Otimização da sensibilidade à pressão de fibras de bandgap fotônico

Abstract

This work deals with the study of the sensitivity to pressure and temperature of photonic crystal fibers aiming at applications in distributed sensing. Although PCFs allow for distributed measurement, just as conventional fibers do, this type of measurement has been little exploited, especially for pressure sensing and using all-solid fibers with guidance via a photonic bandgap (AS-PBGFs). The aim of this work is to propose, by means of mechanical/optical coupled numerical simulations, a new design for an AS-PBGF whose transmission and birefringence are sensitive to pressure variations. A conventional AS-PBGF was analyzed, showing low transmission sensitivity to pressure (~2.7 x 10-4 dB/(bar.m)) and no phase birefringence. So we proposed a modified AS-PBGF, with the inclusion of four air holes around the core, and the second and third bandgaps of this fiber were studied. At the center of the second bandgap (λ = 1.53 μm) transmission presented, for the x and y polarizations, the same behavior when submitted to ambient temperature variations; and opposite behavior when submitted to pressure variations, making it possible to distinguish betweeen the impact of these two quantities. On the other hand, the center of the third bandgap (λ = 0.93 μm) showed appreciable birefringence sensitivity to pressure (- 3.05 x 10-7 1/bar at 200 bar), which is higher than that presented in the literature (- 1,346x10-7 1/bar). At this spectral position, the low birefringence sensitivity to temperature (- 5.02 x 10-8 1/°C at 100 bar) compared with values found in the literature (- 1.362 x 10- 7 1/K), makes it possible to neglect temperature oscillations, which induce relatively small errors in the monitored pressure (induced error of ~10 bar for a temperature variation of 50 ° C).