Ultraviolet-induced paramagnetic centers and absorption changes in singlemode Ge-doped optical fibers

Abstract

We investigated the laser-energy-density dependence of absorption changes and paramagnetic centers induced by a cw Ar(+)laser operating at 5.1 eV, in both unloaded and H(2)-loaded singlemode Ge-doped optical fibers. The induced absorption is measured in the blue and near ultraviolet spectral range by using the 3.1 eV photoluminescence, ascribed to Ge lone pair center (GLPC), as an in situ probe source. We find that the Ge(1) center (GeO-(4) ) is induced upon UV exposure by electron trapping on GeO(4) precursors, where the free electrons are most likely produced by ionization of GLPC. Ge(1) is responsible of optical transmission loss of the fiber in the investigated range. Hydrogen loading strongly influences the generation efficiency of the several observed paramagnetic defects, leading in particular to passivation of radiation-induced Ge(2) centers.

Radiation hardening of silica glass through fictive temperature reduction

“…Similar measurements performed with 1 mW power and 3.0 G of modulation amplitude are shown in Figure B. It can be seen that two kinds of doublet centers with a magnetic field separation of 74 G and 119G are the signature of H(I) and H(II) defect centers, respectively . The remaining components of the signal above g =1.99 can be attributed to the hyperfine structure of aluminum oxygen hole centers (AlOHC) .…”

“…The formation of H(I) doublet is a result of the hyperfine interaction between the unpaired electron of SiE’ centers and a proton of a hydrogen (H 2 ) molecule which is substituting a nearest neighboring oxygen of dangling Si bond . The H(II) defect can occur generally in two ways, either twofold coordinated germanium reacted with H 0 in ground state or by direct reaction of H 2 with twofold coordinated germanium in the excited‐triplet state . It is important to note that the concentration of H(I) and H(II) defect centers drastically increase with an increase of fictive temperature.…”

Paramagnetic germanium-related centers induced by energetic radiation in optical fibers and preforms

“…4 allow us to spatially localize the optically active centers: they are mainly concentrated in the inner core zones with larger Ge content. Earlier studies [2,5,16,17] have clarified that an OA band centered at 4.5 eV with full width at half maximum of $1.5 eV is correlated to the Ge(1) EPR signal. It is worth noting that these spectral parameters are in good agreement with those obtained by our best fitting procedure reported in Fig.…”

“…The research interest is mainly motivated by the practical importance of these materials in photonic applications, from standard optical fibers as waveguides for telecommunications to non-linear optical devices [1]. This multi-use of Ge-doped silica is strongly influenced by its response to radiation; for instance, it is known that radiation exposure induces Ge-related defects that are cause of attenuation for the waveguides, thus leading to detrimental losses of part of the transmitted signals [3][4][5][6]. The identification of the specific defects, sensitive to radiation, is therefore of crucial importance to make clear the microscopic origin of technologically relevant processes.…”

Optical absorption induced by UV laser radiation in Ge‐doped amorphous silica probed by in situ spectroscopy

“…Many studies have evidenced that laser exposure of Ge-doped silica is able to induce transparency loss, photosensitivity and optical nonlinearity in the material, related to generation and conversion of point defects triggered by laser light and highly interesting from an applicative point of view [1][2]. These processes have been extensively studied with multiple spectroscopic techniques, such as optical absorption (OA) and electron spin resonance (ESR) but many questions still remain open [3][4][5][6][7][8][9]; in particular, their kinetics during and after laser irradiation has not been sufficiently investigated, due to the lack of appropriate in situ techniques, which allow to evidence transient features of the spectroscopic signals inaccessible to ex situ observation. Also, the attribution of the absorption bands to the known Ge-related defects is still an open problem.…”