Femtosecond laser fabricated in-line micro multicavity fiber FP interferometers sensor

A compact micro multicavity Fabry-Perot (FP) optical fiber tip sensor is presented. In the end of the single-mode fiber (SMF), we drill a short air hole with femtosecond laser, which forms a multicavity together with the fiber flat face tip. The sensor has been experimentally tested for refractive index (RI) and temperature sensing by monitoring its wavelength shift. Simultaneous measurement of both changes in the ambient temperature and the RI can be realized using the sensitivity matrix. Measurement results show that the in-line FP exhibits the gas RI sensitivity of 867.76 nm/RIU and the temperature sensitivity of 7.8 pm/°C within the range of 24-104 °C, and the device is highly stable over time.