1：Experimental Design and Method Selection:

The experiment is based on a Sagnac interferometer with a low modal crosstalk mode MUX/DEMUX to achieve spatial-mode switching and multi-wavelength tuning.

2：Sample Selection and Data Sources:

The main fiber ring cavity includes a 980 nm laser diode, a 980/1550 nm wavelength division multiplexer, a 5 m single mode EDF, an optical isolator, a PC2, two 1 × 4 single-mode optical couplers, a 4 × 1 optical switch, mode MUX1/DEMUX1, and a 90:10 few-mode optical coupler.

3：List of Experimental Equipment and Materials:

980 nm laser diode, 980/1550 nm wavelength division multiplexer, 5 m single mode EDF, optical isolator, PC2, 1 × 4 single-mode optical couplers, 4 × 1 optical switch, mode MUX1/DEMUX1, 90:10 few-mode optical coupler, Sagnac interferometer components.

4：Experimental Procedures and Operational Workflow:

The setup involves generating higher-order modes via mode MUX/DEMUX, adjusting the polarization controller for multi-wavelength lasing, and monitoring output via optical spectrum analyzer and CCD camera.

5：Data Analysis Methods:

The spectra properties and stabilities are measured by an optical spectrum analyzer, output power by a power meter, and mode profiles by a CCD camera.