Optical Fingerprint Detection Using Total Internal Reflection
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Solution Overview
Problem
Current optical fingerprint detection methods in LCD displays face challenges with low sensitivity and high interference due to weak diffuse reflection and small signal differences between fingerprint ridges and valleys, requiring high light transmittance and sensor sensitivity.
Innovation Solution
An optical fingerprint detection apparatus featuring a transparent touch panel with a specific angle between its surfaces to achieve total reflection when not touched and non-total reflection when touched by human skin, enhancing contrast and interference resistance by using a light source and detection unit to analyze light intensity distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If diffuse reflection by backlight plate and optical imaging device is used for fingerprint imaging, then identification range can be achieved, but sensitivity and anti-interference capability are significantly reduced due to weak reflected light energy and small signal difference
Solution Approach 1:
The patent inverts the conventional optical path by using a light source on the second surface to illuminate through the touch panel, and using total internal reflection at the first surface to redirect light back through the panel to the detection unit. This inversion creates strong reflected light signals with large intensity differences between ridge and valley areas, resolving the sensitivity and anti-interference capability problems of conventional diffuse reflection methods
Solution Approach 2:
The patent changes the optical parameters by utilizing total internal reflection instead of diffuse reflection, and by adjusting the angle between the first and second surfaces to satisfy the total reflection condition. This parameter change transforms weak reflected light into strong reflected light with enhanced signal contrast, directly improving measurement precision without sacrificing illumination intensity
2Measurement precision
If diffuse reflection method is used, then fingerprint imaging can be achieved, but high requirement for light transmittance and sensor sensitivity is raised
Solution Approach 1:
By inverting the optical path to use total internal reflection at the first surface, the patent generates strong reflected light signals that pass back through the touch panel to the detection unit. This approach reduces the requirements for light transmittance and sensor sensitivity because the reflected light energy is significantly enhanced compared to conventional diffuse reflection methods
Solution Approach 2:
The angled second surface acts as an intermediary element that redirects light from the light source to the first surface at the appropriate angle for total internal reflection. This intermediary structure simplifies the optical system by eliminating the need for complex high-transmittance materials and high-sensitivity sensors required by conventional methods
3Reliability
If conventional optical imaging is used, then fingerprint acquisition can be implemented, but anti-interference capability is low due to small signal difference between ridge and valley
Solution Approach 1:
The patent inverts the conventional optical approach by using total internal reflection to create strong reflected light signals. This inversion produces large intensity differences between ridge areas (where light is reflected back) and valley areas (where light is not reflected), thereby enhancing both anti-interference capability and measurement precision simultaneously
Solution Approach 2:
By changing the optical mechanism from diffuse reflection to total internal reflection and adjusting the surface angle parameters, the patent transforms small signal differences into large signal differences. This parameter change enhances the contrast between ridge and valley signals, improving reliability and anti-interference capability without compromising measurement precision
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
Improves sensitivity and accuracy of fingerprint detection by optimizing light reflection conditions, resulting in clearer contrast between fingerprint ridges and valleys, reducing interference and enhancing detection reliability.
Implementation Method 1
the second surface being configured for receiving the light beam emitted from the light source corresponding to the second surface and angled with respect to the first surface by an angle of less than 90 degrees so as to direct the light beam transmitted through the second surface into the touch panel toward the touch area of the first surface
Implementation Method 2
the touch area being arranged to totally reflect the light beam toward a side of the touch panel opposite to the first surface when the touch area is not touched by the finger or the toe
Implementation Method 3
a detection unit located outside of the side of the touch panel opposite to the first surface and configured for receiving the light beam reflected by the touch area and emitted from the touch panel and detecting an intensity distribution of the received light beam
Data Source
AI summary
An optical fingerprint detection apparatus and a display device are disclosed. The optical fingerprint detection apparatus includes: a light source; a touch panel including a first surface and a second surface, the first surface being provided with at least one touch area, the second surface being configured for receiving the light beam emitted from the light source and angled with respect to the first surface by an angle of less than 90 degrees; and a detection unit located outside of the side of the touch panel opposite to the first surface and configured for receiving the light beam reflected by the touch area and emitted from the touch panel and detecting an intensity distribution of the received light beam.