Nonadiabatic tapered single-mode fiber coated with humidity sensitive nanofilms

A new humidity sensor has been developed by coating a tapered single-mode standard communications fiber with a humidity sensitive nanofilm using the electrostatic self-assembled (ESA) monolayer technique. Power changes up to 20 dB have been recorded during the coating process. In order to take advantage of both the potential sensitivity of the tapered fiber and the precise thickness control, which is possible to achieve using the ESA technique, the optimal layer thickness has been adjusted to the maximum slope point of the transmitted optical power curve as a function of the overlay thickness. An optimal working point sensor is compared to a nonoptimal one demonstrating the sensitivity difference between both.