VCSEL Fire Sensor Self-Mixing Interference for False Alarm Reduction
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Solution Overview
Problem
Existing optical fire detectors face challenges in accurately distinguishing between fires and false alarms, particularly in complex smoke patterns, and require additional sensors to mitigate false positives, while also being bulky and aesthetically unappealing.
Innovation Solution
An optical fire sensor device utilizing a VCSEL laser diode with integrated photodiode and self-mixing interference method to detect particle size and speed within a small measurement volume, enabling precise identification of smoke patterns and potentially omitting the need for an optical chamber, with a fire detection unit that compares measured values to predetermined criteria and outputs an alarm signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional sensors (LED sensors, temperature sensors, CO sensors) are used to differentiate fires from false alarms, then reliability of fire detection is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple detection functions into a single optical sensor system. The VCSEL laser diode with integrated photodiode performs both particle detection and speed measurement through self-mixing interference, eliminating the need for separate LED sensors, temperature sensors, and CO sensors while maintaining reliable fire detection capability.
Solution Approach 2:
The optical sensor device is designed to perform multiple functions using a single sensor system. It can detect particle presence, determine particle speed, and differentiate fire smoke from false alarm sources (dust, steam, cigarette smoke) all through the same VCSEL-photodiode assembly, making the sensor universal for various detection needs.
2Measurement precision
If incoherent light with long optical path (several centimeters) is used to achieve sufficient signal strength, then measurement precision is improved, but device size increases
Solution Approach 1:
The patent changes the fundamental parameters of the light source from incoherent to coherent (laser), and modifies the optical path configuration. The VCSEL laser provides high coherence and intensity, allowing effective measurement in a compact volume without requiring several centimeters of optical path length, thus achieving strong signal strength in a small device footprint.
Solution Approach 2:
The self-mixing interference technique utilizes periodic modulation of the laser intensity caused by backscattered light from particles. This periodic action enhances the detection sensitivity and signal strength, allowing precise measurements to be obtained in a compact device without requiring long optical paths.
3Volume of moving object
If VCSEL laser diode with self-mixing interference method is used to detect particles in small volume, then device size is reduced, but difficulty of detecting and measuring increases
Solution Approach 1:
The self-mixing interference method implements an optical feedback mechanism where light backscattered from particles is fed back into the VCSEL laser cavity. This feedback modulates the laser intensity in a way that encodes particle information, simplifying the detection process despite the small measurement volume and enabling particle detection through intensity modulation analysis.
Solution Approach 2:
The VCSEL laser diode serves multiple functions simultaneously: it acts as the light source, the interferometer, and the detector through the self-mixing effect. The laser automatically performs the measurement function without requiring separate external components, making the system self-sufficient and simplifying the overall detection architecture despite operating in a compact volume.
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
Enables precise detection of fires and their types with reduced device size, improved handling, and external analysis of complex smoke patterns, enhancing accuracy and aesthetic appeal by using focused high-intensity, coherent measurement beams.
Implementation Method 1
An optical fire sensor device is proposed, which uses a focused, high-intensity, coherent measurement beam for particle detection
Implementation Method 2
They operate according to the scattered light method, which is based on the fact that smoke particles in an optical chamber of the fire detector scatter a test light beam
Implementation Method 3
an optical detector unit (50b), in particular a photodiode, integrated into the VCSEL sensor chip (66)
Implementation Method 4
By means of the self-mixing interference technique, the known optical particle sensor device enables items of information to be obtained with respect to a presence of particles, in particular particle number and particle speed
Implementation Method 5
The self-mixing interference method is described, for example, in G. Giuliani et al., Laser Diode Self-Mixing Technique for Sensing Applications, Journal of Optics A: Pure and Applied Optics, 2002, 4, page 283-page 294. It is based on a measurement beam backscattered by a particle interfering with the emitted measurement beam and thus modulating the emitted intensity of the measurement beam
Data Source
AI summary
The present invention provides an optical fire sensor device and a corresponding fire detection method. The optical fire sensor device is equipped with an optical particle detection unit (10), which is configured to ascertain measured values of a particle number in a measurement volume range (FA) as a function of a particle size in a predetermined particle size range and/or as a function of a particle speed in a predetermined particle speed range, a fire detection unit (20), which is configured to ascertain respective distributions of the measured values and to compare at least one parameter of the ascertained distributions to at least one predetermined criterion. The fire detection unit (20) is configured to detect a fire (B) in consideration of the comparison. An alarm unit (30, 40) is used to output an alarm signal in response to the detection of the fire (B) by the fire detection unit (20).