Achromatic Polarization Volume Grating for Wide-Angle RGB Diffraction
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Solution Overview
Problem
Polarization volume gratings face challenges such as high diffraction differentiation between polarizations, back-coupling issues, and high manufacturing costs in near-eye display systems, particularly in handling lights within visible wavelengths and various angles with a single monolithic grating.
Innovation Solution
A multivariable optimization algorithm is applied to derive parameters for a polarization volume grating with multiple layers, optimizing thickness, twist angles, and period to enhance diffraction efficiency, allowing for efficient handling of RGB lights across different angles and wavelengths using a merit function like ƒk(d1,ϕ1,d2,ϕ2,...,dm,ϕm,d)=[1−η1(θ,ψ)]2, where m represents the number of layers, and η1(θ,ψ) is the first-order diffraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single monolithic polarization volume grating is used, then the device complexity is reduced, but the diffraction efficiency varies significantly with wavelength and angle
Solution Approach 1:
The patent divides the single monolithic grating into multiple layered gratings, each layer with optimized parameters for specific wavelength ranges and angles. This segmentation allows each layer to handle specific portions of the spectrum and angular ranges, achieving high diffraction efficiency across the entire visible spectrum while maintaining a relatively compact integrated structure.
Solution Approach 2:
Each layer of the polarization volume grating is designed with locally optimized parameters including period, thickness, and orientation angle, which are specifically tailored to achieve high diffraction efficiency for particular wavelength ranges and incident angles. This local optimization ensures that different regions of the grating structure contribute differently to the overall performance, enabling achromatic operation across wide angular bandwidths.
2Manufacturing precision
If the grating parameters are optimized for a specific wavelength, then the diffraction efficiency at that wavelength is maximized, but the performance degrades at other wavelengths and angles
Solution Approach 1:
The patent systematically varies key parameters including the period, thickness, and orientation angle across multiple layers of the polarization volume grating. By creating a gradient or stepped variation of these parameters from one layer to another, the grating achieves high diffraction efficiency across a broad spectrum of wavelengths and angles, transforming a single-wavelength optimized device into a multi-wavelength achromatic grating.
Solution Approach 2:
The patent employs composite structures combining multiple layers of polarization volume gratings with different parameter sets. Each layer acts as a specialized component optimized for specific conditions, and their composite arrangement enables the overall system to handle a wide range of wavelengths and angles with high efficiency, similar to how composite materials combine different material properties to achieve superior overall performance.
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 high diffraction efficiency across a wide range of wavelengths and angles, reducing the need for multiple gratings and improving color and brightness uniformity, with average efficiencies up to 93.3% for RGB lights, and can be used as both input and output coupler gratings in near-eye display systems.
Implementation Method 1
Bragg polarization gratings for wide angular bandwidth and high efficiency at steep deflection angles
Implementation Method 2
Nanoscale liquid crystal polymer Bragg polarization gratings
Data Source
AI summary
A polarization volume grating, an optical waveguide system and an electronic device are disclosed. Parameters of the polarization volume grating satisfy with those derived by performing a multivariable optimization algorithm on a merit function of ƒk(d1,ϕ1,d2,ϕ2, . . . , dm,ϕm,d)=[1−η1(θ,ψ)]2, wherein the parameters include d1,ϕ1,d2,ϕ2, . . . , dm,ϕm, where m=1, 2, 3, . . . , and d, m is the number of layers of the polarization volume grating, dm is a thickness of mth layer, ϕm is a twist angle in mth layer, and d is a period of the polarization volume grating, k represents a central wavelength on which the multivariable optimization algorithm is performed, θ represents a polar angle of an incident light, ψ represents an azimuth angle of the incident light, and η1(θ,ψ) represents a first-order diffraction efficiency of the polarization volume grating.