Biometric Imaging Device with Polarizers for Reflection Reduction
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Solution Overview
Problem
Optical fingerprint sensors under display panels face issues with internal reflections from display layers, which interfere with fingerprint image capture, and rely on display illumination, limiting independent operation and image quality.
Innovation Solution
An optical biometric imaging device with a light source adjacent to the lens assembly, featuring a waveguide for vertical decoupling and rotatable linear polarizers to minimize reflections, allowing controlled illumination and improved image capture without relying on display panel illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If display pixels are used to illuminate the finger during fingerprint image acquisition, then the finger can be illuminated, but light emitted by the display panel is reflected by various layers and reaches the image sensor to disturb the capture
Solution Approach 1:
The patent divides the illumination function from the display function by placing a separate light source adjacent to the lens assembly. This segmentation allows the display to perform its primary function while the dedicated light source provides illumination without generating harmful reflections, as it is positioned to illuminate the finger from the side rather than from above the display panel.
Solution Approach 2:
The patent introduces a polarizer as an intermediary element between the light source and the image sensor. The polarizer filters out reflected light by allowing only light with specific polarization orientation to pass through, thereby eliminating the harmful reflections while maintaining the useful illumination function.
2Adaptability or versatility
If a light source is arranged adjacent to the lens assembly, then independent operation is enabled, but the device complexity increases due to additional optical components
Solution Approach 1:
The patent combines multiple functions into a single integrated assembly. The light source, polarizer, and lens assembly are merged into one compact unit that can be positioned adjacent to the display panel. This merging approach enables independent operation while minimizing the increase in device complexity through integrated design.
Solution Approach 2:
The patent positions the light source in a different spatial dimension relative to the display panel, placing it adjacent to the lens assembly rather than integrated within the display structure. This dimensional repositioning enables independent operation and allows the light source to illuminate the finger without interfering with the display's primary function, while the polarizer handles the reflection filtering in a separate optical path.
3Object-affected harmful factors
If a ring-shaped second linear polarizer is arranged over the light source, then reflections are minimized, but the device complexity increases
Solution Approach 1:
The patent employs a ring-shaped second linear polarizer with an asymmetric geometry that is specifically positioned over the light source. This asymmetric design allows the polarizer to effectively minimize reflections from the display panel while maintaining compatibility with the overall device structure. The ring shape provides targeted polarization filtering where needed without unnecessarily complicating the entire optical system.
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 fingerprint imaging by reducing unwanted reflections and allowing independent operation, improving image quality and user experience by using infrared light and polarizers to filter out direct reflections, thus optimizing optical performance.
Implementation Method 1
the at least one light source comprises a waveguide configured to provide vertical decoupling of light
Implementation Method 2
a first linear polarizer arranged between the light source and the image sensor
Implementation Method 3
a ring-shaped second linear polarizer arranged over the at least one light source to polarize light emitted by the light source in a direction away from the image sensor
Implementation Method 4
a lens assembly comprising at least one lens configured to focus light reflected by a biometric object onto the image sensor
Data Source
AI summary
An optical biometric imaging device includes an image sensor having a plurality of photodetector pixels; a lens assembly having at least one lens configured to focus light reflected by a biometric object onto the image sensor; at least one light source arranged adjacent to the lens assembly and which emits light towards a sensing surface of the biometric imaging device. The at least one light source comprises a waveguide which vertical decouples light; a first linear polarizer arranged between the light source and the image sensor; and a ring-shaped second linear polarizer arranged over the light source to polarize light emitted by the light source in a direction away from the image sensor and having an opening which allows light reflected by a biometric object to reach the lens without being filtered by the second linear polarizer. At least one of the polarizers are rotatable.