Flat Panel Optical Sensor Using Holographic Light Expansion
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Solution Overview
Problem
Conventional optical and capacitive fingerprint sensors face limitations in recognizing fingerprint patterns due to diffused light and complex assembly structures, respectively, which restrict their application in portable devices, and the use of protective films further degrades their performance.
Innovation Solution
A flat panel display embedding an ultra-thin optical image sensor with a directional light source and a low refractive layer, where collimated light is expanded using holographic films to cover a large area without losing intensity, allowing for high-resolution and sensitive fingerprint recognition within a thin form factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If diffused light is used for optical fingerprint sensing, then the light source can cover a wide area, but the fingerprint pattern recognition precision deteriorates
Solution Approach 1:
A light guiding layer is introduced as an intermediary between the light source and the fingerprint sensing area. This layer guides and directs the light from the LED source to illuminate the fingerprint pattern with improved directionality, enabling both wide area coverage and sufficient resolution for accurate fingerprint recognition.
2Measurement precision
If collimated light is used for optical fingerprint sensing, then the fingerprint pattern recognition precision improves, but the sensing area is restricted to a small area
Solution Approach 1:
The light guiding layer extends the light propagation in a controlled manner through the thickness dimension of the sensor structure, allowing collimated light to cover a larger planar area while maintaining its directional properties and illumination intensity across the extended sensing region.
3Area of stationary object
If a scanning structure is used to radiate collimated light over a wider area, then the sensing area increases, but the device complexity increases making it unsuitable for portable devices
Solution Approach 1:
The complex scanning mechanism is extracted and replaced by a static light guiding layer that passively distributes light across the sensing area. This eliminates moving parts and complex control systems while maintaining wide area coverage with collimated light.
4Strength
If a protective film is added to protect the display, then the display durability improves, but the fingerprint sensor performance deteriorates
Solution Approach 1:
The optical fingerprint sensing system replaces the mechanical contact-based capacitive sensing with optical detection that can function through the protective film. The light-based sensing mechanism is insensitive to the physical presence of the protective film, maintaining both display protection and sensor performance.
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 provides high-resolution and sensitive fingerprint recognition over a large area without increasing the device thickness, enabling its application in various portable devices while maintaining the display area for image display.
Implementation Method 1
a light guiding layer disposed between the light source and the fingerprint pattern
Implementation Method 2
a low refractive index layer disposed between the cover plate and the light guiding layer
Implementation Method 3
reduces the total internal reflection of light incident on an interface between the cover plate and air
Data Source
AI summary
The present disclosure relates to a flat panel display embedding an optical imaging sensor such as a fingerprint image sensor. The present disclosure suggests a flat panel type optical image sensor comprising: a cover plate having a sensing area; a light incident film disposed at a side under the cover plate; a light radiating film disposed under the cover plate corresponding to the sensing area; a low refractive layer under the light incident film and the light radiating film; a light source disposed under the light incident film; and a light sensor disposed under the light incident film.