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Structural principle and classification of fiber optic sensors

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1, fiber optic sensor structure principle
A conventional electric-based sensor is a device that converts the measured state into a measurable electrical signal. Its power supplies, sensitive components, signal receiving and processing systems, and information transmission are all connected by metal wires. A fiber optic sensor is a device that converts the measured state into a measurable optical signal. It consists of an optical transmitter, a sensitive component (optical or non-optical), an optical receiver, a signal processing system, and an optical fiber.
Light emitted by the optical transmitter is directed through the source fiber to the sensitive component. At this time, a certain property of the light is modulated by the measurement, the dimmed light is coupled to the optical receiver via the receiving fiber, the optical signal is converted into an electrical signal, and finally the signal is processed to obtain the desired measurement.
 
It can be seen that fiber optic sensors have fundamental differences in measurement principles compared to conventional electric-based sensors. Traditional sensors are based on machine-to-electric measurements, while fiber optic sensors are based on optical measurements.
  Light is an electromagnetic wave with a wavelength ranging from a very far infrared of 1 mm to a very distant ultraviolet 10 nm. Its physical and biochemical effects are mainly caused by the electric field. Therefore, the discussion of sensitive measurements of light must take into account the vibration of the electrical vector E of the light, ie
 
A——the amplitude vector of the electric field E; ω——the vibration frequency of the light wave;
Φ——optical phase; t——the propagation time of light.
It can be seen that as long as one of the parameters of the intensity, the polarization state (the direction of the vector A), the frequency and the phase of the light changes with the measured state, or is modulated by the measurement, the intensity modulation and the polarization modulation of the light are adopted. Demodulation by frequency modulation or phase modulation, etc., to obtain the required measured information.
 
2, the classification of fiber optic sensors
 
Note: MM multimode; SM single mode; PM polarization retention; a, b, c functional, non-functional, light pick-up