Thermal stability of photoinduced gratings and paramagnetic centers in Ge- and Ge/P-doped silica optical fibers

Abstract

The electron-spin-resonance spectra of paramagnetic defects in Ge/P-doped silica fibers prepared with second-harmonic generation (SHG) are compared with those induced in Ge- and Ge/P-doped silica preforms by 5-eV photons. Among the defects observed, the thermal stability of Ge E'-type centers is similar to that of photoinduced Bragg grating efficiency but not of SHG efficiency. The isochronal anneal curves of the Ge(l) and Ge(2) centers in, Ge/P-doped silica correlate well with SHG efficiency, but the agreement is not nearly so good in silica containing only Ge. Only the thermal behavior of photoinduced Ge E'(d1) centers is similar to that of SHG efficiency in both materials, albeit only in the initial stages of annealing.