Head-Up Display Optics Using a Cholesteric Mirror for Luminance Retention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing head up displays (HUDs) experience a decrease in luminance when the liquid crystal panel is tilted relative to the orthogonal direction, compromising the stereoscopic effect of the virtual image.
Innovation Solution
Incorporating a semi-reflective mirror with a cholesteric liquid crystal layer that transmits and reflects light, forming an acute angle with the display panel, and utilizing a configuration of mirrors and wave plates to maintain the stereoscopic effect while reducing luminance loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the liquid crystal panel is tilted relative to the orthogonal direction to increase the stereoscopic effect, then the stereoscopic effect is improved, but the luminance of the virtual image decreases
Solution Approach 1:
A semi-reflective mirror is introduced as an intermediary component between the display panel and the projection optical system. This mirror has a specific angle of incidence (45 degrees or less) that allows it to reflect light from the display panel while maintaining a longer optical path length. The semi-reflective mirror acts as a mediator that decouples the panel tilt angle from the optical path geometry, enabling the panel to be tilted for stereoscopic effect without directly causing luminance loss through short optical paths.
Solution Approach 2:
The invention changes the dimensional relationship between the display panel and the optical path by introducing a semi-reflective mirror at a specific angle. Instead of directly tilting the panel relative to the optical axis, the system uses the mirror's angle of incidence to create a separate geometric dimension for light reflection. This allows the panel tilt and mirror reflection to be independently optimized - the panel can be tilted for stereoscopic effect while the mirror maintains optimal reflection geometry for luminance.
2Shape
If the liquid crystal panel is tilted to enhance the stereoscopic effect, then the virtual image depth is improved, but the optical path length decreases causing luminance loss
Solution Approach 1:
The semi-reflective mirror serves as a geometric intermediary that extends the optical path length. By positioning the mirror at a specific angle (45 degrees or less) relative to the optical axis, the light path from the display panel to the projection lens is lengthened through the reflection process. This mediator allows the system to achieve both a tilted panel configuration for virtual image depth and a sufficiently long optical path for maintaining luminance.
3Device complexity
If a simple tilt configuration is used, then the device complexity is reduced, but the luminance decrease cannot be sufficiently mitigated
Solution Approach 1:
The invention optimizes specific geometric parameters to achieve luminance improvement without excessive complexity. The semi-reflective mirror is positioned at a specific angle of incidence (45 degrees or less) relative to the optical axis, and the display panel is tilted at a specific angle (15 degrees or more) relative to the orthogonal direction. These parameter optimizations create a balance point where the additional component complexity is justified by the significant luminance improvement while maintaining reasonable device complexity.
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 maintains the stereoscopic effect of the virtual image while reducing luminance loss by optimizing the optical path lengths and using a cholesteric liquid crystal layer to enhance image brightness and clarity.
Implementation Method 1
The semi-reflective mirror includes a cholesteric liquid crystal layer that is configured to transmit light from the display panel and reflect light from the first mirror
Implementation Method 2
a first mirror that is configured to reflect light having passed through the display panel
Data Source
AI summary
According to an aspect, a head up display includes, inside a case: a display panel that is configured to emit light to project an image; a first mirror that is configured to reflect light having passed through the display panel; and a semi-reflective mirror provided between the display panel and the first mirror. The semi-reflective mirror includes a cholesteric liquid crystal layer that is configured to transmit light from the display panel and reflect light from the first mirror. An acute angle is formed between a surface of the semi-reflective mirror through which light from the display panel is transmitted and a surface of the display panel through which light from the display panel is emitted.