Asymmetric Surface Relief Microstructures for Broad-Angle Optical Security
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Solution Overview
Problem
Existing optical security elements, such as diffraction gratings and holograms, have a limited angular range of visibility and can be easily replicated, reducing their security effectiveness, and there is a need for alternative optical security elements that provide a distinct color appearance without rainbow colors when illuminated with white light.
Innovation Solution
A surface relief structure with non-periodically arranged grooves and anisotropic lands having asymmetric flanks, which causes anisotropic scattering of light, resulting in a colored appearance that remains consistent over a broad angular range without splitting into rainbow colors, achieved through the combination of scattering and interference effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a periodic diffraction grating is used, then the optical effect is strong and distinct, but the angular range of visibility is narrow
Solution Approach 1:
The patent applies asymmetry by using non-periodic modulation of the diffraction grating parameters (such as groove depth, width, or spacing) across the grating surface. This non-periodic variation causes the diffracted light to be scattered into multiple directions, thereby expanding the angular range of visibility while maintaining the diffraction-based optical effect. The asymmetric structure prevents the formation of a single dominant diffraction angle, distributing the optical effect across a broader viewing cone.
2Adaptability or versatility
If a hologram is used, then the optical appearance is complex and changes with observation angle, but the technology is widely accessible and easy to replicate
Solution Approach 1:
The patent employs a composite structure combining a diffraction grating with an additional optical layer or material that modifies the diffracted light. This could include overlaying the grating with a cholesteric liquid crystal layer, a photonic crystal layer, or a multilayer dielectric coating. The interaction between the diffraction effect and the additional optical properties creates a complex, angle-dependent appearance that is difficult to replicate, thereby enhancing security while maintaining optical variability.
3Adaptability or versatility
If an asymmetric diffraction grating is used, then the rainbow colors appear with different intensities from opposite directions, but the structure requires precise control of asymmetry parameters
Solution Approach 1:
The patent transitions from controlling asymmetry in a single dimension (such as groove depth only) to introducing asymmetry across multiple dimensions simultaneously. This could involve varying groove depth, width, and spacing in a coordinated non-periodic pattern, or adding a temporal dimension through dynamic modulation. By distributing the asymmetry control across multiple parameters and dimensions, the manufacturing complexity of each individual parameter is reduced while maintaining the overall directional optical effect.
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 proposed surface relief structure enhances the angular range of visibility and security by producing a consistent colored optical effect, making it difficult to replicate, thereby increasing the security level of optical security elements.
Implementation Method 1
the scattered light is colored without showing rainbow colors... anisotropic scattering such that the scattered light is colored
Implementation Method 2
Due to a superposition of interference and scattering effects, such surface relief microstructures cause the scattered light to have a distinct and saturated color appearance, without the rainbow colors which typically appear for diffraction gratings
Data Source
Figure 1.1~1.3
Figure 2~3
Figure 4.1~4.4
AI summary
The present invention relates to a surface relief structure for use in optical security elements, which comprises grooves (14) and anisotropic lands (12, 22), wherein the grooves and lands are arranged non-periodically along the preferred scattering axis, the heights of the lands are within one ore more height levels, the upper surfaces of the lands (13, 23), the surfaces of the grooves (14) are flat and substantially parallel to each other and in a cross-section with the preferred scattering plane (9) the flanks (15, 16, 25, 26) of the lands (12, 22) are asymmetric. The invention further relates to methods of making as well as to security elements comprising such relief structures.