A Miniaturized Optical Fiber Tip High-Temperature Sensor Based on Concave-Shaped Fabry–Perot Cavity

We present a miniaturized optical fiber tip Fabry–Perot interferometer for high-temperature measurement based on a concave-shaped cavity. The fabrication process of the diaphragm-free Fabry–Perot cavity is quite simple, involving only two steps: fusion splicing and cleaving. By adjusting the arc power during fusion splicing, a concave-shaped structure is obtained, through which the light is coupled/split into the wall of the spliced hollow core fiber. By cleaving the end-face of the hollow-core fiber, a concave-shaped diaphragm-free Fabry–Perot interferometer is formed. The temperature response of the sensor was demonstrated, showing a high-temperature tolerance up to 1000 °C and a sensitivity of 0.01226 nm/°C. The proposed sensor, with all-silica-structure, high compactness, robustness, and ease of fabrication, could find wide applications in high-temperature harsh environments.