Long Period Fiber Grating Sensors Fabricated by Electric Arc Discharge Technique

This work reports about the fabrication and characterization of Long Period Gratings (LPGs) sensors in pure silica core optical fibers having significant differences in physical and geometrical design, by means of Electric Arc Discharge (EAD) technique. 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. LPG in standard fiber is well known for its physical, chemical and biological sensing while specialty fibers permit to widen the horizon of application of fiber optic technology towards unconventional field of research. For instance, pure silica fibers are extensively appealing in high energy and space applications. This work aimed at identifying an appropriate “recipe” for each fiber, to fabricate LPGs with strong and narrow attenuation bands, trivial power loss supported by smaller grating length. Hence, a suitable combination of arc power, arc time, fiber tension and electrodes gap, is a must for the appropriate core and cladding modulation and in turn for the desired LPG spectral features. Finally, the surrounding refractive index (SRI) and temperature characterization of these LPGs were performed to investigate the sensitivity features.