Elsevier

Optical Fiber Technology

Volume 60, December 2020, 102369
Optical Fiber Technology

A high resolution and large range fiber Bragg grating temperature sensor with vortex beams

https://doi.org/10.1016/j.yofte.2020.102369Get rights and content

Highlights

  • An effective method for the determination of temperature is proposed.

  • A fiber Bragg grating temperature sensor based on vortex light is designed.

  • The sensor achieves temperature measurement of high resolution and wide range.

  • The resolution can be adjusted by the length of the grating.

Abstract

The vortex beam owns helical phase factor, orbital angular momentum, and hollow structure of intensity distribution. It is widely applied in information coding, optical manipulation and optical sensing. This paper attempts to design a fiber Bragg temperature sensor based on vortex light, including an orbital angular momentum (OAM) beam transmitted by fiber Bragg grating (FBG), an optical fiber path used to eliminate errors, and a Gaussian beam, which is used to interfere with FBG transmission light. The interference pattern of a Gaussian beam and an OAM beam rotates with the changes of phase difference between the two beams. When the temperature changes, FBG is affected by the thermal optical effect and thermal expansion effect, and the central wavelength of the reflected spectrum will shift. Based on the relationship between wavelength shift and temperature change, temperature measurement in a large range can be realized. Additionally, the Filter is placed behind the FBG, and the transmission light (λ=1.466μm) with less reflection is selected to interfere with the Gaussian light, with the change of phase of transmission light, the rotation of the interference pattern will change accordingly. The temperature change corresponding to the 2π rotation of the interference pattern can be obtained, thus temperature measurement with high resolution can be realized. The simulation results show that when the temperature range is 27 °C–427 °C, the sensitivity of this sensor is 14.42 pm/°C. On the basis of the rotation of the interference pattern, when the rotation angle of the temperature-induced interference pattern change within 2π the temperature sensitivity is 1.529 rad/°C, based on the angular resolution of CCD, the theoretical resolution of temperature measurement is 6.3e−7 °C. Similar to the cursor effect, the main ruler measures a wide range of temperature changes according to wavelength drift, and the cursor is a high-resolution measurement of temperature according to the rotation angle of the interference pattern.

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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