Fabrication and characterization of long period gratings in pure-silica fibers

Abstract

The recent results about the fabrication and characterization of Long Period Gratings (LPGs) in different pure silica optical fibers by means of Electric Arc Discharge (EAD) technique are reported in this work. Nowadays, LPG in standard fiber represents a unique platform for physical, chemical and biological sensing whereas specialty optical fibers permit to extend the use of fiber optic technology to unconventional applications. For instance, pure silica fibers are appealing in high energy applications. Here, we take into consideration two fibers with pure-silica core having significant differences in physical and geometrical design. The first one presents a micro-structured pure-silica cladding, photonic crystal fiber, and the second one shows a solid Fluorine-doped cladding. EAD leads to a point-by-point LPG inscription, due to localized tapering of the transversal size of the core and cladding regions along the fiber, and to changes of the silica refractive index due to the stress relaxation induced by local hot spots. The aim of the work is to identify an appropriate “recipe” for each fiber, to fabricate LPGs with strong and narrow attenuation bands and trivial power loss. Indeed, a proper combination of arc power and duration, as well as fiber tension, allows for the appropriate core and cladding modulation and thus for the desired LPG spectral features. The sensitivity characteristics towards surrounding refractive index (SRI) and temperature changes of these LPGs are also investigated.