Optical Fingerprint Sensor Light Guiding Layer Illumination
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Solution Overview
Problem
Existing optical fingerprint sensors face challenges in achieving uniform illumination of the sensing area, leading to suboptimal image quality and recognition accuracy due to light loss and stray light issues, particularly when embedded under a thick glass cover.
Innovation Solution
The optical fingerprint sensor incorporates a light guiding layer with multiple refractive index materials and structures, such as apertures, prisms, and material blocks, to reduce light losses and ensure uniform illumination, while preventing stray light from reaching the image sensor array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a light source illuminates the sensing area, then the sensing area receives light, but the illumination is not uniform
Solution Approach 1:
The patent introduces a light guiding layer as an intermediary component between the light source and the sensing area. This layer guides and distributes light uniformly across the sensing area while minimizing light loss through its optical properties and structural design.
Solution Approach 2:
The patent modifies optical parameters by using materials with different refractive indices in the light guiding layer to control light propagation, reflection, and distribution, achieving uniform illumination while reducing light loss.
2Strength
If the optical fingerprint sensor is embedded under a thick glass cover, then the device structure is protected, but light transmission is reduced
Solution Approach 1:
The light guiding layer acts as an intermediary that compensates for the light transmission loss caused by the thick glass cover, maintaining sufficient light intensity for fingerprint sensing while preserving the protective function of the glass cover.
Solution Approach 2:
The patent optimizes optical parameters by selecting materials with appropriate refractive indices for the light guiding layer, which compensates for light attenuation through the thick glass cover and maintains effective light transmission.
3Measurement precision
If the light source illuminates the sensing area, then fingerprint imaging is enabled, but stray light reaches the image sensor array
Solution Approach 1:
The light guiding layer serves as an intermediary that directs light precisely to the sensing area while blocking stray light from reaching the image sensor array, improving imaging quality by eliminating harmful stray light interference.
Solution Approach 2:
The patent applies local quality control by designing the light guiding layer to provide directional light distribution, ensuring that light reaches only the intended sensing area while preventing stray light from reaching other regions including the image sensor array.
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 configuration enhances light transmission efficiency, achieves uniform illumination of the sensing area, and improves fingerprint recognition accuracy by filtering out non-reflective stray light, thereby improving image quality and recognition performance.
Implementation Method 1
The light guiding layer is disposed on the collimator layer. The light guiding layer allows a portion of the light from the light source to enter to the sensing area while directing the remaining portion of the light forward
Implementation Method 2
each of the prisms reflects a portion of incident light to the sensing area and passes the remaining portion of the incident light
Data Source
AI summary
An optical fingerprint sensor, includes: an image sensor array; a collimator layer disposed above the image sensor array, the collimator array having an array of first apertures; a light guiding layer disposed on the collimator layer; a light source emitting light into the light guiding layer; and a sensing area disposed above the light guiding layer. The light guiding layer allows a portion of the light from the light source to enter to the sensing area while directing the remaining portion of the light forward.