The Letter demonstrates how the sensitivity of D-fibre based sensors depends on its parameters (refractive index difference, core diameter and flat surface-core distance). The optimal fibre parameters are predicted using the authors' finite difference/perturbation theory model, and similar results were obtained using a ray optics method for the planar wave-guide to model the D fibre. It is concluded that the D fibre within its optimum architecture exhibits relatively low sensitivity. This sensitivity can however be improved using a suitable overcoating.
