Optical Security Component with Resonant Grating for Polychromatic Imaging
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Solution Overview
Problem
Existing optical security components struggle to produce high-quality colored images under spatially coherent polychromatic lighting without requiring multiple monochromatic sources or filters, and suffer from unwanted color blends due to sensitivity to multiple wavelengths.
Innovation Solution
An optical security component comprising a first layer of dielectric material with a structured pattern forming a computer-synthesized hologram, a second layer with a periodic grating producing a resonant filter, and a third layer encapsulating the structure, which enhances wavelength selectivity and allows for the generation of recognizable images in the visible spectrum under polychromatic lighting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a diffractive optical element is illuminated with polychromatic light, then the optical component can be used with simple lighting, but unwanted color blends occur due to sensitivity to multiple wavelengths
Solution Approach 1:
The patent divides the diffractive optical element into multiple wavelength-specific diffractive structures, each calculated for a specific wavelength. This segmentation allows each structure to handle a narrow spectral band, reducing unwanted color blends while maintaining compatibility with polychromatic light sources.
Solution Approach 2:
Different regions of the diffractive optical element have different local properties - each region contains diffractive structures optimized for specific wavelength bands. This local optimization ensures that each area contributes only its intended color to the overall image, preventing color contamination from other wavelength bands.
2Manufacturing precision
If multiple monochromatic sources or spectral filters are used to achieve high-quality colored images, then color accuracy improves, but device complexity increases
Solution Approach 1:
The diffractive optical element is designed to perform multiple functions simultaneously - it acts as both the image generator and the wavelength selector. The single component replaces what would otherwise require multiple monochromatic sources or complex filter systems, achieving high color quality without increasing device complexity.
Solution Approach 2:
The patent uses computer-synthesized hologram techniques to create diffractive structures that mathematically encode the desired optical behavior. This computational approach allows precise control over wavelength-specific diffraction patterns without requiring physical prototypes or complex experimental setups.
3Manufacturing precision
If diffractive structures are calculated for specific wavelengths, then wavelength selectivity improves, but the component requires monochromatic lighting which reduces ease of use
Solution Approach 1:
The diffractive optical element is segmented into multiple wavelength-specific zones, each containing diffractive structures calculated for a particular wavelength band. This segmentation enables the component to maintain high wavelength selectivity for each band while collectively responding to broad-spectrum polychromatic light, eliminating the need for monochromatic sources.
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
Enables the creation of high-quality, multi-color images or animations without the need for specific lighting devices, offering improved authentication and resistance to counterfeiting by utilizing sub-wavelength gratings and resonant filters to enhance spectral selectivity and color variability.
Implementation Method 1
a second pattern, which is a periodic grating with a period between 100 nm and 700 nm, determined to produce, after deposition of the second layer and encapsulation of said first structure by the third layer, a resonant filter in a first spectral band
Implementation Method 2
the first pattern is adapted to form a first computer-synthesized hologram (HSO) type diffractive element
Implementation Method 3
a first layer of dielectric material, at least partially structured on one face, and having a first refractive index; a third layer of dielectric material, deposited on said second layer, and having a third refractive index
Implementation Method 4
a second layer, deposited on the at least partially structured face of said first layer in at least a first region, and having a spectral band of reflection in the visible
Data Source
AI summary
According to one aspect, the present description relates to an optical security component (20) comprising a first layer (23) made of dielectric material at least partially structured on one side, a second layer (22) deposited on said at least partially structured side in at least one first region and having a spectral band of reflection in the visible, and a third layer (21) made of dielectric material, this third layer being deposited on said second layer. The first layer (23) has, in the first region, at least one first structure (S) formed by a first pattern (S1) that is modulated by a second pattern (S2), said patterns being such that the first pattern forms a first diffractive element of the computer-synthesized-hologram type generating a first recognisable image in at least one first reconstruction plane, and the second pattern is a periodic grating of period comprised between 100 nm and 700 nm producing a resonant filter in a first spectral band.