Thermal stability of self-organized gratings and defects in Geand Ge-P-doped silica core fibers

摘要

Thermal stabilities of photoinduced paramagnetic defects in second-harmonic (SHG) generation Ge-P-doped silica fibers and in Ge- and Ge-P-doped silica preforms are studied by electron-spin- resonance and compared with that of the reported self-organized gratings. Our data suggests that the charge trapping sites for the electric-field-induced SHG are Ge(1), Ge(2) and Ge E'$-d1$/ centers. The defects responsible for the Bragg gratings are Ge E'-type centers. Thermal darkening in Ge-doped silica core fibers reported is likely due to the thermal induced Ge E'$-d1$/ center.