Evanescent field fiber-optic sensors for humidity monitoring based on nanocoatings

The transmitted optical power of two different fiber optic based structures when a nanofilm is being deposited onto them is experimentally studied. The technique used to build the nanofilms is Electrostatic Self Assembly (ESA), which has been widely reported in the literature. For the shake of comprehensibility, the comparative analysis of this phenomenon is accomplished for a particular sensing measure, humidity. The two structures selected towards development of practical humidity evanescent field sensors are hollow core fibers and tapered optical fibers. Some preliminary experimental studies of depositing humidity sensitive thin films and demonstrating their feasibility are presented. Depending on the working point selected, up to 10 dB of variation in the optical output power is obtained when the environmental humidity changes. Both configurations exhibit similar dynamic behavior and response times shorter than 300 msec, making these evanescent field sensors good candidates to monitor human breathing.