Fig. 1. (a) Linear absorption of the graphene solution (alcohol contribution subtracted); (b) GSA film optically deposited on fiber tip; (c) Raman spectrum of GSA film on fiber tip; (d) nonlinear transmittance at the laser operating wavelength.

Fig. 2. All-fiber laser schematic. LD, laser diode; WDM, wavelength-division multiplexer; EDF, Er-doped fiber; PI-ISO, polarization-insensitive isolator; PC, polarization controller; GSA, graphene saturable absorber; OC, optical coupler.

Fig. 3. Fundamental mode-locking experimental results. (a) Optical spectrum; (b) temporal waveform; (c) pulse profile; (d) RF spectrum with 10 Hz resolution (inset, 1000 MHz span).

Fig. 4. BS experimental results. (a), (b), and (c) BS spectral modulations as functions of intracavity polarization, with a stable CW-free spectrum shown in (c) (inset, spectral magnification around the central wavelength, 1558 nm); (d) autocorrelation trace of the pulses (inset, pulse profile). The pulse separation Δτ modulates the spectrum with a period of 1/Δτ. (e) Temporal waveform of the intracavity circulating pulses; (f) RF spectrum with 10 Hz resolution (inset, 500 MHz span).

Fig. 5. HML experimental results. (a) Optical spectrum (inset, pulse profile); (b) temporal waveform; (c) RF spectrum with 20 kHz resolution (inset, 1500 MHz span); (d) output power and harmonic order as functions of pump power.