Variable Refractive Index Diffraction Grating for Compact Near-Eye Displays
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Solution Overview
Problem
Conventional near-eye displays face challenges in achieving a small form factor, large field of view, and large eyebox due to the need for heavy and expensive components, which complicates the design of compact, lightweight systems with two-dimensional expansion and wide field-of-view capabilities.
Innovation Solution
The development of an optical device with a variable refractive index, achieved by depositing and mixing materials with different refractive indices using an inkjet process, forming a diffraction grating with a varying refractive index that provides angular selectivity and reduces the residual layer, allowing for a compact and efficient near-eye display system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional methods are used to satisfy total internal reflection and first-order diffraction conditions, then the display achieves required optical performance, but the system becomes heavy and expensive
Solution Approach 1:
The patent changes the refractive index parameter of the diffraction grating by incorporating high refractive index materials (such as TiO2, HfO2, GaP, GaS, or GaN nanoparticles) into the grating structure. This parameter change enables the grating to achieve the required diffraction efficiency and optical performance while using lighter-weight materials and thinner structures compared to conventional approaches, thereby reducing overall system weight.
Solution Approach 2:
The patent employs composite materials by combining a resin matrix with high refractive index nanoparticles (TiO2, HfO2, GaP, GaS, or GaN) to create a diffraction grating with enhanced optical properties. This composite structure achieves the necessary refractive index variation for effective light diffraction while maintaining a lightweight profile, avoiding the need for heavy conventional optical components.
2Adaptability or versatility
If two different output grating elements are used for two-dimensional expansion, then the display achieves expanded field of view, but the form factor increases
Solution Approach 1:
The patent merges the functions of multiple output grating elements into a single diffraction grating structure by implementing a variable refractive index across the grating. This allows different regions of the same grating to perform the functions that would traditionally require separate grating elements, achieving two-dimensional field of view expansion while maintaining a compact form factor.
Solution Approach 2:
The patent applies local quality by varying the refractive index at different locations within the diffraction grating. By spatially modulating the refractive index (using gradients or discrete variations), the grating can direct light to different angular positions for two-dimensional field of view expansion, with each local region optimized for its specific function, all within a single compact structure.
3Reliability
If heavy and expensive components are used to satisfy optical conditions, then the display achieves required performance, but the system complexity increases
Solution Approach 1:
The patent makes the diffraction grating multi-functional by enabling it to simultaneously satisfy total internal reflection conditions and first-order diffraction conditions through its variable refractive index design. This single component performs multiple optical functions that would traditionally require separate components, reducing system complexity while maintaining required optical performance.
Solution Approach 2:
By changing the refractive index parameter spatially within the diffraction grating, the patent enables a single component to achieve multiple optical functions. The variable refractive index allows the grating to control light in different ways across its structure, replacing multiple specialized components with one versatile element and thereby reducing system 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
This solution enables the creation of near-eye displays with a small form factor, large field of view, and eyebox, enhancing user experience by optimizing light distribution and reducing the weight of the VR/AR system through the use of a diffraction grating with a variable refractive index.
Implementation Method 1
an existence of a first-order diffraction caused by a diffraction grating
Implementation Method 2
an occurrence of total internal reflection of image light coupled into a waveguide
Data Source
AI summary
An inkjet is used to fabricate an optical device having a varying refractive index. The inkjet deposits a first material having a first refractive index and a second material having a second refractive index in a pattern on a substrate. The first material and/or the second material are processed to form an optical device having a refractive index that varies in one or two dimensions. The optical device is used in a virtual-reality system or augmented-reality system to provide angular selectivity from display to a user's eye.