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How fiber optic sensors work
The basic working principle of the optical fiber sensor is to send the light from the light source into the modulator through the optical fiber, so that the parameter to be measured interacts with the light entering the modulation area, resulting in the optical properties of the light (such as light intensity, wavelength, frequency, phase, Polarization state, etc.) changes, which is called modulated signal light, and then uses the influence of the measured light on the transmission characteristics of the light to complete the measurement.
There are two measurement principles for fiber optic sensors.
(1) Principle of physical optical fiber sensor. Physical optical fiber sensor uses the sensitivity of optical fiber to environmental changes to convert input physical quantities into modulated optical signals. Its working principle is based on the optical modulation effect of optical fiber, that is, the optical fiber's light transmission characteristics, such as phase and light intensity, will change when external environmental factors such as temperature, pressure, electric field, magnetic field, etc. change.
Therefore, if the changes in light phase and light intensity passing through the optical fiber can be measured, the changes in the measured physical quantity can be known. This type of sensor is also called a sensitive element type or functional fiber optic sensor. The point light source beam of the laser is diffused into a parallel wave and divided into two paths through a beam splitter, one is the reference light path and the other is the measurement light path. External parameters (temperature, pressure, vibration, etc.) cause changes in the length of the optical fiber and changes in the phase of the light, thereby producing different numbers of interference fringes. By counting its mode movement, the temperature or pressure can be measured.
(2) Principle of structural optical fiber sensor. Structural optical fiber sensor is a measurement system composed of a light detection element (sensitive element), an optical fiber transmission loop and a measurement circuit. Among them, optical fiber only serves as the propagation medium of light, so it is also called light transmission type or non-functional fiber optic sensor.
