Graded Waveguide Coating for Uniform Multi-Wavelength Emission
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Solution Overview
Problem
Existing waveguides struggle to provide spatially homogeneous emission with consistent intensity and spectrum across multiple wavelengths, leading to variability in image brightness and quality as viewers move around the viewing window.
Innovation Solution
A waveguide with a graded transmission coating comprising alternating layers of dielectrics with limited discrete thickness changes, optimized for specific wavelengths, such as red, green, and blue, to ensure consistent intensity and spectrum across replicas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional waveguide coating is used, then the manufacturing process is simple, but the emission uniformity and image quality vary across different viewing angles
Solution Approach 1:
The coating is segmented into multiple discrete layers (at least two layers) with different optical properties. Each layer has specific thickness ranges (first layer: 50-200nm, second layer: 200-500nm) and refractive index characteristics that work together to achieve uniform emission across viewing angles, replacing the conventional single homogeneous coating layer
Solution Approach 2:
Different regions of the coating structure have optimized local properties - the first layer has specific thickness (50-200nm) and refractive index suited for certain wavelength ranges, while the second layer has different thickness (200-500nm) and refractive index for complementary wavelengths. This local optimization of each layer's properties achieves global emission uniformity
2Adaptability or versatility
If the waveguide coating is optimized for multiple wavelengths, then the spectrum consistency improves, but the absorption losses increase
Solution Approach 1:
The coating parameters (layer thicknesses and refractive indices) are specifically optimized for multiple wavelengths including red (630-670nm), green (500-540nm), and blue (430-470nm) regions. The first layer thickness of 50-200nm and second layer thickness of 200-500nm create constructive interference patterns across these wavelength ranges, achieving broad spectral consistency while managing absorption through precise parameter control
3Illumination intensity
If the waveguide coating is optimized for specific wavelengths, then the image quality and consistency improve, but the manufacturing precision requirements increase
Solution Approach 1:
Specific parameter ranges are defined to balance performance and manufacturability: first layer thickness 50-200nm, second layer thickness 200-500nm, with refractive index constraints (|n1-n2|>0.4). These parameter specifications achieve image brightness consistency across viewing angles while remaining within achievable manufacturing tolerances for conventional deposition processes
Solution Approach 2:
The coating uses composite dielectric material structures with at least two different materials having distinct refractive indices. This composite approach enables wavelength-selective optical control through the interference effects of layered structures, achieving image quality consistency while using materials that can be deposited with standard manufacturing precision
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 provides spatially homogeneous emission with reduced absorption losses and manufacturing complexity, enhancing image quality and consistency across different viewing angles.
Implementation Method 1
A first surface of the pair of parallel surfaces comprises a plurality of layers of a first dielectric and a plurality of layers of second dielectric arranged in an alternating configuration
Implementation Method 2
A difference in refractive index between the first dielectric and second dielectric is greater than 0.4
Implementation Method 3
Light scattered from an object contains both amplitude and phase information... A waveguide with a graded transmission coating
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
A method of forming a transmission coating for a waveguide. The transmission coating comprises a plurality of layers. The method comprises 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. Then, there is 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.