Micro Multicavity Fabry–Pérot Interferometers Sensor in SMFs Machined by Femtosecond Laser

We propose and demonstrate a compact micromulticavity Fabry–Pérot (FP) optical fiber tip sensor for refractive-index (RI) and temperature measurement, which is fabricated by laser micromachining. The fabrication process of the sensor offers a quite simple way to fabricate compact in-line FP at a low cost. At the end of the single-mode fiber, there is a short air FP cavity, which forms a multicavity together with the fiber flat face tip. Two independent cavities exist in our sensor, and the air cavity is used for RI sensing and the glass cavity for temperature sensing, thus, avoiding the temperature and RI cross-sensitivity. The measurement results show that the in-line FPI exhibits an RI sensitivity of 1074.36 nm/RIU and a temperature sensitivity of 10.6 ${\rm \pm}/^{\circ}{\rm C}$ .