Long Period Gratings Inscribed With Electric Arc in Nanostructured Optical Fibers and Their Sensitivity to Gamma Radiation

In this work, for the first time, we demonstrate long period gratings (LPG) in nanostructured optical fibers and their response to gamma radiation. Nanostructured fibers show distinctive features such as arbitrary gradient refractive index (RI) distributions in the core, core shapes without symmetry constraints, and engineered polarization properties as an intrinsic feature of the artificial glass material. Two nanostructured silica single mode optical fibers have been processed using the electric arc discharge technique to inscribe LPGs and the results have been compared with those for standard Ge-doped SMF28. The core of the first fiber shows a parabolic RI profile achieved arranging high-RI nanorods. The second fiber contains a core composed of silica and ytterbium-doped silica nanorods arranged as alternating layers of high- and low-RI (i.e., in a “ZEBRA” structure). First, a detailed analysis of the LPG formation during the inscription, polarization dependence and response to surrounding RI, temperature, and strain have been provided. Moreover, the impact of a 30 kGy gamma radiation dose has been evaluated in real time on these nanostructured fibers by monitoring the resonance wavelength shift. It has been found that nanostructured fibers can be effectively processed with electric arc towards LPG inscription in similar manner as standard fibers. Moreover, in the case of ZEBRA fiber a high sensitivity to gamma radiation can be obtained.