HEC/PVDF coated microbottle resonators for relative humidity detection

A micro-bottle resonator sensor is proposed here for relative humidity detection with an HEC/PVDF coating acting as a transducer. Microbottle resonators are a promising fiber optics sensing structure due to their high-quality factor and HEC/PVDF is used in detecting relative humidity due to its sensitivity to moisture and humidity. Soften-and-compress technique was used to form a 190 μm bulge micro-bottle sensing element. A 3 μm tapered microfiber was used to optically excite the micro-bottle resonator which showed a Q factor in an order of 10⁵. The HEC/PVDF coated MBR resonator sensor showed good response to changes in relative humidity range of 40–80 %RH. The HEC/PVDF coated element had a sensitivity of 0.111 dB/RH% and linearity of 95 %. The HEC/PVDF absorption of water molecules with increasing relative humidity, the subsequent change in refractive index and change in the light propagation characteristics of the sensor improved the sensor's response to relative humidity compared to the uncoated one. The proposed sensor's simple fabrication, good sensitivity, linearity, and resolution make it a promising design for relative humidity detection.