Local supermode analysis of tapered fibre sensor

The authors investigate the performance of an evanescent-field fibre sensor made from standard single-mode optical fibre with a tapered cladding region, upon which a thin attenuating material coating is deposited. The authors´ method involves calculating the supermodes of the complete core-cladding-coating-air structure locally at each point along the taper and studying the evolution of the supermode guided power along the sensor. Results are compared with those from numerical finite difference scheme; and also used to interpret experimental results obtained for a taper with a thin layer of sulphur deposited by electrical discharge in an atmosphere of SF₆