Concave cone fabricated by a chemical etching process similar to the technique used to make fibre tips (convex cone) is presented. Typically, optical fibres are etched in a hydrofluoric (HF) solution with a thin layer of oil floating on top of the HF solution. The present investigation shows that concave cone etched fibre (CCEF) can be obtained by following the beginning of the etching process. Comprehensive measurements of the dependence of the width and height of the taper angle of the concave cone are plotted. The results of this investigation have led to an optimum approach for core fibre alignment that is suitable for use in connecting fibres for efficient coupling between single-mode fibres.

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