All-SiC fiber-optic sensor for pressure and temperature dual-mode sensing in harsh environments

This paper presents a fiber-optic Fabry–Perot (FP) sensor with an all-silicon carbide (SiC) structure for pressure and temperature dual-mode sensing in harsh environments. The all-SiC sensing diaphragm and vacuum FP cavity were formed by direct bonding of a 6H-SiC (N-doped) diaphragm with a 6H-SiC (V-doped) substrate. The variation in length of the FP cavity was used to measure the external pressure, while the principle of temperature sensing was due to the temperature dependence of the refractive index and thermal expansion of the SiC substrate. The pressure and temperature characteristics of the sensor were calibrated from 25 °C up to 700 °C over a pressure range of 0–1.0 MPa. The pressure sensor achieved high sensitivity (174.3 nm/MPa) and linearity (R2 = 0.999 at 700 °C), the spectral sensitivity of the temperature sensing being approximately 32.12 pm/°C. Moreover, the temperature-pressure cross-sensitivity was as little as 4.98 °C/MPa. The dual-mode sensing capability of the all-SiC fiber-optic sensor demonstrated great promise for applications in extremely high-temperature environments.