Fabrication of Er3+-doped fluoride fibres with single-mode geometry based on over-clad drilling

Fluoride preforms with single-mode geometry have been accomplished by drill ing a small hole along the centre axis of an over-clad rod and inserting an Er3+-doped multimode preform stretched. From such preforms, single-mode fi bres have been drawn, which could be used for the fabrication of optical am plifiers. Core-clad concentricity of the fibres depended on the precision o f the drilling operation. Best fibres have a core non-circularity of 5.9%, a clad non-circularity of 3.3% and a core-clad concentricity of 1.7 mu m. F ibre loss and bending strength were measured to be 0.48 dB/m and 0.83 GPa, respectively, (C) 1999 Elsevier Science B.V. All rights reserved.