Design of Planar Optic Sensors for Hydrocarbon Detection

A realistic design of evanescent field optical sensors, constituted by three different kinds of planar waveguides covered by a sensing polymeric overlay, is performed. More precisely, the slab, the embedded strip and the ridge waveguides are considered. The sensor operation is simulated, in both the cases of lossy guided and leaky mode propagation, via a home made computer code. The optimal waveguide transverse section and length are identified, the advantages and drawbacks are shown. The ridge waveguide sensor exhibits appreciable characteristics: for a concentration C-w = 200 ppm of toluene in water, the absorbance pertaining to a device L = 2.6 cm long and for the guided quasi-TEinfinity mode is A congruent to 5, while it is A congruent to 0.054 for a device long L congruent to 24.1 mum and the leaky quasi-TE10 mode. The simulation results suggest that a selective excitation of the suitable propagation mode can enhance the sensor performance.