Abstract

Progress in applications of photosensitivity of silica glasses for fabrication of reflection optical fiber gratings is restrained by an obscurity of nature of photorefractivity of the glasses. There is a lot of inconsistent interpretations of spectral properties of oxygen deficient centers (ODC) responsible of UV absorbance of the glasses. Photoinduced refractive index variations of the glasses are in accordance with Kramers- Kronig relation due to the absorbance changes. As much as ~ 10^-4 photoinduced index variation of Ge- doped silica at 1.5 μm is for instance explained by photobleaching of 5.1 eV spectral band and increasing of absorptivity of 6.5 eV band [1]. However experimentally obtained index changes larger than 10^-3 are probably caused by changes of the absorbance at shorter wavelengths corresponding to energy gap transitions and consequently accompanied by modification and compaction of glass matrix [2]. In this work, the interpretation of ODC optical spectra of SiO₂ and SiO₂:GeO₂ glasses is discussed and model of the solid-state photoinduced chemical reactions is proposed to explain the start-up of physical and chemical processes of varying of ODC concentrations and macroscopic parameters of the glasses which is confirmed by the analysis of ODC preparation technique.

© 1995 Optical Society of America