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

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