Off-Axis Angular Light Capture for Under-Display Fingerprint Sensing
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Solution Overview
Problem
Under-display fingerprint sensing systems face challenges with low contrast and low signal-to-noise ratio due to low-light throughput and diffraction caused by the display stack, leading to poor quality fingerprint images.
Innovation Solution
The implementation of off-axis angular light capture using an optical coupling layer with Fresnel prisms and a collimator layer, which directs and collimates reflected light at an angle of about 42°, combined with polarizer layers to enhance contrast and reduce noise, effectively improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional display stack structure is used for under-display fingerprint sensing, then device integration is achieved, but light throughput is reduced and diffraction occurs causing low contrast and poor image quality
Solution Approach 1:
The patent introduces an optical coupling layer with Fresnel prisms as an intermediary component between the display stack and the fingerprint sensor. This intermediary structure redirects diffracted light at specific angles (including 42°) to the sensor, acting as a mediator that recovers light paths that would otherwise be lost, thereby improving image quality while maintaining device integration
Solution Approach 2:
The patent changes the optical parameters by introducing angle-selective filtering using polarizer layers and Fresnel prism structures. These components modify the angular distribution of light reaching the sensor, enhancing specific off-axis angles (such as 42°) while suppressing others, thereby improving contrast and signal-to-noise ratio without compromising integration
2Device complexity
If conventional normal-light imaging is used, then system simplicity is maintained, but imaging signal strength is insufficient leading to low contrast
Solution Approach 1:
The patent transitions from conventional normal-light (0° incidence) imaging to off-axis angular light imaging. By utilizing light at specific angles (such as 42° off-axis) instead of only normal incidence light, the system captures stronger imaging signals from the fingerprint surface, enhancing contrast while adding angular dimensionality to the imaging process
Solution Approach 2:
The patent changes the illumination and detection angular parameters by introducing Fresnel prisms and polarizer layers that select and enhance off-axis light paths. This parameter modification enables the system to capture stronger signals from oblique light while maintaining relatively simple system architecture through the use of planar optical components
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 solution enhances fingerprint image contrast and maintains the compactness of the sensing system by capturing stronger imaging signals from oblique light, resulting in improved ridge-valley contrast and signal-to-noise ratio.
Implementation Method 1
The optical coupling layer may be an optical layer made of a planar array of Fresnel prisms
Implementation Method 2
The optical coupling layer bends the reflected light rays to create oblique light rays
Implementation Method 3
The collimator layer includes a number of apertures to collimate the received light rays
Implementation Method 4
combined with polarizer layers to enhance contrast and reduce noise
Data Source
AI summary
An apparatus for touch-sensing includes a light-emitting layer covered by a transparent layer and configured to illuminate a surface touching the transparent layer and to allow transmission of reflected light rays from the surface to underlying layers. The underlying layers include an optical coupling layer, a collimator layer and a pixelated image sensor. The optical coupling layer bends the reflected light rays to create oblique light rays. The collimator layer includes a number of apertures to collimate the received light rays. The pixelated image sensor senses the collimated oblique light rays.