Switchable Waveguide HUD Gratings for Eyebox-Targeted Illumination
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Solution Overview
Problem
Conventional waveguide-based projection display devices, such as Head-Up Displays (HUDs), suffer from inefficient light utilization and high electrical energy consumption due to fixed diffraction efficiency in the folding grating, which illuminates areas outside the viewer's eyebox, necessitating high power requirements and costly laser light sources.
Innovation Solution
A waveguide-based projection display device with a folding grating divided into independently switchable segments, controlled by an eye-tracking unit to generate a temporally variable spatial gradient of diffraction efficiency, ensuring light is directed only to the viewer's eyebox, reducing power requirements by at least 50%.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional waveguide with fixed diffraction efficiency is used to illuminate the entire eyebox, then the virtual display image is visible across the full eyebox area, but light is wasted in areas where the viewer's eyes are not located, resulting in high energy consumption and the need for expensive laser light sources
Solution Approach 1:
The folding grating is divided into multiple independently controllable segments along the beam propagation direction. Each segment can be individually activated or deactivated based on the viewer's eye position, allowing the system to illuminate only the relevant portion of the eyebox rather than the entire area, thus reducing light power requirements while maintaining sufficient luminance where needed
Solution Approach 2:
The system dynamically adjusts which grating segments are active based on real-time eye position detection. This dynamic reconfiguration allows the illumination pattern to adapt to the viewer's location, ensuring high luminance in the active eyebox region while minimizing light power consumption by deactivating segments that would otherwise waste light in unused areas
2Adaptability or versatility
If the entire folding grating is activated to ensure homogeneous illumination across the full eyebox, then the display is visible to viewers at any position within the eyebox, but the system consumes maximum energy and requires expensive laser light sources
Solution Approach 1:
By segmenting the folding grating into controllable sections, the system can selectively activate only the segments corresponding to the current eyebox region. This maintains adaptability to viewer position while avoiding energy waste in segments that would illuminate areas outside the active eyebox, thereby reducing electrical energy consumption
Solution Approach 2:
Different segments of the folding grating are activated based on local requirements - only the segments that contribute to illuminating the current eyebox position are enabled. This local quality approach ensures adequate eyebox coverage where needed while minimizing energy loss in regions that do not require illumination
3Ease of manufacture
If a conventional waveguide HUD with fixed diffraction efficiency gradient is used, then the system structure is simple and manufacturing is easier, but light utilization efficiency is low and power requirements are high
Solution Approach 1:
The folding grating is segmented into multiple independently controllable sections. While this increases manufacturing complexity compared to a fixed grating, it dramatically improves light utilization efficiency by allowing selective activation of only those segments that contribute to the current eyebox, thereby reducing power requirements and energy waste
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 achieves significant cost and energy savings by optimizing light utilization, allowing for the use of less powerful light sources and reducing electrical consumption, particularly beneficial in vehicle applications.
Implementation Method 1
A light beam L generated by an imaging unit 2 enters the waveguide 3, which is designed as a glass plate, via its coupling grating 4. From the grating, it is deflected so that it propagates through the glass by total internal reflection
Implementation Method 2
From the grating, it is deflected so that it propagates through the glass by total internal reflection
Implementation Method 3
enters the area of a folding grating 5. In the folding grating 5, the light beam L is successively deflected towards an output grating 6
Implementation Method 4
In the output grating 6, it is deflected so that it exits the glass plate towards a windshield 7 of the vehicle
Implementation Method 5
exits the glass plate towards a windshield 7 of the vehicle, from which it is reflected to the user 8, in this case, the driver
Data Source
Figure 1~2
Figure 3~4a
Figure 4b
AI summary
The invention relates to a waveguide-based projection display device for a vehicle, comprising: - an image-producing unit; - a planar waveguide, which has an extensive outcoupling grating, an incoupling grating located laterally to the outcoupling grating, and a fold grating located therebetween for successively deflecting the incoupled light to the outcoupling grating; - an at least partially transparent reflection panel for reflecting a light beam bundle, which is coupled out from the waveguide, to a two-dimensional eye-box so that, in the field of vision of a user, a virtual display image is created behind the reflection panel; - an eye-tracking apparatus for determining a currently occupied eye-box window within the eye-box; wherein the fold grating is divided, in the beam propagation direction corresponding to an eye-box height direction, into a plurality of segments which can be switched, independently of each other, into a light-deflecting state, and wherein the device is designed to switch on only some of the segments at a time and with different diffraction efficiency from each other so that the light beam bundle is restricted, in the eye-box height direction, to the eye-box window and evenly illuminates the eye-box window.