Principles of Fiber Optic Sensors

The basic working principle of optical fiber sensor is to light through the optical fiber from the light source to the modulator, the parameters and enter the modulation OuDeGuang interaction under test, leading to the optical properties of the light (such as light intensity, wavelength, frequency, phase, polarization, etc.) change, called a modulated signal light, recycled by measuring the transmission properties of optical influence, to complete the measurement.

1.Structure of optical fiber

2. Light transmission principle of optical fiber

3. Working principle of optical fiber sensor

(1) functional type — made by using certain sensitive characteristics or functions of the fiber itself

(2) optical transmission type — the optical fiber only plays the role of transmitting light. It adds other sensitive elements in the end or middle of the optical fiber to feel the measured changes.

There are two kinds of measurement principles of optical fiber sensor.

(1) principle of physical fiber sensor. Physical fiber sensor USES the sensitivity of optical fiber to environmental changes to transform physical input into modulated optical signal.Its working principle is based on the optical modulation effect of optical fiber, that is, when the external environmental factors such as temperature, pressure, electric field, magnetic field and so on change, its light transmission characteristics, such as phase and light intensity, will change.

Therefore, if the changes of phase and intensity of light passing through the optical fiber can be measured, the changes of the measured physical quantity can be known.This kind of sensor is also called sensor type or functional optical fiber sensor.The laser’s point light beam diffuses into parallel waves and is divided into two paths by the splitter, one is the reference path and the other is the measurement path.External parameters (temperature, pressure, vibration, etc.) cause changes in the length of the optical fiber and phase of the light phase changes, so as to produce a different number of interference fringes, the mode of its movement to count, you can measure the temperature or pressure.

(2) principle of structural fiber sensor. Structural fiber sensor is a measurement system composed of optical detection element (sensitive element), optical transmission circuit and measurement circuit.Among them, optical fiber only serves as the medium of light transmission, so it is also called light-transmitting or non-functional optical fiber sensor.

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