VCSEL Biometric Sensor Narrow Spectrum Filtering
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Solution Overview
Problem
Current biometric identification systems face challenges in achieving a high signal-to-noise ratio, especially in outdoor conditions due to varying infrared illumination and thermal shifts, which affect the accuracy and reliability of image recognition.
Innovation Solution
A device utilizing a VCSEL infrared light source with a narrow emission spectrum and an infrared bandpass filter optimized to the peak wavelength of 940 nm, combined with a diffuser unit, to enhance the signal-to-noise ratio by minimizing ambient light interference and maintaining high infrared light intensity across temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a wide bandpass filter is used to account for thermal shifts of IR-LED peak wavelength, then the filter covers the full spectral range, but the signal-to-noise ratio deteriorates because solar illumination noise cannot be sufficiently filtered
Solution Approach 1:
The patent changes the key parameter from filter bandwidth to light source spectral narrowness. By using VCSEL with extremely narrow spectral width (<5nm FWHM) instead of broad-spectrum IR-LED, the system can employ a narrow bandpass filter (10nm bandwidth) that simultaneously blocks solar noise and passes the laser wavelength even with thermal shifts, resolving the contradiction between spectral coverage and signal-to-noise ratio
Solution Approach 2:
The patent substitutes conventional IR-LED illumination with VCSEL (vertical-cavity surface-emitting laser) technology. This replacement provides fundamentally different spectral characteristics - extremely narrow linewidth and high coherence - enabling the use of narrow bandpass filtering to achieve both thermal robustness and high signal-to-noise ratio that is impossible with broad-spectrum LED sources
2Measurement precision
If conventional IR-LED illumination is used, then the system is simple and inexpensive, but the signal-to-noise ratio is insufficient due to broad spectral width and thermal wavelength shifts
Solution Approach 1:
The patent fundamentally changes the spectral parameter of the illumination source from broad (IR-LED: ~36nm FWHM) to extremely narrow (VCSEL: <5nm FWHM, typically 1-3nm). This parameter change enables effective narrow bandpass filtering that achieves high signal-to-noise ratio while maintaining thermal stability, as the narrow VCSEL spectrum remains within the 10nm filter bandwidth even with temperature-induced wavelength shifts
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 significantly improves the signal-to-noise ratio of images taken in outdoor conditions, leading to more secure and reliable biometric identification by reducing noise and maintaining high infrared light intensity, even under varying temperatures.
Implementation Method 1
an infrared light source, wherein the infrared light source is a VCSEL, to provide additional infrared light for the infrared light conditions, and where the VCSEL emits a narrow infrared light spectrum with a peak wavelength of 940 nm
Implementation Method 2
an infrared bandpass filter is arranged in the light path between the object and a sensor array of the optical image sensor element having a transmission window covering at least the peak wavelength of the VCSEL, and wherein the transmission window of the bandpass filter has a width of 10nm
Data Source
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AI summary
The invention describes a device (1) and a method (100) for bio metric identification of an object with a significantly improved signal-to-noise ratio. The device comprises an optical image sensor element (11) at least sensitive to an infrared spectrum to take at least one picture (112) of the object (2) under ambient light conditions (ALC) with additional infrared light conditions (ILC), an infrared light source (12) to provide additional infrared light (IR) for the infrared light conditions (ILC), and a processing unit (13) to provide an image or image code (131) for the bio metric identification obtained from the picture (112), where the infrared light source (12) emits a narrow infrared light spectrum with a peak wavelength (121) between 925nm to 955 nm and with a full width of half maximum of less than 5nm, and where an infrared bandpass filter (14) is arranged in the light path (LP) between the object (2) and a sensor array of the optical image sensor element (11) having a transmission window (141) between 925nm and 955 nm covering at least the peak wavelength (121) of the infrared light source (12).