Tilted fiber Bragg grating design for a simultaneous measurement of temperature and strain

Abstract

Bragg wavelength is sensitive to both temperature and strain changes. Therefore, in sensors that are designed using a fiber Bragg grating (FBG), it is not possible to discriminate the cross-sensitivity of temperature and strain. The design of tilted fiber Bragg gratings (TFBG), which is a family of short-period gratings, has been one of the solutions to this problem. The core mode resonance (LP01) and cladding resonances (LPmn) appear simultaneously in the transmission spectrum. It is possible to perform the simultaneous, independent measurement of temperature and strain using only a TFBG. In this study, the design of a TFBG sensor with a tilt angle of 5° were performed by using the Optigrating 4.2.2 software in order to measure the temperature and strain simultaneously. While the varying temperature was applied to the TFBG in the first stage, the varying strain was applied to it in the second stage, and simultaneously varying temperature and strain were applied to it in the third stage, and linear shifts occurring in wavelengths were calculated using Optigrating. In the design stage of the temperature sensor, research was conducted with different thermal expansion and thermo-optic coefficients, the amounts of shifts caused by these coefficients in the wavelength were examined. It was observed that the change in the wavelength caused by the simultaneous application of temperature and strain was equal to the total change in wavelength that occurred in the non-simultaneous application of temperature and strain.