Single-Mode Sapphire Fiber Temperature Sensor
Mohan Wang, Patrick S. Salter, F.P. Payne, Adrian Shipley, Igor N. Dyson, Tongyu Liu, Tao Wang, Kaihui Zhang, Jian Zhang, Zhitai Jia, Stephen Morris, Martin J. Booth, Julian Fells
Abstract
Sapphire fiber can withstand temperatures of around 2000 °C, but it is multimoded, giving poor precision sensors. We have demonstrated a single-mode sapphire fiber Bragg grating temperature sensor operating up to 1200 °C. A single-mode sapphire fiber was formed by writing a depressed cladding waveguide along the length of a 100-μm diameter sapphire fiber using a femtosecond laser. A second-order Bragg grating sensor was inscribed within the waveguide, achieving a reflectivity of >90% and a narrow bandwidth of <0.5 nm. The single-mode sapphire fiber was fusion spliced to standard silica single-mode fiber. The sensor was vibration-tested over a 10 Hz to 30 kHz range with 30 μm displacement, resulting in minimal Bragg wavelength variation of <30 pm standard deviation. The sensor was furnace-tested to 1200 °C, showing ±0.08% repeatability above 1000 °C. This demonstrates the high precision sensing capability of single-mode sapphire fiber Bragg grating sensors with end-to-end single mode interrogation.