Er 3+-doped GeGaSbS glasses for mid-IR fibre laser application: Synthesis and rare earth spectroscopy

Abstract

With an infrared transparency extended to 10 μm, 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 Er 3+ ion, widely studied in glass fibres for optical amplification at 1.5 μm, presents an interesting transition for mid-IR applications around 4.5 μm ( 4I 9/2 → 4I 11/2). Thus, the aim of this work is to evaluate the Er 3+-doped Ge 20Ga 5Sb 10S 65 glass as a potential fibre laser source operating in the 3–5 μm 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 ( 4I 9/2, 4I 11/2 and 4I 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 4I 9/2 radiative quantum efficiency was estimated to be 64% and the emission cross-section at 4.6 μm was found equal to 2.85 × 10 −21 cm 2. Core only and core/clad Er 3+-doped Ge 20Ga 5Sb 10S 65 glass fibres were successfully drawn with minimum optical losses of about 1.5 and 10 dB/m at 5.2 and 3.5 μm, respectively. Fluorescence signals in the mid-IR (at 2.7 and 4.6 μm) were clearly observed with both fibres.