Hybrid structured fiber-optic Fabry–Perot interferometer for simultaneous measurement of strain and temperature

We fabricate and experimentally demonstrate a hybrid structured Fabry–Perot interferometer (FPI) embedded in the middle of a fiber line for simultaneous measurement of axial strain and temperature. The FPI is composed of a silica-cavity cascaded to a spheroidal air-cavity, both of which are formed in a hollow annular core fiber (HACF). The fabrication process of the FPI includes only a fusion splice between a single-mode fiber and a HACF and several electrical arc discharges at the HACF near the splice point. Experimental results show that the strain and temperature sensitivities of the air-cavity can be 5.2 pm/μe and 1.3 pm/C°, respectively, and those of the silica-cavity can be 1.1 pm/μe and 13 pm/C°, respectively. The different sensitivities of silica-cavity and air-cavity to strain and temperature enable us to implement simultaneous sensing in strain and temperature.