Polarization dependent gain in Pr3+/Yb3+ doped fluoride fibre

Fibre amplifiers and lasers are formed by introducing rare-earth ions into silica and fluoride fibre material. The advantage of fluoride glasses is the much more efficient upconversion lasing in co-doped systems such as the Praseodymium/Ytterbium system used in this work. We investigate the gain properties of Pr³⁺/Yb³⁺ doped fluoride fibres with the ultimate goal of developing a blue polarized fibre laser. When a probe with state of polarization parallel to the major axis of the elliptical fibre core is injected, no rotation of its output polarization is observed with pump injection and a higher gain is achieved for a given pump power. Moreover if both probe and pump polarization are aligned with the major axis, the onset of the gain is found to occur at lower pump power.