A high resolution and large range fiber Bragg grating temperature sensor with vortex beams
Introduction
Temperature sensor is a device that can transfer received temperature signals to electrical signals or optical signals and display them, which is widely applied in the industrial field [1]. FBG temperature sensor is an important technical method of temperature measurement. Compared with traditional electronic temperature sensors, it has the advantages of distributed measurement, strong ability for anti-electromagnetic interference, high stability, wide measurement range and small volume [2], [3], [4].
Nowadays, there are kinds of common fiber optic temperature sensor systems [5], [6], including fiber-optic distributed temperature sensor, fiber-optic fluorescence temperature sensor, FBG temperature sensor [7] and so on. Cui Wei and other researchers of Zhejiang University constructed a high-resolution multiplexed FBG wavelength interrogation system, which achieves a temperature resolution of 0.1 °C around 1550 nm [8]. Xie Renwei and other researchers of Tianjin University constructed a FBG temperature sensor and its packaging method for monitoring temperature of aerospace systems, the sensitivity of the temperature sensor is 11.8 pm/°C and the resolution is 0.067 °C as the temperature differs from −70 to 30 °C [9].
Fiber optic sensors based on OAM have unexplored potential. In 2016, in order to realize the digital control of phase shifting in Electronic Speckle Pattern Interferometry (ESPI), Sun Hai proposed a method for out-of-plane displacement measurement by applying phase shifting based on vortex beam [10]. The phase shifting method based on optical vortex does not require mechanical operation, such as optical component movement. Besides, it can improve the stability of phase shift. However, in order to obtain the data of the final displacement, the phase diagram needs to be unwrapped, etc. It is more complicated than our paper, and principle is different from this manuscript. In 2019, Xia Changquan presents a pipeline leakage detection system based on vortex beam [11]. Its principle is that optical fiber deformation causes the displacement, which leads to the change of interference pattern. It provides a feasible and stable method for deformation measurement. However, there is no quantitative analysis of the relationship between deformation and changes in the angle of the interference pattern. It can only judge whether the pipeline leaks by the changes of the interference pattern. This paper not only researches the relationship between the temperature change and the angle rotation of the interference pattern quantitatively, it but also enlarges the temperature measuring range and presents the characteristics of high resolution.
Compared with other fiber sensors, FBG temperature sensor has the advantage of quasi-distributed detection and high-temperature resistance [12]. Its sensing principle is based on the changes of FBG center wavelength with ambient temperature, stress and other factors. The most basic experimental scheme is that obtaining FBG reflection spectral line by adopting broadband source, and thus conducting wavelength modulation through processing spectral line data [13]. However, the wavelength resolution is limited and can not be used for high precision temperature measurement. In order to improve its resolution, this paper proposes a FBG temperature sensing system based on vortex beams, which can realize a high resolution measurement of wide-range temperature changes through the interference properties of the vortex beam and the Gaussian beam.
Section snippets
Principle of fiber Bragg grating temperature measurement
Short-period fiber gratings, also known as FBG or reflection gratings, usually refer to optical gratings with a period close to 1 μm. The characteristic of FBG is the coupling between two core modes with opposite transmission directions. When the light wave passes through FBG, the light wave that meets the Bragg condition will be reflected back to form the Bragg central wavelength, and the shift distance of the central wavelength is an important parameter to realize sensing [14].
When the
Simulation structure
The FBG sensing structure is shown in Fig. 8. The structural parameters of the FBG are as follows: the core RI is 1.4677 at room temperature, the RI of the cladding is 1.4628 and the grating period is 0.5 μm.
Vortex beam is divided into two beams through non-polarizing beam splitter (NPBS). One beam is collimated and coupled into FBG through lens (L1) and microscopic objective (MO1), and after exiting, the beam is expanded and collimated into the Filter through MO2 and L2. The other reference
Results and discussion
Based on wavelength modulation, at different temperatures, the reflection spectrum of vortex beam passing through FBG is monitored to obtain temperature sensitivity. At room temperature, the core RI of FBG is 1.4677 and the diameter is 8 μm; the RI of the cladding is 1.4628 and the diameter is 12 μm; the grating period is 0.5 μm; the wavelength range of the beam source is 1.466 μm–1.495 μm. The wavelength shift on the reflection spectrum is simulated as the temperature changing from 27 °C to
Conclusion
This paper proposes a FBG temperature sensing system based on vortex beams. By the method of detecting the Bragg wavelength shift of the FBG reflection spectrum and the rotation angle of the interference pattern of vortex beam and Gaussian beam at different temperatures, the proposed sensor in this paper owns the characteristic that it can realize high- resolution measurement of a wide range of temperature changes. In the temperature range from 27 °C to 427 °C, the temperature sensitivity of
CRediT authorship contribution statement
Haiwei Fu: Conceptualization, Resources, Writing - review & editing, Funding acquisition. Shuai Wang: Software, Formal analysis, Writing - original draft. Huimin Chang: Validation, Investigation. Yongtao You: Software, Data curation.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work is supported by the National Natural Science Foundation of China (No. 41474108), the Research Foundation of Education Bureau of Shaanxi Province, China (Nos. 12JS077 and 14JS073), the Science and Technology Plan Programin Shaanxi Province of China (Grant Nos. 2019GY-176 and 2019GY-170), and the Innovative and Practical Ability Training Program for Postgraduates of Xi'an Shiyou University (YCS18212057).
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