Hybrid-cavity fabry-perot interferometer for multi-point relative humidity and temperature sensing

A novel hybrid-cavity Fabry-Perot interferometer (HFPI) is theoretically proposed and experimentally demonstrated. The hybrid micro-cavity structure is consisted of a short segment of four-hole suspended-core fiber (SCF) and attaching moderate optical adhesive as the hygroscopic material. Due to the different sensitivities of the hybrid Fabry-Perot (F-P) cavities to the relative humidity (RH) and temperature, both information can be simultaneously demodulated by utilizing the phase-shift tracking scheme in the Fast Fourier Transform (FFT) spectra. The precise micromanipulation of each cavity length ensures the separation of each amplitude peak in the FFT spectra, which renders this HFPI multi-point sensing capability. Experimental tests were carried out, and the results indicate that the proposed HFPI with excellent sensing performance is a promising platform for multi-point RH and temperature sensing applications.