Comparison of the most popular optical fiber senso

2022-09-23
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Comparison of common optical fiber sensors

Fabry Perot (FP), Bragg grating (FBG) and fluorescent optical fiber sensors are currently popular and technologically advanced sensors. Because they are all based on optical fibers, they have many common characteristics, such as anti electromagnetic interference, which can be applied to harsh environments (without adding electromagnetic processes), long transmission distance (slow light attenuation in optical fibers), long service life, compact structure, etc., which will not be repeated here. We will focus on their differences

accuracy

it should be said that they all have high accuracy and can meet the vast majority of needs. But if we carry out in-depth discussion, theoretically, the accuracy that fiber Bragg grating sensor can achieve is high. From the perspective of processing, the sensing accuracy of FP mainly depends on the processing accuracy of cavity length, while the accuracy of FBG mainly depends on the control of grating periodic spacing and effective refractive index. When the machining accuracy is guaranteed, FBG will win by virtue of its excellent linearity in its own measurement mechanism. It can be seen from the sensing principle that FP can be divided into wedge-shaped clamps (referring to taking the change of inclined cavity length into Δλ It is realized through phase change and interference, which is a nonlinear process, and FBG directly through the formula λ B=2neff Λ realize effective refractive index and grating period about Δλ The transformation, completely linear, will theoretically provide better accuracy. In addition, the reflected light of fiber Bragg grating is sharper than FP interference maximum wave packet in the frequency domain, so the measurement of its central spectral line should also be more accurate. The accuracy of fluorescent temperature measurement mainly depends on the characteristics of fluorescent substances excited by fluorescence and the detection of changes in fluorescent light intensity. The current level of technology makes its measurement accuracy equivalent to the first two technologies, and its cost will change with the accuracy and measurement range. However, in actual products, the measurement accuracy is affected by objective factors such as the material, processing level and signal demodulator resolution of the product itself by specific manufacturers, and it is also necessary to make specific comparisons for specific products

integration and group

in this regard, FBG undoubtedly has obvious advantages. The characteristics of fiber Bragg grating make each probe only use a relatively small light source component, and most of the light passes through and continues to propagate. According to the above introduction, up to 30 gratings can be used simultaneously on one fiber, with a transmission distance of more than 45km. This feature undoubtedly brings great convenience to the group. At the same time, the use of wavelength division multiplexing and other technologies also improves the feasibility of this technology. In general, FBG is very suitable for large-scale multi node distributed measurement. As for FP and fluorescent, it will be easier to realize for small-scale networks

complexity

fp and fluorescent system should be much less complex than FBG, among which fluorescent system is the simplest. As explained in the principle part, the first two sensor technologies finally come down to Δλ Obviously, because the signal of FBG is weak and often accompanied by demultiplexing requirements, its system is much more complex than FP. The fluorescent type belongs to light intensity detection, which is relatively simpler

response frequency

response frequency depends more on the design of the network and the response speed of the filtering and demodulation equipment. FBG needs a high-performance demodulation and demultiplexing receiver, and the processing capacity of the receiver often affects its response frequency. The response frequency of FP and fluorescent formula can be generally guaranteed because of their relative simplicity

light source

according to the above discussion, FBG has quite high requirements for light sources, requiring high-power broadband light sources or tunable light sources. The requirements of FP and fluorescent type are much lower, thanks to the strong reflection signal of FP and the fluorescent light source only needs to play the role of excitation fluorescence

flexibility and scope of application

the probes of the three are quite small and flexible, but FBG is obviously subject to its complex wavelength shift detection technology. In the torque environment (300 ° C) where the change angle of the sample is set at a higher temperature, the grating may be erased. Therefore, FBG is not suitable for a large temperature range

cost

according to the above discussion, when it comes to a single measuring point (or a few measuring points, such as less than 50 measuring points), FP and fluorescent systems undoubtedly have advantages because of their low complexity, simple wavelength shift detection technology and low light source requirements. The fluorescent type has the most cost advantage. However, for large-scale systems with more than 50 nodes, the cost of FP and fluorescent will rise rapidly because of the difficulty of their combination

to sum up, it is generally believed that FBG sensors are suitable for large, complex and high-precision low-temperature distributed sensing networks. The advantages of FP and fluorescent type, such as fast response frequency (up to 2120 ° 00khz), small probe size (micron scale), long light source life, are suitable for flexible, small and simple sensing systems. Fluorescent type has the advantages of high temperature measurement and low cost. (end)

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