Etched Saturated Fiber Bragg Gratings for Refractive Index Measurements

This work presents the results of the production and characterization of etched saturated fiber Bragg gratings (ESFBGs) functionalized with gold nanoparticles (AuNPs) as a refractive index sensor. Saturated fiber Bragg gratings (FBGs) are produced by directly exposing the phase mask to the laser beam to generate the interference pattern in a hydrogenated fiber. An iris with variable diameter is used to select the central portion of the laser beam; 2 and 4 mm diameters are used to inscribe the gratings. ESFBG exhibits sensitivity over a broader range of refractive indices and a reflection spectrum with greater intensity, even after the deposition of AuNPs on the fiber, and coupling to the HE12 mode with greater sensitivity. The results show that the ESFBG inscribed with the iris opening of 4 mm presented the greatest range of refractive indices possible to be measured. These characteristics show that the ESFBG is a good option for refractive index sensors in which power loss is a limiting factor.