Fabrication of highly Ge-doped fibre couplers by fusion-tapering technique

The authors report the fabrication of fused fibre 2 x 2 couplers mode of singlemode fibre with a cladding highly doped with germanium. The typical insertion loss is similar to that of 2 x 2 couplers made of standard telecommunication fibre, i.e. < 0.1dB. The best isolation achieved to date is 25dB. This will enable the realisation of components such as grating assisted couplers that combine the fibre fusion-and-tapering technique with the Bragg grating writing technique.