Behaviour of asymmetric fuse-tapered single-mode fibre couplers

Fused-tapered single-mode fibre couplers which have a flattened wavelength response useful in applications requiring a near-constant power-splitting ratio over a range of wavelengths. They are made by inducing an asymmetry in the constituent fibres. The authors demonstrate that the maximum coupled power of an asymmetric coupler is strongly dependent on the degree-of-fusion in the coupler, and that it is possible to obtain near-total power transfer (or indeed any level of power transfer) for a given cladding diameter asymmetry by controlling the degree-of-fusion of the coupler. They therefore remove the requirement for a controllable differential etching process prior to coupler fabrication