Light Guide Layer for Optical Fingerprint Imaging
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Solution Overview
Problem
Current systems for direct optical recording of skin prints, especially for FBI-standard quality, face challenges in maintaining high spatial resolution and contrast due to the need for additional optical elements and increased thickness, which complicates production and increases costs, while also compromising display quality.
Innovation Solution
A mobile device apparatus with a light guide layer and adhesion layers that allow directed light coupling for total internal reflection at the skin surface, enabling high spatial resolution without compromising the display layer's functionality, using LEDs for light in-coupling and out-coupling structures that adjust angles and refractive indices to achieve efficient illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional optical elements are integrated to achieve directed light coupling for total internal reflection, then illumination quality and spatial resolution are improved, but device thickness increases and production complexity increases
Solution Approach 1:
The patent combines the light guide layer with the display layer into a single integrated structure. The light guide layer is positioned directly beneath the display layer and uses the display layer's front surface as the placement surface, eliminating the need for separate optical elements and reducing production complexity while maintaining illumination quality and spatial resolution through total internal reflection.
Solution Approach 2:
The display layer serves multiple functions: it acts as both the display element and the placement surface for fingerprint capture. The light guide layer simultaneously provides illumination and enables total internal reflection for high-resolution imaging. This multi-functionality reduces the number of components needed and simplifies the overall device structure.
2Strength
If the terminating layer thickness is increased to improve display quality, then display functionality is enhanced, but spatial resolution and contrast of skin prints decrease
Solution Approach 1:
The patent uses total internal reflection to dynamically control light propagation. By positioning the light guide layer directly beneath the display layer and utilizing the refractive index difference at the air-skin interface, the system achieves high spatial resolution regardless of the display layer thickness. The light is reflected back through the display layer, maintaining both display quality and imaging resolution.
3Adaptability or versatility
If a separate optical sensor layer is added to read security documents, then document reading capability is improved, but equipment costs and device complexity increase
Solution Approach 1:
The display layer is designed to serve dual purposes: displaying information and capturing images of security documents. The light guide layer provides illumination for both fingerprint capture and document imaging. This multi-functional design eliminates the need for separate optical sensor layers, reducing equipment costs and device complexity while maintaining document reading capability.
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 allows for high-quality skin print recording that meets FBI standards without degrading spatial resolution or display quality, using a compact design that improves image clarity and reduces production complexity and costs.
Implementation Method 1
directed light coupling for total internal reflection at the skin surface
Implementation Method 2
out-coupling structures that adjust angles and refractive indices
Implementation Method 3
using LEDs for light in-coupling
Data Source
AI summary
An apparatus for direct optical recording of skin prints has a display below the placement surface and a light guide layer below the display. The light guide layer has light in-coupling at a narrow side and light out-coupling structures in the surface. By means of angles ε of the light out-coupling structures and differences in the refractive indices of the neighboring layers, a directed coupling out of light occurs in the direction of the placement surface causing a total internal reflection at the placement surface. The display has a transparency of at least 1% of the coupled out light. A first and second adhesion layers are between the display and the light guide layer and between the light guide layer and the sensor layer. The refractive indices of the adhesion layers are at least 1% to 30% lower than those of light guide layer, the display and the sensor layer.