1：Experimental Design and Method Selection:

The study involves preparing a saturable absorber (SA) device by depositing GO-COOH nanosheets aqueous solution on a D-shaped fiber. The nonlinear saturable absorption property of the SA is measured using a home-made femtosecond laser.

2：Sample Selection and Data Sources:

GO-COOH solution is prepared by liquid phase exfoliation method. The D-shaped fiber is fabricated by grinding a single-mode fiber.

3：List of Experimental Equipment and Materials:

- Laser diode (LD) with emission centered at 975 nm

4：Experimental Procedures and Operational Workflow:

The mode-locked laser is achieved by inserting the SA into the erbium-doped fiber (EDF) laser setup. The performance of the laser is monitored using various optical and electronic instruments.

5：Data Analysis Methods:

The nonlinear saturable absorption property is fitted by a specific function to determine modulation depth and saturable intensity. The laser's output characteristics are analyzed using the instruments mentioned.