Fig. 1. (a) TEM image of the GNRs (Inset: aqueous solution of GNRs). (b) Histogram of the aspect ratio distribution.

Fig. 2. (a) Photograph of the filmy GNR SA (Inset: photograph of the fiber end attached to the GNR SA). (b) Nonlinear saturable absorption curve of the prepared GNR SA.

Fig. 3. Experimental setup of Q-switched EDF ring laser.

Fig. 4. Q-switched operation at a pump power of 56.4 mW. (a) Q-switched pulse train (Inset: the single zoomed-in pulse). (b) The corresponding optical spectrum.

Fig. 5. (a) Q-switched pulse trains with different repetition rates. (b) Pulse duration and repetition rate versus pump power.

Fig. 6. (a) Spectra of the wavelength-tunable, Q-switched operation at a pump power of 202.2 mW. (b) Typical Q-switched pulses centered at 1558.22 nm. (c) Pulse repetition rate and output power versus tunable wavelength. (d) Pulse width and energy versus tunable wavelength.

Fig. 7. (a) Various QML pulse trains under different pump powers. (b) Magnified view of the single QML pulse. (c) The corresponding optical spectrum. (d) The corresponding radio frequency spectrum.