Optical Fingerprint Imaging Device Stray Light Control
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Solution Overview
Problem
Existing optical biometric devices face challenges in achieving high uniformity and contrast in biometric images due to limited mechanism size, leading to the occurrence of stray light spots.
Innovation Solution
The optical fingerprint imaging device incorporates a light shielding element between the imaging module and light emitting elements, arranged to satisfy specific geometric conditions, reducing stray light spots and enabling a wide imaging area range with high uniform brightness and contrast in a small-sized mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a light shielding element is added to reduce stray light spots, then image contrast and uniformity are improved, but device complexity increases
Solution Approach 1:
A light shielding element is introduced as an intermediary component positioned between the imaging module and light emitting elements. This mediator blocks stray light paths without requiring fundamental changes to the existing imaging or lighting systems, thereby improving image contrast and uniformity while adding minimal complexity.
Solution Approach 2:
The light shielding element extends in the vertical dimension (height direction) rather than requiring lateral expansion. By utilizing the z-axis dimension with a height H satisfying h≤H≤h+(R/tan(θ/2)), the patent effectively blocks stray light without increasing the lateral footprint of the device, maintaining compactness while improving imaging quality.
2Volume of moving object
If the mechanism size is reduced to make the device compact, then device portability is improved, but stray light spots increase
Solution Approach 1:
The patent addresses stray light control in the vertical dimension rather than requiring lateral spacing. The light shielding element's height H is optimized according to h≤H≤h+(R/tan(θ/2)), enabling effective stray light blocking within a compact lateral footprint, thus maintaining small device size while eliminating stray light spots.
Solution Approach 2:
The light shielding element is positioned in advance to preemptively block stray light before it can reach the imaging module. By placing the shielding element between the light emitting elements and imaging module, stray light paths are intercepted beforehand, preventing contamination of the captured image even in compact configurations.
3Area of stationary object
If the imaging area range is expanded, then device functionality is improved, but device complexity increases
Solution Approach 1:
The patent optimizes geometric parameters of the light shielding element, specifically its height H and horizontal distance R from the imaging module center. By satisfying the conditional expression h≤H≤h+(R/tan(θ/2)), the shielding element effectively blocks stray light across a wide imaging area without requiring complex multi-element shielding structures, thus expanding functionality while controlling complexity.
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 arrangement effectively minimizes stray light spots, allowing for high uniform brightness and contrast, thereby enhancing the optical sensing capabilities of the device within a compact design.
Implementation Method 1
the light shielding element is disposed between the imaging module and the at least one light emitting element
Implementation Method 2
the at least one light emitting element is a light emitting diode, a laser diode, or a vertical-cavity surface-emitting laser
Implementation Method 3
a haze of the pressing substrate is less than 5%
Data Source
AI summary
An optical fingerprint imaging device, including a substrate, an imaging module, at least one light emitting element, a light shielding element, a case, and a pressing substrate, is provided. The light shielding element is disposed between the imaging module and the light emitting element. The optical fingerprint imaging device satisfies conditional expressions, h≤H≤h+(R/tan(θ/2)) and Ravg<S<5Ravg, where h is a height from a field angle origin of the imaging module to the substrate, H is a height of the light shielding element at a measurement position, R is a distance from a center of the imaging module to the measurement position, θ is an angle of a field angle of the imaging module, Ravg is an average value of distances from the center to measurement positions of the light shielding element, and S is a distance from the center to a center of the light emitting element.