Optical Based Humidity Sensor by Using Zinc Oxide-PVA In Micro Cavity

Abstract

We demonstrate a simple optical based humidity sensor using a micro cavity. The micro cavity consists of single mode fiber (SMF-28e, Corning) and a reflective mirror coated with zinc oxide (ZnO) which is embedded in polyvinyl alcohol (PVA). A wideband amplified spontaneous emission (ASE) source, ranging from 1530-1610 nm was injected into the micro cavity. The water molecules from the surface of the ZnO-PVA changed the refractive index of the micro cavity which subsequently modified the phase of ASE light that was reflected from the coated mirror. The change of phase in the reflected light from the coated mirror was monitored with optical spectrum analyzer (OSA). The performance of our optical humidity sensor for non-coated mirror and ZnO-PVA coated mirror was recorded at 0.03 nm/RH% and 0.074 nm/RH%, respectively. This shows that optical humidity sensor with ZnO-PVA coated mirror is more sensitive to humidity changes.