Investigation of the Writing Mechanism of Electric-Arc-Induced Long-Period Fiber Gratings

The mechanism for inscription of electric-arc-induced long-period gratings in SMF28 fiber was studied. The refractive-index profiles of irradiated fiber samples were measured, and their structures were investigated by Raman and luminescence spectroscopy. Slight geometrical deformations of the irradiated fiber were measured. A significant change in the Raman spectrum range from 200 to 700 cm^-1 caused by the electric arc is reported. The results show a decrease in the intensity of this band, indicating a modification, such as densification, of the glass structure. No modification of the fictive temperature was measured. A large increase in the red luminescence band was also observed and attests to the creation of defects in the fiber network structure.