1：Experimental Design and Method Selection:

The study involves developing a Lorentzian demodulation algorithm for FBGs in multimode optical fibers. The method includes measuring the FBG-reflected spectrum, subtracting the spectral noise floor, and fitting the spectrum with a Lorentzian curve to derive the Bragg wavelength.

2：Sample Selection and Data Sources:

A 2-mm-long FBG was inscribed in a 1.4-m-long perfluorinated graded-index (PFGI) polymer optical fiber (POF). The POF has a three-layered structure and was used for strain sensing.

3：4-m-long perfluorinated graded-index (PFGI) polymer optical fiber (POF). The POF has a three-layered structure and was used for strain sensing. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: The setup included an amplified spontaneous emission (ASE) source, an optical circulator, and an optical spectrum analyzer (OSA, AQ6370, Yokogawa). The FBG was inscribed using a femtosecond laser system (High Q femtoREGEN).

4：Experimental Procedures and Operational Workflow:

The output from the ASE source was injected into the PFGI-POF, and the reflected light from the FBG was guided to the OSA. A section of the PFGI-POF including the FBG was strained using automatic translation stages.

5：Data Analysis Methods:

The Bragg wavelength was detected using the Lorentzian demodulation algorithm, and its performance was compared with the maximum and centroid detection methods.