Optical Security Device Diffractive Grating Resolution Clarity
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Solution Overview
Problem
Existing optically variable devices (OVDs) face limitations in displaying high-resolution, three-dimensional imagery on physical substrates, particularly under extended or diffuse light sources, leading to blurring and loss of clarity, especially in regions far from the image plane.
Innovation Solution
The use of a security device comprising a plurality of focusing elements and image elements with diffractive grating or sub-wavelength grating elements, arranged to generate diffraction images observable at various viewing angles, including red, green, and blue sub-elements with distinct grating frequencies and non-diffractive areas to produce high-resolution, true-color, and grayscale images, overcoming previous resolution limitations and lighting issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If surface relief holograms and holographic stereograms are used to display three-dimensional images, then high resolution imagery can be achieved, but blurring and loss of clarity occur when viewed under extended or diffuse light sources
Solution Approach 1:
The image is divided into multiple sub-images, each viewable from a specific angular range. Each sub-image is associated with a focusing element that directs light from that angular range to the corresponding sub-image region, preventing mixing of perspectives under diffuse lighting
Solution Approach 2:
Different regions of the device have specialized properties: focusing elements at specific locations direct light to specific sub-image regions. Each local area is optimized for its specific angular range, maintaining clarity even when overall lighting is diffuse
2Measurement precision
If diffractive OVD imagery is displayed on physical substrates, then high resolution images can be generated, but regions furthest from the image plane suffer from blurring and loss of clarity
Solution Approach 1:
The patent transitions from planar 2D holographic display to a 3D structured display with focusing elements positioned at specific distances from the substrate. This adds a spatial dimension (depth) to the system, allowing light to be focused from multiple angular ranges while maintaining image plane integrity across different viewing distances
3Ease of manufacture
If traditional security printing technologies are used, then documents can be produced, but they are easily copied using color photocopiers and computer scanning equipment
Solution Approach 1:
The device displays different color images or patterns depending on the viewing angle. Under diffuse lighting, each angular range contributes different color information to different sub-image regions, creating a composite effect that changes with perspective and cannot be easily replicated by traditional copiers
Solution Approach 2:
The optical properties of the device are dynamic rather than static. The image characteristics (color, clarity, content) change dynamically based on viewing angle and lighting conditions, making static copying ineffective
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 high-resolution, three-dimensional images that maintain clarity across a range of viewing angles and lighting conditions, enhancing security features on valuable documents like banknotes by providing vibrant, sharp, and accurate representations.
Implementation Method 1
each image element comprises a diffractive grating element or sub-wavelength grating element which when illuminated by a light source generates a diffraction image observable at a range of viewing angles around the device
Implementation Method 2
a plurality of focusing elements; a plurality of image elements associated with each focusing element wherein said image elements include at least a first and a second group of image elements, wherein each image element is located in an object plane to be viewable through the associated focusing element
Data Source
AI summary
A security device is disclosed including a substrate and one or more focusing elements or lens structures located on one side of the substrate. The security device includes a plurality of image elements associated with each focusing element wherein the image elements include at least first and second groups of image elements. Each image element may be composed of pixels located in an object plane to be viewable through the associated focusing element. Each image element comprises a diffractive grating element or sub-wavelength grating element which when illuminated by a light source generates a diffraction image observable at a range of viewing angles around the device. Image elements of the first group are visible in a first range of viewing angles and image elements of the second group are visible in a second range of viewing angles. The security device is particularly suitable for use on security documents, such as banknotes. A method of forming a security device is also disclosed.