Fabry-Perot Interferometer Based on Etched Side-hole Fiber for Microfluidic Refractive Index Sensing

In this paper, we present a novel fiber-optic open-cavity Fabry-Perot interferometer (FPI), which is specially designed for microfluidic refractive index (RI) sensing. An etching Side-hole fiber (SHF) was sandwiched between in two single-mode-fibers (SMF) and then a cavity was opened up by chemical etching method in the SHF. The minute order of the etching process endow such FPIs with low cost and ease of fabrication. For further microfluidic sensing test, the FPI was integrated with a cross microfluidic slit that was fabricated through photolithography. The refractive index response of the FPI was characterized using sodium hydroxide solution with RI range from 1.3400 to 1.3470. Experimental results show that FPIs with different length of open-cavity have the similar liner RI response with different RI sensitivities. The optimal RI sensitivity of more than 1138 nm/RI can be achieved with open-cavity length of 56 mu m. The temperature response was also investigated, which shows that FPIs exhibit a very low temperature cross-sensitivities of 4.00 pm/degrees C and 1.95 pm/degrees C corresponding FPIs with cavity length of 123 mu m and 56 mu m, respectively. Such good performance renders the FPI a promising in-line microfluidic sensor for temperature-insensitive RI sensing.