Characteristics of LPFGs Written by a CO2-Laser Glass Processing System

This paper presents the characterization of the response of CO
₂
-laser induced LPFGs by using a glass-processing system. The symmetric perturbation induced by the process is a result of the tapering of the fiber cladding and diffusion of the fiber core. The core diameter is increased from 8.4 to 13.8 μm at the waist of the taper as obtained from SEM microscope images of the fiber end. Sensitivity to temperature, strain, and bending was 101.2 pm/°C, -1.05 pm/με, and -17.74 nm/m
^-1
, respectively. Application to the measurement of glycerol-distilled water and gasoline-alcohol solutions was realized, resulting in the last case, in a sensitivity of 514 pm/percent of gasoline in alcohol. A simulation that accounts for dispersion material, core diffusion, cladding tapering, and stress release closely reproduces the unperturbed transmission spectrum; however, it only can reproduce the response to changes in the external refractive index of LPFGs fabricated and measured under specific conditions explained in the text. The study presented in this work is essential for considerations on the stability that the LPFGs must have in order to be useful for practical applications.