Cross relaxation of Tm3+ in Ge-Ga-S glasses

Abstract

Tm3+- doped fiber amplifiers (TDFA) have been developed for a long time for fiber optics in S – band (1460 – 1530 nm). Such emission band originates from the transition of 3H¬4 to 3F4 level, however electrons at 3H4 states undergo rapid depopulation due to multiphonon relaxation to 3H5 states owing to small energy gap between those states ~ 4300 cm-1. Chalcogenide glass with low phonon energy have been employed as a suitable host matrix for incorporation of Tm3+. However it was reported that the solubility of Tm in various chalcogenide glass systems such as binary Ge-S, ternary Ge-As-S is very low. As a result, energy transfer among Tm ions i.e cross relaxation becomes significant, shortens upper state lifetime and limit the performance of the devices. To address this issue, Ga is added to the glass system and has been proven to substantially increase rare earth solubility in glass host matrix. However, there have been no detailed reports on the Tm concentration quenching and effects of Ga addition to overcome this issue. In our investigation, we report the concentration limit for cross relaxation of Tm occurring in different glass Ge-Ga-S series (GGS) with varying Gallium concentration to evaluate the effectiveness of Ga in dispersing Tm.