Relative Humidity Sensor Based On An Optical Microfiber Knot Resonator With A Polyvinyl Alcohol Overlay

A highly sensitive RH sensor based on the MKR with the PVA overlay is investigated. After making a tie using the microfiber with a diameter of 2 mu m, the MRK with a loop diameter of 90 mu m is fabricated and coated by using a PVA which can absorb humidity. The optical spectra of the MRK with the PVA overlay are converted to the spatial frequency spectra by using the FFT for precise measurement. The absorption of humidity in the proposed MKR-based sensing probe effectively changes the spatial frequency of the MKR. The RH sensitivities of the proposed MKR-based RH sensing prober with higher order modes can be dramatically improved.