Interlaced Diffraction Gratings for Rotation-Based Security Image Switching
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Solution Overview
Problem
Conventional diffraction gratings exhibit a second diffraction order with significantly reduced brightness when rotated, leading to an undesirable replay of the same effect, which is undesirable for optically variable security devices.
Innovation Solution
An optical device with interlaced first and second grating regions, where the second grating regions have smaller pitches to ensure a second image dominates the appearance at a second viewing angle, masking the first image, utilizing first and second order diffraction effects to create a seamless image switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional diffraction gratings are used to produce optically variable effects, then the device exhibits diffractive effects at natural viewing angles, but a second diffraction order replays the same effect with significantly reduced brightness when rotated, which is undesirable
Solution Approach 1:
The diffraction grating is divided into multiple zones with different pitch values. The first zone has a pitch that produces a first diffraction order at natural viewing angles, while the second zone has a different pitch that produces a second diffraction order at the same viewing angles. This segmentation allows the harmful second order replay to be spatially separated and controlled, preventing it from appearing as an unwanted duplicate image.
Solution Approach 2:
Different regions of the diffraction grating are assigned different local properties (different pitch values). The first zone is optimized for producing the primary diffractive effect at natural viewing angles, while the second zone is optimized to produce the second diffraction order at the same angles but with different characteristics. This local differentiation ensures that the second order does not replay the same effect but instead creates a complementary or contrasting effect that prevents false authentication.
2Ease of operation
If the diffraction grating is designed to exhibit effects at natural viewing angles, then the device is easy to view and authenticate, but the second diffraction order creates an unwanted replay that complicates the optical effect
Solution Approach 1:
The diffraction grating is divided into multiple zones with different pitch values. The first zone has a pitch that produces a first diffraction order at natural viewing angles, while the second zone has a different pitch that produces a second diffraction order at the same viewing angles. This segmentation allows the harmful second order replay to be spatially separated and controlled, preventing it from appearing as an unwanted duplicate image.
Solution Approach 2:
The pitch parameter of the diffraction grating is varied across different zones. By changing the pitch value from the first zone to the second zone, the diffraction angles and orders are controlled to produce the desired optical effects. This parameter variation allows the device to maintain simplicity at natural viewing angles while managing the complexity of second order effects.
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 device provides a secure authentication mechanism by ensuring the second image conceals or dominates the first image at the second viewing angle, preventing easy duplication and enhancing security through a natural rotation-based image transition.
Implementation Method 1
When white light is incident upon a diffraction grating, it is split into its constituent wavelengths (i.e. colours) according to the diffraction grating equation
Implementation Method 2
the second grating elements having one or more second grating pitches smaller than the one or more first grating pitches such that upon illumination the second grating elements exhibit a first order diffractive effect substantially at the second viewing angle
Data Source
AI summary
An optical device that exhibits a variable optical effect upon illumination is provided. The optical device comprises a set of first grating regions, wherein each first grating region comprises a plurality of first grating elements. The first grating elements have one or more first grating pitches such that upon illumination the first grating elements exhibit at least a first order diffractive effect at a first viewing angle and a second order diffractive effect at a second viewing angle. The optical device further comprises a set of second grating regions, wherein each second grating region comprises a plurality of second grating elements, the second grating elements having one or more second grating pitches smaller than the one or more first grating pitches such that upon illumination the second grating elements exhibit a first order diffractive effect substantially at the second viewing angle. The set of first grating regions is interlaced with the set of second grating regions. The first grating elements are arranged in accordance with a first image and the second grating elements are arranged in accordance with a second image, such that a user viewing the device perceives the first image at the first viewing angle and perceives the second image at least partially overlapping the first image at the second viewing angle.