Low-loss joints between dissimilar fibres by tapering fusion splices

A technique is reported for reducing the splice loss between dissimilar or similar fibres. The technique involves tapering a fusion splice to produce a mode transformer which converts the fundamental mode of one fibre to that of the other with negligible loss. Results of theoretical calculations are presented which show the fundamental mode field shape at the splice junction and the estimated joint loss between two dissimilar fibres as a function of the splice diameter. Initial experiments are reported which have achieved splice loss reductions from 1.5 dB to 0.56 dB and 0.7 dB to 0.15 dB between dissimilar and similar fibres, respectively, at 1.3 ?m.