control reflections from different glass surfaces, thereby eliminating ghost images while maintaining the multi-layer glass structure for strength
Solution Approach 2:
The patent changes the polarization state of light using a quarter-wave plate, transforming linearly polarized light from the display into circularly polarized light before it reaches the windshield. This parameter change in polarization state allows the reflective polarizer to differentiate between the desired image path and unwanted reflection paths, eliminating ghosting while preserving the multi-layer glass structure
2Illumination intensity
If the reflective polarizer reflects a high percentage of the emitted image to improve image intensity, then the brightness of the HUD image is improved, but the viewing angle characteristic deteriorates at wider viewing angles
Solution Approach 1:
The quarter-wave plate changes the polarization parameter of the light, converting linear polarization to circular polarization. This enables the reflective polarizer to maintain high reflectivity for the intended image while reducing sensitivity to viewing angle variations, thereby improving both image intensity and viewing angle characteristics simultaneously
Solution Approach 2:
The patent replaces traditional optical elements with a polarization-based system. Instead of using multiple reflective surfaces or complex optical paths, the invention uses the interaction between polarized light and the reflective polarizer to control image reflection, achieving wide viewing angle characteristics with high image intensity
3Strength
If layers with greater thickness are added on the reflective polarizer to improve durability and protection, then the strength and protection are improved, but the average thickness exceeds 7 microns, worsening the ghost image reduction effectiveness
Solution Approach 1:
The patent employs an ultrathin protective layer (less than 7 microns thick) on the reflective polarizer that provides necessary protection and durability while maintaining optical transparency. This thin film approach eliminates ghost images by avoiding thick layers that would create additional reflection interfaces, while still providing adequate mechanical protection
Solution Approach 2:
The patent optimizes the thickness parameter of the protective layer to be less than 7 microns, which is a critical threshold. By controlling this dimensional parameter, the system achieves both protection durability and ghost image reduction, as thinner layers minimize additional reflection interfaces while maintaining structural integrity
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
Reduces ghost images and enhances image intensity for both the driver and front-seat passenger, optimizing the display for different viewing angles and conditions, including when passengers wear polarized sunglasses.
Implementation Method 1
a phase retarding plate disposed in an optical path between the display and the windshield. The phase retarding plate modifies a polarization state of the reflected image
Implementation Method 2
a reflective polarizer disposed adjacent to a first outermost glass surface of the windshield... The reflective polarizer is configured to transmit at least 60% of an incident light having a wavelength from received polarized image and having a second polarization state orthogonal to the first polarization state
Data Source
AI summary
A heads-up display for viewing by an eye of a passenger of a vehicle includes a windshield with a reflective polarizer disposed adjacent to a first outermost glass surface of the windshield, a display configured to emit an image toward the windshield, the windshield reflecting between 15% and 85% of the emitted image toward the passenger, and a phase retarding plate disposed in an optical path between the display and the windshield. The windshield is configured to receive the image emitted by the display after the image has been transmitted by the phase retarding plate and to reflect at least a portion of the received image as a reflected image toward the eye of the passenger. The phase retarding plate modifies a polarization state of the reflected image to improve a viewing characteristic of the reflective image depending on a viewing angle of the eye of the passenger.