Security Document Optical Waveguide with Embedded Couplers
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Solution Overview
Problem
Current security documents, such as banknotes and passports, despite having advanced security features like volume or surface holograms, can still be counterfeited with sufficient effort, necessitating enhanced security measures.
Innovation Solution
Incorporating an optical waveguide with couplers into the substrate of security documents, allowing light to be coupled in and out, and optionally using luminescent dyes or refractive index layers to enhance visibility and security, making counterfeiting more difficult.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If volume or surface holograms or refractive gratings are used as security features, then the security document becomes harder to counterfeit, but they can still be imitated if sufficient efforts are undertaken
Solution Approach 1:
The optical waveguide is embedded within the substrate structure, creating a nested configuration where the waveguide core is surrounded by cladding layers that are integrated into the substrate. This nesting approach increases security by embedding the security feature within the document structure, making it more difficult to remove or replicate compared to surface-level holograms.
Solution Approach 2:
The waveguide is constructed using composite material layers with different refractive indices (core layer with higher refractive index, cladding layers with lower refractive indices). This composite structure creates optical properties that are difficult to replicate and integrates multiple material functions within a single security feature element.
2Reliability
If an optical waveguide is embedded in the substrate, then manufacturing security is increased, but manufacturing difficulty increases
Solution Approach 1:
The waveguide is divided into distinct functional segments: input coupler region, waveguide core section, and output coupler region. This segmentation allows each part to be optimized and manufactured separately using appropriate techniques, then integrated into the substrate, reducing overall manufacturing complexity while maintaining security.
Solution Approach 2:
The cladding layers serve as intermediary elements between the waveguide core and the substrate environment. These intermediate layers facilitate the integration of the waveguide into the substrate by providing refractive index matching and mechanical coupling, simplifying the overall manufacturing process.
3Reliability
If the substrate is non-transparent, then the coupler can be protected by the substrate, but light coupling and observation becomes more difficult
Solution Approach 1:
The substrate is segmented into transparent window regions and non-transparent protective regions. The transparent windows provide access points for light coupling and observation, while the non-transparent portions protect the couplers. This segmentation allows both protection and operational accessibility to coexist.
Solution Approach 2:
Transparent window regions are extracted from the otherwise non-transparent substrate to create localized access points. These extracted transparent areas allow light to pass through for coupling into and out of the waveguide, while the surrounding non-transparent substrate maintains protective coverage over the coupler structures.
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 optical waveguide and coupler system significantly increases the security of documents by making it harder to manufacture and replicate, while luminescent dyes and refractive index layers enhance visibility and authenticity verification.
Implementation Method 1
The waveguide comprises at least a coupler structured and adapted for coupling light into the waveguide and/or for coupling light out from the waveguide
Implementation Method 2
If the waveguide comprises a first and a second layer, with the first layer having a refractive index higher than the second layer, the first layer can be used to guide the optical waves
Implementation Method 3
the second layer serves to isolate the guided wave from the surroundings. In particular, the second layer can be arranged between the first layer and the substrate, thereby preventing said wave to be absorbed or scattered by the substrate
Implementation Method 4
the document comprises a luminescent dye arranged in or on the waveguide, which dye is luminescent under irradiation of light, e.g. light guided by the waveguide, such that the dye can be used for visualizing the presence of light in the waveguide
Data Source
AI summary
A security document comprises a substrate (1) and an optical waveguide (7). Couplers (10a, 10b) are provided in the waveguide (7) for coupling light into and out of the waveguide. The couplers (10a, 10b) can e.g. by gratings, scattering objects, holograms, luminescent dyes or perforations. The authenticity of the document can be verified using methods based on the properties of the waveguide.