Development of germanium gallium sulphide glass fibres for the 1.31 μm praseodymium doped fibre amplifier

We report on our current progress in the development of germanium gallium sulphide glass fibres for the praseodymium-doped fibre amplifier (PDFA). Praseodymium-doped glasses with compositions (GeSx)98(GaS3)2(x: 2.25, 2.5, 3) are melted from germanium and gallium metals and sulphur in sealed silica ampoules at 1000°C and then quenched in air. The critical step in the fibre manufacturing process is the fabrication of the fibre preform out of glass rods. The 'rod in tube' method was selected for preform fabrication. A new hot deformation process for manufacturing cladding tubes using the visco-elastic properties of the glass is described. A measure for the thermal stability of the glasses is the difference between the glass transition temperature, Tg, and the crystallisation onset temperature, Tx. The thermal stability was evaluated using dilatometry and combined differential thermal analysis/thermogravimetry (DTA/TG) analysis for determining Tg and Tx. For the selected germanium gallium sulphide glasses the difference between the crystallisation temperature and glass transition temperature is more than 200°C. Both the fibre drawing temperature and the hot deformation temperature (to produce cladding glass tubes) are less than the crystallisation onset temperature. The germanium gallium sulphide host glasses are transparent in the 0.5-10 µm wavelength region. The wavelength of the maximum of the stimulated emission band with full width at half maximum (FWHM) amplitude of 80 nm is 1.34 µm, the emission lifetime is 390 µs.