Mid-infrared fiber laser application: Er3+-doped chalcogenide glasses

Abstract

Mid-infrared (IR) lasers are of interest for a variety of applications including environmental sensing, LIDAR and military counter measures. However, this wavelength range lacks powerful, coherent, robust and compact sources. A solution can lie in chalcogenide glasses as host materials for rare earth ions. With an extended infrared transparency, low phonon energy limiting the non radiative multiphonon relaxation rates and suitable rare earth solubility, sulfide glasses based on Ge-Ga-Sb-S system make available radiative transitions in the mid-IR range. The glasses with nominal composition of Ge₂₀Ga₅Sb₁₀S₆₅ doped with Er³⁺ (500 to 10000 ppm) were prepared by means of conventional melting and quenching method. The Er³⁺, widely studied in glass fibers for near-IR amplification, was initially selected for the transition ⁴I_9/2 to ⁴I_11/2 emitting at around 4.5 &mgr;m in order to demonstrate the ability of this sulfide composition for midinfrared fiber lasers application. In these objectives, absorption and emission spectra have been recorded and the radiative decay lifetime of excited levels (⁴I_9/2, ⁴I_11/2 and ⁴I_13/2) has been determined. These last experimental results were compared with those obtained by Judd-Ofelt model from absorption cross-sections of all observable transitions. Therefore, the ⁴I_9/2 radiative quantum efficiency was estimated at 67 %. The emission cross-section was 2.6x10^-21 cm² at 4.6 &mgr;m obtained by Fütchbauer-Ladenburg theory. The product of measured lifetime and emission cross-section for ⁴I_9/2 -> ⁴I_11/2 transition is about 1.87x10^-24 cm².s is comparable with that for GaLaS glasses. The fiber drawing of the Er³⁺ doped Ge₂₀Ga₅Sb₁₀S₆₅ glasses and measurements of optical losses in mid-IR are currently in progress and first results were presented.