Fiber optic sensorAccording to their working principles, they can be divided into two categories: functional (also known as physical type or sensing type) and non functional (also known as structural type or light transmission type). Functional fiber optic sensors not only use optical fibers as waveguides for light propagation, but also have measurement functions. It can use external physical factors to change the intensity, phase, polarization state, or wavelength of light in optical fibers, thereby measuring and transmitting data on external factors. Non functional fiber optic sensors only use optical fibers as a medium for transmitting light, and other sensitive components need to be added to form the sensor.

1Functional fiber optic sensor

Functional fiber optic sensors can be divided into amplitude modulation type, phase modulation type, and polarization modulation type. A sensor that detects changes in light intensity using optical fibers under the influence of external physical quantities is called an amplitude modulation sensor. The specific methods of using multimode optical fibers to construct amplitude modulation sensors include: changing the absorption characteristics of optical fibers towards light waves; Changing the refractive index distribution in optical fibers to alter the transmission power; Change the micro bending state in optical fibers, etc. Detecting various physical quantities by utilizing the influence of external factors on the phase of light waves in optical fiberssensorIt is called a phase modulation sensor. The sensor that detects changes in the transverse polarization state of optical fibers caused by external factors is called a polarization modulation sensor.

2、 Non functional fiber optic sensor

Non functional fiber optic sensorThe structure is relatively simple and can fully utilize the characteristics of optoelectronic components and optical fibers, so it is highly valued.

1. Fiber optic displacement sensor

Fiber optic displacement sensorIt utilizes the function of optical fiber to transmit optical signals and measures the distance between the measured object and the reflecting surface based on the intensity of the detected reflected light. Its working principle is that when the end of the fiber optic probe is tightly attached to the measured object, the light in the transmitting fiber cannot be reflected into the receiving fiber, so no electrical signal can be generated in the optoelectronic component; As the measured surface gradually moves away from the fiber optic probe, the area illuminated by the emitting fiber on the measured surface becomes larger, and the corresponding overlapping area of the emitting and receiving cones becomes larger. Therefore, the illuminated area on the receiving fiber end face also becomes larger, resulting in a linearly increasing output signal; When the entire receiving fiber end face is illuminated, the output signal reaches the "peak point" on the displacement output signal curve; the curve range is narrow, but the sensitivity is high and the linearity is good, suitable for measuring small displacements and surface roughness. The signal attenuation is inversely proportional to the square of the distance between the probe and the measured surface.

Standard fiber optic displacementsensorA fiber optic cable with a diameter of 0.762 mm is composed of 600 optical cores. There are four types of combinations for transmitting and receiving optical fibers: hybrid, hemispherical half split, coaxial internal transmission distribution, and coaxial external transmission distribution. The sensitivity of the mixed type is the highest, while the I range of the half fraction is the largest.

2.Fiber optic temperature sensor

In addition to the phase modulation method introduced above, there are many other methods for fiber optic temperature measurement technology. One of them is to utilize the characteristic of the measured surface radiation energy changing with temperature, and use optical fibers to transmit the radiation energy to the thermistor, which is then converted into an electrical signal that can be recorded and displayed. At present, the measurement of explosion temperature of liquid explosives adopts colorimetric temperature measurement method, which uses optical fibers to transmit explosion radiation energy. The unique feature of this method is that it allows for remote measurement.

3. Optical frequency modulation typeFiber optic sensor

Optical frequency modulation is based on the Doppler effect of the human incident light frequency and its reflected light of the object being measured, so it is mainly used to measure the velocity of moving objects. If the frequency of light shines on a moving object with relative velocity, the frequency of the light reflected from the moving object changes.