Er3+-doped GeGaSbS glasses for mid-IR fibre laser application:: Synthesis and rare earth spectroscopy

With an infrared transparency extended to 10 pm, low multiphonon relaxation rates and suitable rare earth solubility, sulphide glasses in the Ge-Ga-Sb-S system allow radiative emission from rare earth ions in the mid-IR range. The Er3+ ion, widely studied in glass fibres for optical amplification at 1.5 mu m, presents an interesting transition for mid-IR applications around 4.5 mu m (I-4(9/2) -> I-4(11/2)). Thus, the aim of this work is to evaluate the Er3+-doped Ge20Ga5Sb10S65 glass as a potential fibre laser source operating in the 3-5 mu m mid-IR spectral region. For that purpose, absorption and emission spectra were recorded from visible to mid-IR and the radiative lifetimes of the involved excited levels (I-4(9/2), I-4(11/2) and I-4(13/2)) were determined. Experimental results were compared with those obtained from a Judd-Ofelt analysis based on the absorption cross-sections of all observable transitions. The I-4(9/2) radiative quantum efficiency was estimated to be 64% and the emission cross-section at 4.6 mu m was found equal to 2.85 x 10(-21) cm(2). Core only and core/clad Er3+-doped Ge20Ga5Sb10S65 glass fibres were successfully drawn with minimum optical losses of about 1.5 and 10 dB/m at 5.2 and 3.5 mu m, respectively. Fluorescence signals in the mid-IR (at 2.7 and 4.6 mu m) were clearly observed with both fibres. (c) 2008 Elsevier B.V. All rights reserved.