Improved Temperature Sensitivity of Tapered Fiber Bragg Gratings for Biomedical Applications

Temperature sensing is extremely important factor for many biomedical applications toward a prompt and accurate medical control and examination. The purpose of this work is to investigate theoretically the design of novel single mode tapered fiber Bragg gratings (TFBGs) with maximum temperature sensitivity to be used in biomedical field. The parameters which govern the functionality of TFBGs were studied in order to optimize the temperature sensitivity. Coupled mode theory (CMT) and transfer matrix method were applied to analyze TFBG structure. A numerical analysis was performed to investigate the mechanical properties of TFBGs and the cladding diameter on temperature sensitivity. Herein, the TFBGs are assumed to a reflection Bragg wavelength around 1550 nm and are inscribed in single mode fiber (Corning SMF-28). The results show that the temperature sensitivity of TFBGs at optimized parameters could reach \(14.83\, \mathrm { pm/^\circ C}\) $14.83\mathrm{pm}{/}^{\circ }\mathrm{C}$ , which is superior to those of conventional fiber Bragg gratings with the same parameters ( \(\sim 11.87 \, \mathrm {pm/^\circ C}\) $\sim 11.87\mathrm{pm}{/}^{\circ }\mathrm{C}$ ). Moreover, the effect of taper ratio on sensitivity was investigated in this study. The findings also demonstrate that the sensor sensitivity can be adjusted with variation to the taper ratio. From the results, it is confirmed that the sensitivity of TFBGs was improved by reducing linearly the fiber diameter up to 15 μm compared to uniform FBGs ones, achieving the highest temperature sensitivity.