Technique for reducing fibre joint loss

A method of forming an optical fibre joint between fibres of different refractive index profiles, which includes tapering adjacent end portions of the fibres to be joined such that at least a proportion of the optical energy which is normally guided in the fibre core is guided by the cladding of the fibres, at least in the waist of the tapered region.

A method of improving a joint between two generally co-axial optical fibres of different refractive index profiles, said method comprising the steps of heating the joint region so that it softens and whilst it is soft pulling the joint region so that the adjacent end portions of the fibres become tapered sufficiently that at least a proportion of the optical energy which is normally guided in the fibre core is guided by the cladding of the fibres, at least in the waist of the tapered region.

A method of forming a low loss optical fibre joint between first and second mono-mode optical fibers having respectively different refractive index profiles defining their respective cores and claddings and therefore exhibiting respectively different fundamental modes of optical propagation via their cores, said method comprising:

• fusing a free end of said first optical fiber coaxially to a free end of said second optical fiber;
• and
• thereafter drawing apart the fused ends of said fibers so as to simultaneously taper the joined ends to reduced diameter waist sections at the joint sufficiently to cause optical energy passing through the joint to be guided by the claddings of each fibre rather than by the cores of each fibre in said waist sections whereby optical signal propagation in a first mode along the core of said first fibre is transformed during passage along said waist regions into optical signal propagation in a different second mode along the core of said second fibre.