Fingerprint Sensor Optical Element for Thin Stray-Light Suppression
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Solution Overview
Problem
Existing fingerprint recognition sensors face challenges in achieving a high signal-to-noise ratio (S/N ratio) while being able to thin the sensor, particularly due to issues with stray light interference.
Innovation Solution
Incorporating a near infrared absorbing dichroic substance in the optical element with specific absorption axes orientations, either in multiple layers or a single layer with aligned dichroic substances, to selectively absorb stray light and enhance the S/N ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an optical member including a louver film is used, then the S/N ratio of desired light increases, but the fingerprint recognition sensor cannot be thinned
Solution Approach 1:
The patent changes the optical parameters of the optical member by incorporating a near-infrared absorbing dichroic substance with specific absorption characteristics. This substance has an absorption axis that creates different absorbance values for light incident from different directions (greater absorbance from oblique directions than from normal direction), thereby improving S/N ratio without requiring increased thickness
Solution Approach 2:
The patent uses a composite optical member that combines a near-infrared absorbing dichroic substance with other materials. This composite structure achieves both stray light suppression and maintains thin profile by leveraging the unique optical properties of the dichroic substance rather than relying on thick louver film structures
2Device complexity
If the optical element uses a single layer with aligned dichroic substances, then the device complexity is reduced, but the S/N ratio improvement may be insufficient
Solution Approach 1:
The patent applies local quality by orienting the absorption axes of dichroic substances in specific directions within the optical member. By controlling the local orientation of absorption axes (e.g., radial or tangential alignment in a disk-like structure), the optical element achieves effective stray light suppression while maintaining structural simplicity
Solution Approach 2:
The patent exploits asymmetry in the absorption characteristics of the dichroic substance, where absorbance varies with the angle of light incidence. This asymmetric absorption property allows the optical member to differentiate between light from different directions, improving S/N ratio through the inherent optical anisotropy rather than complex multi-layer structures
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 results in a fingerprint recognition sensor with an improved S/N ratio and the ability to be thinner, effectively mitigating stray light interference and enhancing recognition accuracy.
Implementation Method 1
an optical element that includes a near infrared absorbing dichroic substance
Implementation Method 2
the optical element has an absorption axis with respect to near infrared light in an in-plane direction, and in a case where linearly polarized light of near infrared light orthogonal to the absorption axis is radiated from a normal direction of the optical element and from a direction inclined by 45° from the normal direction at an azimuthal angle orthogonal to the absorption axis, an absorbance during the radiation from the direction inclined by 45° from the normal direction is more than an absorbance during the radiation from the normal direction
Data Source
AI summary
A sensor including a light-receiving element; and an optical element that includes near infrared absorbing dichroic substance. The optical element has an absorption axis with respect to near infrared light in an in-plane direction. When linearly polarized light of near infrared light orthogonal to the absorption axis is radiated from a normal direction of the optical element and from a direction inclined by 45° from the normal direction at an azimuthal angle orthogonal to the absorption axis, an absorbance during the radiation from the direction inclined by 45° from the normal direction is more than an absorbance during the radiation from the normal direction.