A IR-Femtosecond Laser Hybrid Sensor to Measure the Thermal Expansion and Thermo-Optical Coefficient of Silica-Based FBG at High Temperatures.

Litong Li,Liangming Xiong,Jie Luo,Dajuan Lv,Minghong Yang

doi:10.3390/s18020359

Litong Li, Liangming Xiong + Show 3 more

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https://doi.org/10.3390/s18020359

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Abstract

In this paper, a hybrid sensor was fabricated using a IR-femtosecond laser to measure the thermal expansion and thermo-optical coefficient of silica-based fiber Bragg gratings (FBGs). The hybrid sensor was composed of an inline fiber Fabry-Perot interferometer (FFPI) cavity and a type-II FBG. Experiment results showed that the type-II FBG had three high reflectivity resonances in the wavelength ranging from 1100 to 1600 nm, showing the peaks in 1.1, 1.3 and 1.5 μm, respectively. The thermal expansion and thermo-optical coefficient (1.3 μm, 1.5 μm) of silica-based FBG, under temperatures ranging from 30 to 1100 °C, had been simultaneously calculated by measuring the wavelength of the type-II FBG and FFPI cavity length.

Highlights

IntroductionFiber Bragg gratings (FBGs) are becoming increasingly important in high temperature application fields such as aerospace engineering, chemical aggressive and energy fields, due to their light weight, immunity to electromagnetic interference, durability against harsh environments, and fast response [1,2]
Fiber Bragg gratings (FBGs) are becoming increasingly important in high temperature application fields such as aerospace engineering, chemical aggressive and energy fields, due to their light weight, immunity to electromagnetic interference, durability against harsh environments, and fast response [1,2].The induced local material changes in silica fiber yield an increase of the refractive index
In previous studies [5,8], theoretical research showed that the wavelength shift of type-II fiber Bragg gratings (FBGs) was mainly determined by the elastic coefficient, thermal expansion coefficient (CTE) and thermo-optical coefficient (TOC)

Summary

Introduction

Fiber Bragg gratings (FBGs) are becoming increasingly important in high temperature application fields such as aerospace engineering, chemical aggressive and energy fields, due to their light weight, immunity to electromagnetic interference, durability against harsh environments, and fast response [1,2]. In 2016, the type-II gratings within silica suspended-core microstructure optical fibers fabricated by femtosecond lasers were tested at temperatures up to 1300 ◦ C [11]. Some of these FBGs still have certain limitations, such as the inscription difficulty of SFBGs, and the frangibility and low reflection intensity of RFBGs after repeated annealing. In previous studies [5,8], theoretical research showed that the wavelength shift of type-II FBGs was mainly determined by the elastic coefficient, thermal expansion coefficient (CTE) and thermo-optical coefficient (TOC).

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Results and Discussion

Conclusions