1：Experimental Design and Method Selection:

The sensor cascades an intrinsic Fabry–Perot interferometer (IFPI) and an extrinsic Fabry–Perot interferometer (EFPI) for temperature and pressure sensing, respectively. The pressure sensor is based on a diaphragm-free structure. Two optical path differences are interrogated simultaneously by using the fast Fourier transform-based white-light interferometry and the peak-to-peak method.

2：Sample Selection and Data Sources:

The sensor was fabricated using single mode fiber (SMF), hollow core fiber (HCF), and coreless fiber (CF). A micro air hole was fabricated at the center of the end face of the lead-in SMF 1 using a femtosecond laser.

3：List of Experimental Equipment and Materials:

A broadband light source (BBS), a pressure meter, a muffle furnace, and a home-made demodulator were used. The fs laser was employed to drill a micro-channel at the side wall of the HCF.

4：Experimental Procedures and Operational Workflow:

The sensor was sealed in a gas chamber and placed in the center of the muffle furnace. The temperature was increased from 40 °C to 1100 °C with a step of ~100 °C. At each step, the pressure was increased from 0 to 10 MPa with a step of 1 MPa.

5：Data Analysis Methods:

The reflected spectrum was processed by the FFT. Two band-pass filters were used to filter out main frequency components of the EFPI and the IFPI. Interference spectra were reconstructed by using the inverse fast Fourier transform (IFFT).