Novel Compact and Low-Cost Ultraweak Fabry–Perot Interferometer as a Highly Sensitive Refractive Index Sensor

A novel compact refractive index (RI) sensor based on an ultra-weak intrinsic fiber Fabry-Perot interferometer (FPI) is proposed and demonstrated, which is simply fabricated by splicing a tiny section of thin-core fiber to a single-mode fiber. Such an FPI exhibits an average RI sensitivity of 240dB/RIU over a wide RI range of 1.3326–1.4305, with a maximum sensitivity of 1110.7dB/RIU at the RI of 1.4305. In addition, the FPI can also achieve the simultaneous measurement of the RI and temperature.