Sub-millisecond response fiber-optic temperature sensor based on microfabricated silicon Fabry-Pérot interferometer

• Novel silicon short-cavity FPI sensor achieves sub-millisecond response (0.54 ms). • MEMS fabrication enables miniaturization and faster thermal response. • Response time can be further optimized to 0.1 ms with current technology. • Wide-range testing (-40 °C to 120 °C) validated with a novel oil-bath system. This study proposes a novel fiber-optic temperature sensor based on a microfabricated short-cavity silicon Fabry-Pérot interferometer (FPI), achieving miniaturized sensing unit and sub-millisecond response. The sensor employs micro-electromechanical systems (MEMS) technology and fiber-waveguide coupling technology to fabricate a 17-μm-length and 125-μm-diameter silicon-based FPI on the fiber tip. By significantly reducing the cavity length of the FPI, the free spectral range (FSR) is markedly expanded, enabling temperature demodulation through intensity measurement while maintaining a broad monotonic measurement range. Experimental results show that the sensor has an FSR of 19.8 nm near 1550 nm with 20.0 dB modulation depth. The sensor exhibits monotonicity within a temperature range of 98 ℃ near normal temperature. For establishing the functional relationship between the reflectivity of the sensing head and the ambient temperature, the test data of temperature induced reflectivity variation of the sensor from −5 ℃ to 63 ℃, is fitted by a third-order polynomial. The agreement between the fitting results and experimental data demonstrates that the sensor can be calibrated for measurement within a temperature range of 68 ℃. The temperature stability of the fiber-optic sensor is 0.076 ℃, which means the resolution is better than 0.1 ℃. We also estimate that the average sensitivity of the sensor is approximately 66 mV/℃ under reasonable conditions. Immersion testing by dipping the sensing head quickly into hot water reveals a 0.54 ms response time, which is consistent with theoretical calculations. The standardized fabrication process of the sensor satisfies industrial production requirements. The developed compact, fast-responding fiber-optic temperature sensor demonstrates strong potential for oceanographic temperature monitoring.