Four common optical fiber sensors and their selection basis

Optical fiber sensor is a kind of sensor that converts the state of the measured object into measurable optical signal. It can adapt to all kinds of bad weather conditions and can transmit long distance without additional power supply. With the continuous development of sensors in the direction of accuracy, sensitivity and compactness, optical fiber sensors are becoming more and more popular as new members. In order to improve your understanding of optical fiber sensors, the following are the four common optical fiber sensors and their selection basis, which I hope can provide you with reference and help.

(1) Fiber optic gyroscope

Fiber optic gyroscope can be divided into interference type, resonance type and Brillouin type according to principle, and is the representative of three generations of fiber optic gyroscope. At the beginning of the 21st century, the first generation of interferometric fiber optic gyroscope technology is mature and suitable for mass production and commercialization. The second generation resonant fiber optic gyroscope is still in the stage of laboratory research and practical development. The third generation Brillouin type is still in the stage of theoretical research.

According to the optical elements used, there are three ways to realize the FOG structure: small discrete element system, all-fiber system and integrated optical element system. At the beginning of the 21st century, the technology of separating optical elements was basically withdrawn. The all-fiber system is used for open-loop fiber optic gyroscope with low accuracy and low cost. Due to its simple process, good overall repeatability and low cost, integrated optical device gyroscope is very popular in high-precision fiber optic gyroscope and is its main implementation method.

(2) Fiber grating sensor

Fiber Bragg grating sensor is one of the research hotspots in the field of optical fiber sensors at home and abroad. Traditional optical fiber sensors can be basically divided into two types: light intensity type and interference type. The disadvantages of light intensity sensor are unstable light source, fiber loss and easy aging of detector. The interference sensor requires the same light intensity of two kinds of interference light, so it needs to fix the reference point, which makes the application inconvenient. The fiber grating sensor based on fiber Bragg grating developed at the beginning of the 21st century can avoid the above two situations. Its sensing signal is wavelength modulated and has strong multiplexing capability. Fiber grating sensor is the most ideal sensitive element in building health detection, impact detection, shape control and vibration damping detection. Fiber grating sensors are widely used in geodynamics, spacecraft, power industry and chemical sensors.

(3) Optical fiber current sensor

With the rapid development of the power industry, the capacity of the power transmission system continues to increase, the operating voltage level is getting higher and higher, and the current is getting larger and larger, which is difficult to measure. This shows the advantages of the optical fiber current sensor. In the power system, the traditional sensor used to measure current is based on electromagnetic induction, which has the following disadvantages: explosive and even catastrophic accidents; Large fault current will cause magnetic saturation of iron core; Core resonance effect; Slow frequency response; Low measurement accuracy; The signal is vulnerable to interference; It is difficult to meet the development needs of the new generation of digital power grid due to its large volume, weight and high price. At this time, optical fiber current sensor came into being and was widely used.

(4) Fiber optic hydrophone

Optical fiber hydrophone is mainly used to measure underwater acoustic signals. It converts underwater acoustic signals into optical signals through high-sensitivity optical fiber coherent detection, and transmits them to signal processing system through optical fiber for identification. Compared with the traditional hydrophone, the fiber-optic hydrophone has the characteristics of high sensitivity, wide response band and no electromagnetic interference. Widely used in military, oil exploration, environmental detection and other fields, it has great development potential.

Fiber optic hydrophones can be divided into interference type, intensity type and grating type according to the principle. The key technology of interferometric fiber-optic hydrophone has gradually developed and matured, and products have been formed in some fields. Fiber grating hydrophone is a hot research topic at present. Key technologies include light source, optical fiber equipment, probe technology, anti-polarization fading technology, anti-phase fading technology, signal processing technology, multiplexing technology and engineering technology.

As for the selection of optical fiber sensor, the type is mainly determined according to the measurement object and environment. Carefully analyze the measurement work and consider which principle of sensor to use for measurement, because even if the same physical quantity is measured, it can be achieved by different principles. Secondly, the measurement range, volume (whether the space is enough), installation method, signal type (analog or digital signal), measurement method (direct or indirect measurement), etc. must be considered.

Accuracy of optical fiber sensor

The accuracy grade of the sensor relates to the accuracy of the whole system and is a very important parameter. Generally speaking, the higher the accuracy, the more expensive the price. Therefore, when selecting, we should consider the best from the overall perspective. Don't blindly pursue the so-called high accuracy. Unless we need to measure the accuracy value quantitatively, we should select the sensor with higher accuracy level.

Selection of sensitivity

Sensitivity refers to the ratio of output increment to corresponding input increment. We must correctly understand this parameter in two aspects: 1. In the online range, it has high sensitivity and large output signal value, which is an advantage. 2. High sensitivity, external noise irrelevant to measurement is easy to mix, which affects the accuracy of processing.

Linear range

Linear range refers to the range in which the output is proportional to the input, so we all hope that the wider the linear range is, the better the precision is. However, the linear range of any sensor is relative. In order to be within the linear range, we only need to estimate the measurement.

Frequency response characteristics

During the measurement process, the output of the sensor always has a certain delay, which is different from the actual value. Therefore, we hope that the frequency response will be faster, so the delay time will be shorter. However, due to the influence of structure and other characteristics, it is difficult to improve the frequency.

stability

Stability means that its performance can remain unchanged after long-term use. In addition to its own reasons, the main factors affecting stability are environmental factors. Therefore, the selected sensor should have strong environmental adaptability and take protective measures when appropriate.