A PMMA microfiber loop resonator based humidity sensor with ZnO nanorods coating

A Polymethyl methacrylate (PMMA) microfiber loop resonator (PMLR) coated with zinc oxide (ZnO) nanorods is proposed and demonstrated for the monitoring of relative humidity (RH) of the surrounding air. Relative humidity refers to the amount of moisture in the air relative to the total amount of moisture that the air can contain. The PMLR has a loop diameter of 42 μm and was fabricated using a direct drawing technique using an 8 μm diameter PMMA microfiber. The results showed an increase in the sensitivity of the sensor with the additional coating of the ZnO nanorods on the surface of the PMMA fiber. The working mechanism of the device is based on the observed increment in the transmission of the sensor that was carefully placed in a sealed chamber. As the relative humidity level increases from 50%RH to 80%RH, the output power of the PMLR with ZnO nanorods coating decreases linearly from −37.77 dBm to −52.99 dBm with a maximum sensitivity, linearity and resolution of 0.5221 dBm/%RH, more than 99% and 0.4094%RH, respectively. This work is highly beneficial as it combines the high sensitivity of traditional silica fibers with the ruggedness and flexibility of PMMA fibers, making them highly suitable for continuous monitoring of relative humidity in compact areas.