Light Guide HUD Optics for Higher Diffraction Efficiency
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Solution Overview
Problem
Conventional head-up display systems using pupil expansion type holograms suffer from low diffraction efficiency due to transmission type diffraction structures.
Innovation Solution
An optical system with a light guide body featuring a coupling region, a first expansion region, and a second expansion region, where the light flux is diffracted and replicated in both horizontal and vertical directions, with specific diffraction structural elements and angles to enhance diffraction efficiency, and a head-up display system that incorporates this optical system to project virtual images onto a windshield for improved viewing angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a transmission type diffraction structure is used in a head-up display, then the device complexity is reduced, but the diffraction efficiency becomes low
Solution Approach 1:
The patent transitions from a two-dimensional transmission type diffraction structure to a three-dimensional reflection type diffraction structure. The diffraction structure is formed with multiple layers having different refractive indices and diffraction grating patterns, creating a volumetric optical element that reflects and diffracts light more efficiently while maintaining a compact form factor suitable for head-up displays.
Solution Approach 2:
The patent employs a composite structure consisting of multiple layers with different optical properties. Each layer has a specific refractive index and diffraction grating configuration, creating a multi-material optical system that enhances overall diffraction efficiency. The combination of layers with alternating high and low refractive indices creates constructive interference patterns that improve light utilization.
2Manufacturing precision
If the diffraction structure is optimized for higher diffraction efficiency, then the display quality improves, but the manufacturing precision requirements increase
Solution Approach 1:
The patent divides the diffraction structure into multiple discrete layers, each with a specific function. The first layer has a first diffraction grating, the second layer has a second diffraction grating, and each layer can be manufactured and optimized independently. This segmentation allows for more precise control of optical properties in each layer while simplifying the overall manufacturing process through modular construction.
Solution Approach 2:
The patent optimizes diffraction efficiency by carefully controlling key parameters including the thickness of each layer, the refractive index of materials, the pitch and orientation of diffraction gratings, and the spacing between layers. By adjusting these parameters, the system achieves high diffraction efficiency while maintaining manufacturability through standard optical fabrication techniques.
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 optical system significantly improves diffraction efficiency by preventing interference between diffracted light fluxes, allowing for wider viewing angles and clearer virtual image projection, enhancing the overall display quality.
Implementation Method 1
The light flux incident on the incident surface of the light guide body is changed in a traveling direction by diffraction by a diffraction structure of a coupling region in the light guide body. The light flux changed in the traveling direction is emitted from the emission surface after being expanded by being replicated in a first direction corresponding to a horizontal direction of the image visually recognized by the observer due to diffraction by a diffraction structure of an expansion region in the light guide body
Data Source
AI summary
An optical system includes a display that emits a light flux visually recognized by an observer as an image, and a light guide body that replicates the light flux. The light flux is emitted from the emission surface after being expanded by being replicated in a first direction corresponding to a horizontal direction of the image visually recognized by the observer due to diffraction by a diffraction structure of an expansion region in the light guide body, a second direction corresponding to a vertical direction of the image, or both the directions. A coherence length of the light flux diffracted and emitted in the expansion region in the light guide body is smaller than twice a shorter interval between the diffraction structure and each of a front surface and a back surface of the light guide body.