Backscattering Analysis of UV Radiation in NP-Doped Fibers: Toward Grating Inscription

This article presents the analysis of UV radiation in nanoparticles (NPs)-doped fibers aiming at the development of fiber Bragg gratings (FBGs) in such fibers using the phase mask inscription method. In this case, the UV radiation is applied on the NP-doped fiber at different inscription times and energies. As a new approach for the inscription analysis, the cross correlation of the backscattering signals before and after the UV radiation is analyzed using an optical backscattering reflectometer (OBR) for time and frequency domains, where it is possible to observe a spectral shift on the region of the UV inscription. Such spatially resolved spectral shift is due to localized refractive index variations along the fiber and can be used for the assessment of refractive index modulation on the grating region. Following this method, it is possible to observe a threshold of 3 min for the UV inscription at 100-Hz repetition rate and 3.16-mJ energy for the FBG formation in NP-doped fibers. In addition, the strain responses of the NP-doped fiber are analyzed under different UV radiation conditions, namely, no radiation, radiation below threshold for grating formation, and the radiation above the threshold, where such conditions are compared with the standard single-mode fiber (SMF) under the same UV radiation conditions. The results show a threefold increase in strain sensitivity when the NP-doped fiber is compared with the SMF. Furthermore, it is possible to observe an increase on the spectral shift sensitivity when the UV radiation is applied above the threshold to FBG formation.