Sensitivity enhancement of D-fibre methane gas sensor using high-index overlay

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Abstract
The authors determine that the sensitivity of a D-fibre methane gas sensor can be improved by overcoating the flat surface of the fibre with a high index layer. Using the finite-difference/perturbation theory technique, the enhancement factor over uncoated D-fibre is computed. The results compare favourably with those obtained from analytical expressions and the matrix method for a planar waveguide structure which models the overcoated D-fibre. From the oretical results it is concluded that the sensitivity can realistically be improved by an order of magnitude over an uncoated fibre.