Development of praseodymium-doped, selenide chalcogenide glass, step-index fibre towards mid-infrared fibre lasers

Chalcogenide glasses are promising materials for mid-infrared (MIR) fibre optic applications i.e. 3-25 μm wavelength. Their low phonon energy is attractive not only for passive mid-IR transmission fibre-conduits but also for active fibre. For the latter, rare earth (RE-)-ion doped chalcogenide glasses have been investigated, as direct emission mid-IR fibre lasers. The quality of the chalcogenide glass fibre is key to this application. RE-ion addition to the chalcogenide glasses can lead to devitrification. Gallium has been identified as a useful additive to help successfully solubilise the RE-ions and it is thought that gallium complexes the RE-ions in the glass matrix. We investigate here replacing gallium with indium. Indium shares Group 13 of the New Periodic Table with gallium and so exhibits similar chemical behaviour. Indium is heavier than gallium, potentially promoting lower phonon energy locally at the RE-ion. We have found enhanced fluorescence behaviour of the RE-ion in bulk glasses formulated with indium rather than gallium. Here, drawing of step index fibre (SIF) based on ~ 500 ppmw (parts per million by weight) Pr³⁺-doped Ge-As-(In or Ga)-Se chalcogenide glasses is successfully carried out. MIR fibre loss of the Pr³⁺-doped SIFs is measured as well as fibre photoluminescence in the range 3-6 μm.