Waveguide Transmission Coating with Discrete Thickness Steps
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Solution Overview
Problem
Existing waveguides struggle to provide spatially homogeneous emission with consistent intensity and spectrum across different wavelengths, leading to variability in image brightness and quality as viewers move around the viewing area, and current graded coatings are complex, expensive, and difficult to manufacture reliably.
Innovation Solution
A waveguide with a first surface comprising alternating layers of dielectrics having discrete thickness changes, optimized for specific wavelengths, and a method to adjust coating parameters based on measured deviations to ensure consistent emission, reducing manufacturing complexity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If graded transmission coatings are used to achieve spatially homogeneous emission, then image quality and uniformity are improved, but manufacturing complexity and cost increase significantly
Solution Approach 1:
The patent changes the parameter of coating thickness from continuous graded variation to discrete stepped variation. By using a small number of discrete thickness values (e.g., 3-5 values) instead of continuous grading, the manufacturing complexity is reduced while still achieving substantially homogeneous emission across the waveguide output face.
Solution Approach 2:
The patent applies different discrete thickness values to different regions of the transmission coating. By optimizing the thickness distribution locally across the waveguide face, the coating achieves spatially homogeneous emission characteristics while maintaining manufacturability through a limited set of thickness values.
2Illumination intensity
If continuous thickness variation is used in graded coatings, then emission uniformity is improved, but manufacturing precision and reliability deteriorate
Solution Approach 1:
The patent transforms the continuous thickness parameter into a discrete parameter with a limited number of possible values. This discretization makes the coating process more robust and less sensitive to manufacturing variations, as precise continuous control is replaced by control over a small set of discrete thickness levels.
Solution Approach 2:
The patent accepts that individual coating layers with discrete thickness values may have slight variations, but the overall system achieves uniformity through the statistical averaging effect of multiple layers. This approach is more tolerant of manufacturing imperfections than precise single-layer continuous grading.
3Adaptability or versatility
If multi-wavelength optimization is implemented, then spectral consistency is improved, but coating design complexity increases
Solution Approach 1:
The patent optimizes the discrete thickness values to simultaneously satisfy multiple wavelength requirements. By selecting thickness values from a discrete set that work across different wavelengths, the coating achieves spectral consistency without requiring complex wavelength-specific grading for each wavelength.
Solution Approach 2:
The transmission coating with discrete thickness values is designed to perform multiple functions across different wavelengths simultaneously. The same discrete thickness structure provides homogeneous emission for multiple wavelengths, making the coating universally applicable across the spectral range rather than requiring separate optimized coatings for each wavelength.
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 waveguide achieves spatially homogeneous emission with consistent intensity and spectrum, improving image quality and reducing manufacturing time and cost, particularly suitable for applications like head-up displays.
Implementation Method 1
The waveguide comprises a pair of parallel surfaces arranged to provide waveguiding therebetween
Implementation Method 2
A first surface of the pair of parallel surfaces comprises a plurality of layers of a first dielectric and a plurality of layers of a second dielectric arranged in an alternating configuration
Implementation Method 3
Each layer of the first and second dielectric has a first end and a second end. A percentage change in the thickness of each layer from the first end to the second end of that layer has one of a plurality of discrete values
Data Source
AI summary
A method of forming a multi-layer transmission coating for a waveguide, including a step a of determining a first coating parameter and a coating function for each layer to optimise the transmissivity at a plurality of locations along the waveguide for a plurality of different wavelengths. The coating function is chosen from a plurality of allowable coating functions. Next, there is a step b of forming the plurality of layers using the determined coating parameters and coating functions, and a step c of measuring a thickness of at least one layer at each of the plurality of locations. The measurements indicate that the coating function deviates from that selected during the optimisation of step a. Finally, there is a step d of determining a second coating parameter for at least one layer by repeating the optimisation of step a using the coating function derived from the measurements of step c.