Femtosecond Laser-Inscribed Excessively Tilted Fiber Grating Sensor With CFBG for Simultaneous Measurement of Refractive Index and Temperature

A novel optical fiber grating sensor fabricated using femtosecond laser direct writing technology, integrating 45° and 81° tilted fiber gratings (TFGs), a chirped fiber Bragg grating (CFBG), and a fiber Bragg grating (FBG), is proposed for simultaneously measuring temperature and refractive index (RI). The 81°-TFG serves as a high-sensitivity, easily identifiable RI sensing unit, while the 45°-TFG functions as a polarizer, forming an all-fiber structure. By inscribing the CFBG after the TFG, the sensor can measure the reflection spectrum of the TFG, enabling a probe-type design. The FBG decouples temperature measurements, thereby addressing temperature crosstalk problems. Experimental results demonstrate that within the RI range of 1.333–1.375, the sensor achieves a sensitivity of 516.83 nm/RIU. For temperature measurements within the range of 20 °C–100 °C, the average temperature sensitivity is 11.39 pm/°C. The sensor has the advantages of simple manufacturing, a compact and stable structure, and easy identification, making it more conducive to practical applications.