1：Experimental Design and Method Selection:

The laser was fabricated from a nonlinear loop mirror (NOLM) and a coupler composed of a single mode fiber and few-mode fiber fused together. The NOLM is responsible for generating pulses, and the coupler acts as a beam splitter and mode converter.

2：Sample Selection and Data Sources:

A heavily erbium-doped fiber of

3：65 m was pumped with a 980 nm laser diode. List of Experimental Equipment and Materials:

Wavelength division multiplexing coupler (WDM), single-mode fiber (SMF), nonlinear loop mirror (NOLM), few-mode fiber (FMF), erbium-doped fiber (EDF), optical coupler (OC), polarization controller (PC1-3), polarization-independent isolator (ISO), charge coupled device (infrared camera, CCD).

4：Experimental Procedures and Operational Workflow:

The laser was operated continuously for 5 h, and the spectrum, repetition frequency, pulse width, and mode field pattern were measured.

5：Data Analysis Methods:

The optical spectrum and pulse width were measured using an optical spectrometer and an autocorrelator, respectively.