Optical Fiber Proximity Sensor for Crosstalk Reduction
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Solution Overview
Problem
Portable electronic devices face challenges in reducing the frontal area occupied by proximity sensors while maintaining accurate distance measurement, as existing sensors often suffer from increased crosstalk and reduced accuracy due to the proximity of light sources and detectors to the cover glass.
Innovation Solution
The use of optical multimode fibers, specifically plastic optical fibers with controlled numerical aperture, to direct and receive optical radiation from a light source to an object, minimizing crosstalk and allowing the sensor bulk to be positioned away from the frontal area, with a processor calculating distance based on time-of-flight measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the light source and detector are positioned close to the cover glass for compact design, then the device size is reduced, but optical crosstalk increases and sensing accuracy deteriorates
Solution Approach 1:
Optical fibers serve as intermediary elements between the light source/detector and the cover glass. The fibers transmit optical radiation from the light source to the cover glass and convey reflected radiation from the cover glass to the detector, enabling the light source and detector to be positioned away from the cover glass while maintaining compact device dimensions. This intermediary transmission mechanism reduces optical crosstalk and improves sensing accuracy.
2Use of energy by moving object
If optical fibers with high numerical aperture are used to increase light collection efficiency, then more optical radiation is captured, but optical crosstalk between transmit and receive fibers increases
Solution Approach 1:
The numerical aperture of the optical fibers is precisely controlled and optimized to balance light collection efficiency with crosstalk reduction. By adjusting this critical parameter, the system captures sufficient optical radiation for accurate distance measurement while minimizing unwanted light coupling between adjacent transmit and receive fibers, thereby reducing optical crosstalk.
3Area of stationary object
If the sensor bulk is positioned away from the frontal area using optical fibers, then the frontal area is reduced for sleeker device design, but alignment precision between fibers and cover glass becomes more critical
Solution Approach 1:
The optical fibers act as flexible intermediaries that can be routed from the light source and detector (positioned away from the frontal area) to the cover glass. This intermediary arrangement allows the sensor bulk to be positioned in a less constrained area while maintaining proper optical alignment at the cover glass interface, enabling sleeker device design without sacrificing alignment 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
This configuration reduces optical crosstalk, enhances sensing accuracy, and allows for a more compact design by positioning the sensor components away from the cover glass, improving the opto-mechanical design and reliability of portable electronic devices.
Implementation Method 1
A first optical multimode fiber is configured to receive the emitted beam and to direct the emitted beam toward an object. A second optical multimode fiber is configured to receive the optical radiation reflected from the object and to convey the received optical radiation to the detector.
Implementation Method 2
The range is computed from the time delay between the emission time of the outgoing pulse and the arrival time of the reflected pulse from the object, which is referred to as the 'time of flight' of the optical pulses.
Data Source
AI summary
A proximity sensor includes a light source configured to emit a beam of optical radiation and a detector configured to output an electrical signal in response to the optical radiation that is incident on the detector. A first optical multimode fiber is configured to receive the emitted beam and to direct the emitted beam toward an object. A second optical multimode fiber is configured to receive the optical radiation reflected from the object and to convey the received optical radiation to the detector. A processor is coupled to process the electrical signal so as to compute a distance to the object.