Characterization of fibre Bragg gratings for temperature and strain sensing

Abstract

Since their introduction in the mid seventies, a variety of fibre optic sensor configurations have been developed for the measurement of strain, deformation, temperature, vibration, pressure, etc. Variation of these parameters alters the refractive index and the geometric properties of the optical fibre, which in turn perturbs the intensity, phase, or polarization of the light wave propagating in the waveguide. Only in the past decade that Bragg grating-based fibre optic sensors emerged as the non-disputed champion in multiplexing and dual parameter sensing with increased potential for smart structure applications. Stringent requirements for single point discrete or distributed simultaneous strain and temperature measurements prompted this characterization study which has the objective of developing a detailed understanding of grating characteristics and response under external stimuli. Collocated and serially placed gratings were evaluated and tested for their effective sensitivity to strain and temperature and to coating materials variation such as polyamide and acrylite. Experimental sensitivity results correlated well with theoretical estimation for strain in single gratings. Whereas, significant wavelength differential is required for simultaneous temperature and strain measurement if collocated gratings are used.

Bent tilted fiber Bragg gratings for temperature-independent vibration sensing in vehicles

“…As expected from Equation 3 the whole spectrum shifted in wavelength as the grating was cooled from 70°C down to -6°C, however the depth of the Bragg and the Ghost mode remained the same, which is shown in Figure 6 where all of the traces were overlapped with the -6°C trace. The temperature sensitivity of the Bragg was determined to be 9.8pm/°C which is consistent with the results previously reported for that type of fiber [9]. To demonstrate the multiplexing capability the fiber containing TFBG was immersed in refractive index matching liquids.…”