Oblique Collimator Channels Block Ambient Light in Optical Fingerprint Sensors
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Solution Overview
Problem
Optical fingerprint identification apparatuses face interference from intense ambient light, such as sunlight, which degrades image quality by transmitting into the image-capture device.
Innovation Solution
A fingerprint identification apparatus featuring a collimator with alternately stacked light-shielding and light-transmitting layers, where the openings of the light-shielding layers are arranged obliquely to form optical channels that block ambient light from reaching the image-capture device, thereby enhancing image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional optical fingerprint identification apparatus is used, then the structure is simple, but ambient light interferes with image-capture quality
Solution Approach 1:
A collimator structure is introduced as an intermediary component between the light-transmitting device and the image-capture device. This collimator includes light-shielding layers with obliquely arranged openings that selectively block ambient light while allowing fingerprint-related light to pass through, thereby improving image-capture quality without fundamentally changing the optical fingerprint identification principle
Solution Approach 2:
The collimator is segmented into multiple light-shielding layers with alternating light-transmitting layers. Each layer contains multiple openings arranged in specific patterns, creating a segmented structure that progressively filters ambient light from different directions while maintaining the passage of useful light signals
2Measurement precision
If the collimator with oblique openings is added to block ambient light, then image-capture quality improves, but device complexity increases
Solution Approach 1:
The collimator serves as a specialized intermediary component that can be added to existing optical fingerprint identification apparatus without replacing the core optical system. It mediates between the light source and image-capture device, providing ambient light rejection while maintaining compatibility with the existing structure
Solution Approach 2:
The openings in the light-shielding layers are arranged in an oblique direction rather than perpendicular to the pressing surface. This dimensional change in opening orientation creates optical channels that exploit angular separation between ambient light and fingerprint light paths, achieving selective light blocking through geometric arrangement
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 effectively prevents ambient light from interfering with the fingerprint information, resulting in improved image-capture quality by directing ambient light away from the sensing mechanism.
Implementation Method 1
The collimator includes a plurality of light-shielding layers and a plurality of light-transmitting layers that are alternately stacked. Each of the light-shielding layers has a plurality of openings respectively corresponding to the plurality of pixel regions. Openings of the plurality of light-shielding layers corresponding to one pixel region are arranged along an oblique direction.
Implementation Method 2
An optical fingerprint identification apparatus can obtain a fingerprint image using the principle of total reflection. The fingerprint is formed by a plurality of irregular ridges (i.e., peaks) and recesses (i.e., valleys). When a finger is pressed on the fingerprint identification apparatus, the peaks of the fingerprint are in contact with a light-transmitting device of the fingerprint identification apparatus
Implementation Method 3
The fingerprint peaks in contact with the light-transmitting device destroy the total reflection of a sensing light beam in the light-transmitting device, and therefore the image-capture device obtains dark lines corresponding to the fingerprint peaks.
Data Source
AI summary
A fingerprint identification apparatus including a light-transmitting device, an image-capture device disposed opposite to the light-transmitting device, and a collimator disposed between the light-transmitting device and the image-capture device is provided. The collimator includes a plurality of light-shielding layers and a plurality of light-transmitting layers that are alternately stacked. Each of the light-shielding layers has a plurality of openings respectively corresponding to a plurality of pixel regions of the image-capture device. Openings of the plurality of light-shielding layers corresponding to one pixel region are arranged along an oblique direction. The oblique direction and a normal direction of a pressing surface of the light-transmitting device have an included angle θ, and 0°<θ<90°.