This paper presents an analysis of birefringence and regeneration of fibre Bragg gratings (FBGs) in two types of polarization-maintaining (PM) optical fibres, bow tie and internal elliptical cladding (IEC), with different diameters. The thermal regeneration of FBGs in PM fibres with different degrees of saturation (weakly, slightly, and strongly saturated) is presented and the influence of the gratings’ saturation degree on the birefringence of PM fibres is shown. The birefringence values obtained for IEC fibres with 80 µm of diameter were for a strongly saturated seed grating of 5.3 × 10−4 and 6.2 × 10−4 refractive index units after the regeneration. The evolution of the fibre birefringence as a function of the temperature is presented and the results show hysteresis and nonlinear dependence of the birefringence on temperature. The thermal stability of regenerated gratings in PM fibres is demonstrated, and a sensitivity coefficient value of 0.0035 dBm min−1 at 900 °C was obtained. The results obtained show the feasibility of optimization of fibre birefringence; this could allow such fibers to be used as temperature sensors and even improve the birefringence after the grating regeneration.
We report the fabrication of an hybrid fibre optic and T-shaped microstructrure inscribed in soda lime microscope slides by using femtosecond laser irradiation technique. that allow to construct true 3-D structures. Within the T-shaped structure a FBG was inserted and glued with photopolymer adhesive. The hybrid structure is sensitive to hydrostatic pressure. Calibration load tests were performed in the range 0 − 100 N.
This case study describes a new method using a fiber optic Bragg grating sensor to determine muscle fatigue in a patient wearing a resilient occlusal device for the treatment of bruxism symptoms. Four tasks performed at maximum bite force induced rapid exhaustion for the analysis of fatigue. The results show that it is possible to obtain a better understanding of the muscle fatigue process by using the fiber sensor. Differences between the bite patterns are detected at each phase of the induced fatigue. It is possible to compare the bite peak sensitivity coefficients for the exhaustion phase, 1.37 Ns-1 , and for fatigue phase, 2.54 Ns-1. Additionally, the increase in the facial thermal profile is correlated to the different bite force pattern performed.
This paper proposes an approach for lateral force sensing based on fibre Bragg gratings (FBGs) and Gaussian process regression (GPR). The monitoring system is based on FBG sensors embedded in a glass structure (load cell), which converts the external lateral force into axial strain along the fibre. Whilst the use of conventional peak detection techniques to retrieve the Bragg wavelength of the embedded FBG sensor can easily fail due to the FBG spectral distortions induced by the lateral force, the proposed GPR approach permits a direct mapping of the FBG spectral shape (including its peak wavelength and any observed distortion) into the applied lateral force. Experimental results validate the proposed approach, demonstrating highly accurate lateral force monitoring even in conditions with distorted FBG reflection spectra.
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