Optical Fingerprint Sensor Anti-Spoofing via Polarization and Angular Filtering
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Solution Overview
Problem
Current fingerprint sensors struggle to distinguish between real and spoof fingerprints, especially when high-resolution spoof fingerprints are used, leading to potential unauthorized access to devices and accounts.
Innovation Solution
An optical fingerprint sensor design that utilizes a combination of lenses, apertured baffle-layers, and polarizing elements to detect the angular distribution of electromagnetic energy, with anti-spoof photodiodes positioned between imaging photodiodes to differentiate between real and spoof fingerprints by filtering and correlating larger-angle light with the pattern of illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional image sensors are used for fingerprint sensing, then the device complexity is low and ease of manufacture is good, but the reliability for distinguishing real fingerprints from spoof fingerprints deteriorates
Solution Approach 1:
The image sensor is segmented into multiple functional pixel types: imaging photodiodes for capturing fingerprint images and anti-spoof photodiodes for detecting polarization characteristics. This segmentation allows the system to simultaneously obtain both fingerprint image data and polarization data, improving spoof detection accuracy while maintaining manageable device complexity through modular pixel design
Solution Approach 2:
The patent introduces a new detection dimension by incorporating polarization detection capability alongside traditional intensity-based imaging. Anti-spoof photodiodes with polarizing elements measure the polarization state of light reflected from the fingerprint sample, adding a physical property dimension that helps distinguish real fingerprints from spoofs
2Measurement precision
If multiple photodiodes with different functions are integrated into a single pixel array, then the measurement precision for spoof detection improves, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
Different regions of the pixel array are assigned different functional qualities: imaging photodiodes are optimized for capturing fingerprint images, while anti-spoof photodiodes are configured with polarizing elements to detect polarization. This local differentiation of quality allows each pixel type to perform its specific measurement function with high precision while using the same basic pixel array structure
Solution Approach 2:
The pixel array structure serves multiple functions: it simultaneously captures fingerprint images through imaging photodiodes and detects polarization characteristics through anti-spoof photodiodes. This multi-functionality is achieved by integrating different photodiode types into a single array, allowing one device to perform both imaging and polarization detection without requiring separate systems
3Reliability
If apertured baffle-layers are used to block smaller-angle light, then the reliability for detecting material properties improves, but the loss of energy and productivity decrease
Solution Approach 1:
The patent extracts the polarization detection function from the main imaging path by using separate anti-spoof photodiodes that receive light through different optical paths. The apertured baffle-layers selectively block certain angle ranges of light for imaging photodiodes while allowing polarization-sensitive light to reach anti-spoof photodiodes, separating the two detection functions to minimize energy loss
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
Enhances spoof detection accuracy by providing additional information about the material properties of the fingerprint sample, which can be used in machine learning algorithms to identify spoof fingerprints, thereby improving the reliability of fingerprint authentication.
Implementation Method 1
filtering larger-angle light incident on the plurality of anti-spoof photodiodes to at least one polarization direction, the larger-angle light being electromagnetic energy with incident angle greater than five degrees from the optical axis
Implementation Method 2
blocking smaller-angle light from impinging a plurality of anti-spoof photodiodes of the pixel array, the smaller-angle light being electromagnetic energy with incident angle less than five degrees from an optical axis
Implementation Method 3
controlling a display of an electronic device to output a pattern of light to illuminate a fingerprint sample touching the display near an optical fingerprint sensor
Implementation Method 4
detecting the larger-angle light at the at least one polarization direction using the plurality of anti-spoof photodiodes
Data Source
AI summary
A method for detecting spoof fingerprints detected using an optical fingerprint sensor and polarization includes controlling a display of an electronic device to output a pattern of light to illuminate a fingerprint sample touching the display; blocking smaller-angle light from impinging a plurality of anti-spoof photodiodes of the pixel array; filtering larger-angle light incident on the plurality of anti-spoof photodiodes to at least one polarization direction; detecting the larger-angle light using the plurality of anti-spoof photodiodes; correlating the larger-angle light with the pattern of light; determining the fingerprint spoofing based at least in part on the correlation of the larger-angle light and the pattern of light; and wherein the plurality of anti-spoof photodiodes is interleaved with a plurality of imaging photodiodes such that each anti-spoof photodiode of the plurality of anti-spoof photodiodes is between adjacent imaging photodiodes of the plurality of imaging photodiodes.