Head-Up Display Light Guide Pupil Expansion With Easier Grating Fabrication
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Solution Overview
Problem
Manufacturing of pupil expansion type light guide bodies for head-up displays is challenging due to the need for fine processing, which is difficult to achieve.
Innovation Solution
A head-up display system with a light guide body that includes a coupling region, a first expansion region, and a second expansion region, utilizing diffraction gratings to replicate light fluxes in different directions, facilitating easy manufacturing by reducing the diffraction power and pitch of the grating elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a pupil expansion type hologram is used for head-up display, then the visual recognition region can be expanded, but fine processing is required for the light guide body making it difficult to manufacture
Solution Approach 1:
The light guide body is divided into multiple functional regions: a coupling region for receiving light from the display, a first expansion region for expanding the light flux in a first direction, and a second expansion region for expanding the light flux in a second direction. This segmentation allows each region to have optimized grating characteristics, reducing the overall manufacturing difficulty while achieving pupil expansion in multiple directions.
Solution Approach 2:
Different regions of the light guide body are assigned different local properties: the coupling region has grating elements with specific pitch and diffraction power for light coupling, the first expansion region has grating elements optimized for expansion in the first direction, and the second expansion region has grating elements optimized for expansion in the second direction. This local quality approach allows each region to be manufactured with appropriate precision requirements, reducing overall manufacturing difficulty.
2Area of stationary object
If diffraction gratings with high diffraction power are used to expand visual recognition region, then the expansion effect is improved, but the processing precision requirements increase making manufacturing difficult
Solution Approach 1:
The pupil expansion function is segmented across multiple regions with different diffraction powers. The coupling region uses grating elements with higher diffraction power for efficient light coupling, while the expansion regions use grating elements with lower diffraction power for gradual light flux expansion. This segmentation reduces the manufacturing precision requirements for each individual region while achieving the overall expansion goal.
Solution Approach 2:
Instead of using a single high-power diffraction grating to achieve all expansion in one step, the system applies multiple partial expansion actions through sequential regions. The first expansion region provides partial expansion in the first direction, and the second expansion region provides partial expansion in the second direction, collectively achieving the desired visual recognition region expansion with lower precision requirements for each region.
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 system enables easy manufacturing of the light guide body by reducing the diffraction power and pitch of grating elements, allowing for efficient expansion of the visual recognition region and improved visibility of virtual images superimposed on the real view.
Implementation Method 1
Light from the display (10) enters the coupling region (33) and is guided through the light-guiding plate (31) by total internal reflection
Implementation Method 2
The optical element may utilize a diffractive optical element to expand the exit pupil
Implementation Method 3
Document 2 describes a head-mounted display that performs augmented reality (AR) display using a volume hologram diffraction grating
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A head-up display system includes a display that emits a light flux visually recognized by an observer as the virtual image, and a light guide body that guides the light flux to the light-transmitting member. The light guide body includes an incident surface on which the light flux from the display is incident and an emission surface from which the light flux is emitted from the light guide body. The light flux incident on the incident surface of the light guide body is changed in a traveling direction in the light guide body, the light flux is replicated into a plurality of light fluxes in a direction perpendicular to a horizontal direction of the virtual image visually recognized by the observer to be emitted from the emission surface so as to expand a visual recognition region. When a direction indicated by a normal on the visual recognition region side in a normal direction of the light-transmitting member at an intersection of the light-transmitting member and the Z-axis is defined as a direction A, and a direction connecting a center of the visual recognition region of the virtual image and an emission port of the display is defined as a direction B, the direction A and the direction B intersect each other in the XZ plane between the visual recognition region and the light-transmitting member.