Fig. 1. Morphological characteristics of WTe₂ saturable absorber. (a) SEM image for micro-nanofiber side coated with WTe₂ film; (b) SEM image of the cross section of micro-nanofiber; optical microscope images of the waist region of sample (c) without and (d) with 650 nm guiding red light

Fig. 2. Nonlinear characteristics of WTe₂ saturable absorber. (a) Saturable absorption property; (b) relaxation time

Fig. 3. Schematic of passively mode-locked erbium-doped fiber laser

Fig. 4. Mode-locking pulse output characteristics for erbium-doped fiber laser. (a) Relationship between pump power and laser output power; (b) optical spectrum with the bandwidth of 11.54 nm; (c) radio frequency spectrum at fundamental frequency of 26.6 MHz with 10 Hz resolution, and the inset shows radio frequency spectrum of 1 GHz bandwidth; (d) autocorrelation curves for output pulse with a pulse duration of 231 fs with sech2· fitting