Comparison of formation process of ultraviolet induced color centers in GeO 2SiO 2 glass fiber preform and Ge-implanted SiO 2

Abstract

Photochemical reactions induced by ultraviolet (UV) excimer lasers were investigated for a 10GeO 290SiO 2 (mol%) glass fiber preform and a SiO 2 glass implanted with Ge + ions (1 × 10 16 cm −2) by the electron spin resonance (ESR) and the optical absorption. Electron trapped centers associated with fourfold coordinated Ge ion (GEC) were formed in the former by irradiation with KrF laser (5 eV) or ArF (6.3 eV) laser pulses. The concentration of GECs increased as the square of the laser power, which means that the formation reaction of GEC proceeds via a two-photon absorption process. Si E′ centers (·SiO 3, full width at half maximum (FWHM) = 3 G) and peroxy radicals (PORs: SiOO · or O 2 −) we formed in the SiO 2 glass implanted with Ge ions, which could be bleached by UV irradiation or prolonged isochronal annealing. The exposure of the annealed glass to excimer laser pulses induced Si E′ centers having identical FWHM with that observed in the as-implanted glass. No UV-induced ESR signal related with Ge ion was confirmed before or after annealing. The intense UV absorption bands were induced both in fiber preform and implanted glasses, which should cause the positive index change.