Fiber Bragg Grating Sensor Based on Refractive Index Segment Code of Mobile Modulation
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Fiber Bragg Grating Sensor Based on Refractive Index Segment Code of Mobile Modulation Juan Wang 1,2 & Zhi-chao Liu 1 & Jin-hua Yang 1 Accepted: 23 September 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Fiber Bragg Grating (FBG) is achieved by refractive index modulation. Temperature and strain can be measured by FBG. The echo spectral distribution is determined by the refractive index of the fiber and the grating pitch. Therefore, there are few types of conventional refractive index modulation methods, and there are few types of echo spectrum. In this paper, an index code modulation based on IoT method was proposed. The FBG is divided into a plurality of interval segments in the method. The spectral shape of the echo is controlled by encoding and modulating each interval. When the segment size satisfies some requirements, the positive and negative modes of the sub-FBG are calculated by the coupled-mode theory, and then the mode functions of each segment are solved by the matrix transmission algorithm. The equivalent function of the reflectance distribution field is obtained. According to the relevant parameters of FBG, the mathematical model of the FBG modulation spectral distribution is established by the refractive index modulation method. Through the simulation analysis of the fractional refractive index modulation, the results show that the echo spectral peak, half-width, etc. have a larger tunable range. In the experiment, a femtosecond laser was used to accurately encode and modulate the refractive index, and two different types of segmented FBGs were fabricated according to design requirements. The experimental results show that the design of different segmented structures has a significant impact on the spectral distribution of the echo. Spectral shape control can be achieved by refractive index modulation method. Keywords Fiber Bragg Grating (FBG) . Fractional modulation . Refractive index encoding . Matrix transmission algorithm
1 Introduction FBG sensing system by the transmission fiber will be a large number of FBG sensors connected to form a distributed test network. It can monitor temperature and strain simultaneously at multiple locations [1]. In recent years, FBG sensing systems are widely used in structural health monitoring [2, 3], aerospace monitoring [4–6], coalmine monitoring [7], oil industry monitoring Industry Monitoring [8–10], a wide range of granary food temperature monitoring [11] and so on. It has the advantages of high sensitivity, good stability and no electromagnetic * Jin-hua Yang [email protected] 1
School of Opto-Electronic Engineering, Changchun University of Science and Technology, Changchun 130022, China
2
Jilin Vocational College of Industry and Technology, Jilin 132000, China
interference. However, there are still some problems, such as the cross-sensitivity of temperature and strain, the small amount of information of echo spectrum data and so on. In order to solve these problems, researchers have been working hard to develop vari
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