Thin Optical Fingerprint Sensor Prism Design
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Solution Overview
Problem
Conventional optical fingerprint image acquisition devices are bulky and cannot be effectively integrated into compact electronic devices due to their volume constraints, despite previous attempts to reduce size, which have resulted in insufficient performance for modern applications.
Innovation Solution
A thin type optical fingerprint sensor design featuring a light source on the basal plane of an optical prism, where light rays are reflected by a mirror surface to an image sensing unit, reducing the device's volume and increasing resolution, with a flexible circuit board and LED luminous elements arranged to optimize light refraction within the critical angle for total reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the prism volume is reduced to fit compact electronic devices, then the device can be integrated into compact electronics, but the fingerprint collection area and image resolution deteriorate
Solution Approach 1:
The patent repositions the light source from the lateral side to the basal plane of the prism, utilizing the vertical dimension (thickness direction) for light entry. This dimensional reconfiguration allows the optical path to be folded within the prism's thickness, enabling compact integration while preserving the fingerprint collection area on the collection surface and maintaining image resolution through optimized light reflection geometry.
Solution Approach 2:
The patent inverts the conventional optical path arrangement by having light enter through the basal plane (bottom) rather than the lateral side, and use the mirror surface to reflect light back through the prism to the image sensor. This inverted configuration allows the collection surface to remain on the top face while achieving compact footprint by utilizing the prism thickness for the optical path.
2Length of moving object
If the prism thickness is reduced, then the sensor becomes thinner for compact devices, but the light path length and image quality deteriorate
Solution Approach 1:
The patent utilizes the lateral dimensions of the basal plane for light source arrangement, allowing sufficient light path length within the reduced thickness. The mirror surface is positioned to reflect light at optimal angles, ensuring that even in a thin prism, the light travels an adequate path length through the fingerprint collection zone to maintain image quality and reliability.
Solution Approach 2:
The patent optimizes the mirror surface angle and light source position parameters to achieve effective light reflection within the reduced prism thickness. By carefully adjusting these geometric parameters, the light path length through the fingerprint zone is maximized within the constrained thickness, maintaining image quality while achieving thinness for compact device integration.
3Area of stationary object
If the collection surface area is increased for better fingerprint acquisition, then the fingerprint recognition quality improves, but the device volume increases
Solution Approach 1:
The patent positions the light source on the basal plane, utilizing the thickness dimension for light entry and the mirror surface for light reflection. This allows the collection surface area on the top face to be maximized for better fingerprint acquisition, while the sensor volume remains compact because the optical path is folded within the prism thickness rather than extending laterally.
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 design achieves a thinner fingerprint sensor with a larger collection area, allowing for effective use in various devices, reducing the prism's thickness to a quarter of the collection surface width while enhancing image resolution.
Implementation Method 1
light rays emitted from the light source enter the optical prism through the basal plane, and are reflected by a fingerprint put on the collection surface to form an image beam, the image beam being reflected by the mirror surface
Implementation Method 2
light sources of luminous elements are input through the basal plane of the prism and irradiated onto the fingerprint, and light rays are reflected by a mirror surface of the optical prism
Implementation Method 3
arranged to optimize light refraction within the critical angle for total reflection
Data Source
AI summary
A thin optical fingerprint sensor, including: a shell; an optical prism arranged in the shell with a collection surface arranged on the top of the optical prism, a basal plane corresponding to the collection surface and situated on the bottom of the optical prism, a mirror surface arranged on one end of the optical prism, and an output surface arranged on another end of the optical prism; a flexible circuit board, the shell being arranged on the flexible circuit board; a light source arranged on the flexible circuit board, the light source being corresponding to the basal plane of the optical prism; and an image sensing unit arranged on the flexible circuit board in correspondence to the output surface of the optical prism.