In-Line Fabry–Perot Etalons Based on Hollow-CorePhotonic Bandgap Fibers for High-Temperature Applications

In this paper, we report a novel in-line fiber Fabry-Perot (F-P) etalon, consisting of a section of hollow-core photonic bandgap fiber (HC-PBGF) spliced between two single mode fibers. The fabrication process of such a sensor is simple and straightforward, including only cleaving and splicing. The sensing characteristics of the F-P etalon based on HC-PBGF, including high temperature, strain, bend, and transverse load, are fully investigated by experiments, for the first time to our knowledge. It is found that such a F-P etalon can be used under high temperatures of up to 600??C, and has a low cavity-length-to-temperature sensitivity of ~ 1.4 nm/??C, while it has a relatively high strain sensitivity of ~ 5.9 nm/????. Moreover, this F-P etalon is insensitive to bend or transverse load. Furthermore, the long cavity length (> 1 cm) of the sensor makes it suitable for multiplexing. These characteristics would make this HC-PBGF-based F-P etalon to be an excellent strain sensor or gas sensor for use in high-temperature environments.