Optical Security Device With Reflective Polarizer
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Solution Overview
Problem
Current optical security elements, while providing a high level of security, lack distinctive features for forgery protection and are limited in observation modes, particularly when fixed on substrates that prevent transmission viewing.
Innovation Solution
Incorporating a reflective polarizer between two patterned retarders with zonewise different optical axis orientations, allowing for observation in both reflection and transmission modes, and enabling the encoding and decoding of images with polarized light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a traditional transmissive optical security element is used, then the encoded information is visible when viewed through the element, but the device cannot be observed when fixed on a substrate that prevents transmission viewing
Solution Approach 1:
The optical security device is designed to function in multiple observation modes (reflection and transmission) by incorporating a reflective polarizer between two patterned retarders. This allows the same device to be viewed both when fixed on a substrate (reflection mode) and when removed (transmission mode), making it universally applicable regardless of mounting conditions.
Solution Approach 2:
The invention adds a new dimension to observation by enabling both reflection and transmission viewing modes. The reflective polarizer creates a reflection path that works when the device is mounted on a substrate, while the transmission path remains available when removed, effectively adding a temporal dimension to the observation capability.
2Adaptability or versatility
If a reflective polarizer is incorporated between two patterned retarders, then the device enables observation in both reflection and transmission modes, but the device complexity increases
Solution Approach 1:
The reflective polarizer serves multiple functions simultaneously: it acts as a polarizing element for the transmission mode and as a reflective element for the reflection mode. This multi-functionality justifies the increased structural complexity by enabling versatile observation capabilities in both mounted and unmounted states.
3Loss of information
If patterned retarders with zonewise different optical axis orientations are used, then encoded information becomes visible with polarized light analysis, but the manufacturing precision requirements increase
Solution Approach 1:
The patterned retarders are designed with zonewise different optical axis orientations, where different regions have specifically tailored optical properties. This local quality variation encodes the security information spatially, allowing the information to be visible only when analyzed with polarized light, thereby securing the information while managing manufacturing precision through localized control.
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 solution enhances security by enabling unique observation modes, ensuring that encoded information can be viewed both when the device is fixed on a substrate and after removal, with improved visibility and contrast through polarized light analysis.
Implementation Method 1
a reflective polarizer is between the two retarders, the polarizing area overlapping at least with a part of each retarder
Implementation Method 2
a first and a second optical retarder layer each with zonewise different orientation of the optical axis
Data Source
AI summary
The invention relates to an optical device comprising two patterned retarders and a reflective polarizer between the retarders. Information which is stored in the pattern of the retarders can be observed both in transmission and reflection. The device according to the invention can be used as high security element, for example for banknotes.