Multiplexing of fiber Fabry-Perot interferometer for multi- point refractive index sensing application

We proposed a multiplexing method of optical fiber Fabry-Perot interferometer (FPI) for multi-point refractive index (RI) sensing application. This method is based on the frequency modulated continuous wave (FMCW) interferometry, in which a series of FPIs are connected by fiber couplers as like the bus-structure. Due to the spatial difference among FPIs, the reflection signals from different FPIs can be separated in spatial domain by Fourier transform. Applying inverse Fourier transform, the interference spectra of every FPIs can be demodulated independently in wavelength domain. Three FPIs are multiplexed for verifying the multi-point RI sensing ability of the proposed method. The experimental results show that the proposed multiplexing method performs well in multi-point RI sensing applications. In the RI range of 1.3334 similar to 1.3410, the RI sensitivities of the multiplexed FPIs are as high as 1200 nm/RIU, and the RI measurement accuracies are as high as 5x10(-6) RIU. In addition, the sensing system can demodulate the interference spectrum from the reflected signal as low as 5 pW. When the light source power is 3.2 mW, the theoretical maximum multiplexing number is 8000. This work provides an efficient solution for multi-point RI sensing.