Cholesteric Liquid Crystal Reflection Layer for Head-Up Display Double Image Elimination
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Solution Overview
Problem
Existing head-up display systems face challenges in eliminating double images caused by light reflection, while maintaining high reflectance and transmittance, particularly in windshield glass applications.
Innovation Solution
A member for projection image display is developed using a cholesteric liquid crystal layer as a reflection layer, combined with a retardation layer, to selectively reflect circularly polarized light, thereby eliminating double images and achieving high brightness and tint balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional reflection layer is used in windshield glass, then high reflectance of projection light can be achieved, but double images occur due to surface and rear surface reflections
Solution Approach 1:
The patent applies Brewster's angle principle by setting the incident light angle to approximately 56 degrees, which causes p-polarized light to be transmitted through the glass surface with minimal reflection. This parameter change in incident angle eliminates the harmful surface reflection that causes double images, while maintaining high projection light reflectance through the cholesteric liquid crystal layer
Solution Approach 2:
The patent uses a cholesteric liquid crystal layer that exhibits circularly polarized selective reflection, creating different optical properties for different polarization states. The layer selectively reflects s-polarized light while transmitting p-polarized light, providing local quality differentiation that eliminates double images while maintaining high reflectance for the projection system
2Object-generated harmful factors
If Brewster's angle is utilized to eliminate double images, then surface reflection is reduced, but simultaneous securing of sufficient light reflectance and light transmittance remains problematic
Solution Approach 1:
The patent combines multiple functional layers including a cholesteric liquid crystal layer, a retardation layer, and windshield glass to create a composite optical system. The cholesteric liquid crystal layer provides circularly polarized selective reflection with high reflectance, while the retardation layer converts linear polarization to circular polarization, and the glass provides structural support and additional optical functions, achieving both high reflectance and transmittance simultaneously
Solution Approach 2:
The retardation layer acts as an intermediary between the incident linearly polarized light and the cholesteric liquid crystal layer. It converts the linearly polarized light into circularly polarized light, which then interacts with the cholesteric liquid crystal layer's selective reflection property, enabling the system to achieve both high reflectance and transmittance that cannot be achieved with a single layer
3Object-generated harmful factors
If a cholesteric liquid crystal layer is used as reflection layer, then selective reflection of circularly polarized light is achieved, but high brightness and tint balance are difficult to obtain simultaneously
Solution Approach 1:
The patent employs a variable retardation layer whose optical properties can be dynamically adjusted to optimize the conversion of linearly polarized light to circularly polarized light. By controlling the retardation value, the system can dynamically adjust the amount of light reflected versus transmitted, achieving both high brightness for the projection image and proper tint balance for visible light while eliminating double images
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 provides a clear, high-brightness projection image with excellent tint balance and high transmittance, even when observed with polarized sunglasses, effectively addressing the issue of double images in head-up display systems.
Implementation Method 1
a cholesteric liquid crystal layer which has a function of a reflection layer and exhibits circularly polarized selective reflection
Implementation Method 2
a λ/4 retardation layer that changes linearly p-polarized light to circularly polarized light
Implementation Method 3
bringing, close to zero, reflected light from the surface of a member for projection image display while utilizing Brewster's angle, to thereby eliminate a double image
Data Source
AI summary
The present invention provides a member for projection image display, including a reflection layer and a retardation layer, wherein the reflection layer includes a cholesteric liquid crystal layer exhibiting selective reflection in a visible light region, the cholesteric liquid crystal layer is a layer formed from a liquid crystal composition containing a discotic liquid crystal compound, and a front phase difference of the retardation layer is in a range of 50 nm to 400 nm; and a projection image display system which includes the above member for projection image display, wherein the retardation layer is disposed on an incident light side relative to the reflection layer, and the incident light is p-polarized light that vibrates in a direction parallel to a plane of incidence, which is capable of displaying a clear image having high reflectance and high transmittance, without a problem of a double image.