Optical See-Through Display Multilayer Gratings for Efficient Out-Coupling
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Solution Overview
Problem
Existing see-through displays suffer from low out-coupling efficiency, non-uniform brightness, and reduced transparency, leading to decreased image quality and user experience, particularly in wearable devices and vehicles.
Innovation Solution
A multilayer grating structure is employed, with spatially varying out-coupling efficiency and enhanced white balance, utilizing metal oxide layers to minimize diffraction of transmissive light and maintain high transparency, manufactured through nanoimprinting technology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single grating is used for out-coupling light, then the device structure is simple, but the out-coupling efficiency is low
Solution Approach 1:
The out-coupling grating is divided into multiple separate gratings (first grating and second grating) with different grating periods. Each grating is responsible for diffracting light of specific wavelengths, thereby increasing the overall out-coupling efficiency while maintaining manageable structural complexity
Solution Approach 2:
The patent introduces a new dimension of differentiation by using gratings with different grating periods (spatial frequency) rather than varying the orientation or position. This allows multiple gratings to coexist without overlapping diffraction patterns while collectively improving out-coupling efficiency across different wavelength ranges
2Object-affected harmful factors
If multiple gratings with different orientations are used, then the rainbow effect is reduced, but the device complexity increases
Solution Approach 1:
Each grating is assigned a specific local function based on its grating period: the first grating handles specific wavelength ranges while the second grating handles complementary wavelength ranges. This local specialization reduces the rainbow effect by ensuring each grating operates in its optimal wavelength band without creating overlapping spectral artifacts
Solution Approach 2:
Instead of varying grating orientations in different planes, the patent uses gratings with different grating periods (spatial frequency dimension) to achieve wavelength-selective diffraction. This approach reduces the rainbow effect while maintaining a simpler two-dimensional grating structure compared to multi-orientation configurations
3Productivity
If a metallic layer is added to the out-coupling grating, then the out-coupling efficiency is enhanced, but the transparency of the grating is reduced
Solution Approach 1:
The patent changes the material parameter of the gratings by using transparent materials with high refractive indices (such as metal oxides like TiO2, SiO2, or Nb2O5) instead of traditional metallic layers. This parameter change allows the gratings to maintain high out-coupling efficiency through strong light-matter interaction while preserving optical transparency for see-through display functionality
4Productivity
If the grating diffracts more light to non-zero transmission orders, then the out-coupling efficiency is improved, but the transparency of the display is reduced
Solution Approach 1:
Each grating is designed with specific local diffraction characteristics tailored to its wavelength range. The first grating diffracts light primarily in reflection direction for its assigned wavelengths, while the second grating does the same for complementary wavelengths. This local optimization ensures high out-coupling efficiency for displayed light while minimizing diffraction of transmissive light, thereby preserving transparency
Solution Approach 2:
The patent uses gratings with different grating periods to differentiate their diffraction behavior across wavelength ranges. This allows each grating to be optimized for reflecting/diffracting its specific wavelength band while having minimal impact on other wavelengths, thereby maintaining overall transparency while improving out-coupling efficiency for the intended display wavelengths
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 multilayer grating structure significantly enhances out-coupling efficiency, maintains high transparency, and improves image quality, reducing power requirements and increasing consumer acceptance in wearable devices.
Implementation Method 1
a diffractive out-coupling grating structure arranged on the transparent substrate for coupling the in-coupled light out from the transparent substrate
Implementation Method 2
The diffractive out-coupling structure comprises at least two multi-layer gratings superimposed on top of each other
Implementation Method 3
multilayer gratings are such that they do not substantially diffract transmissive light, i.e., where the layers interact so as to minimize diffraction to non-zero diffraction orders
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 2D
AI summary
The invention relates to an optical see-through display element and a display device using such element. The element comprises a transparent substrate (10) comprising two opposite faces, an in-coupling structure (12) for coupling light into the substrate, and a diffractive outcoupling grating structure (14, 16) arranged on the transparent substrate for displaying the incoupled light on the transparent substrate. According to the invention, the diffractive outcoupling structure (14, 16) comprises at least two multi-layer gratings superimposed on top of each other on at least one of said opposite faces of the substrate. In particular, multilayer gratings reducing diffraction of transmissive light can be used. The invention helps to increase the out-coupling efficiency of diffractive displays and provides also technology to simultaneously maintain high image quality and transparency.