Fig. 1. Characterization of the as-prepared few-layer Bi2Se3. (a) TEM image, (b) AFM image, (c) height profile diagram, and (d) measured saturable absorption curve at 1.56 μm wavelength.

Fig. 2. Experiment setup of the proposed narrow-linewidth single-frequency passively Q-switched EDFL. WDM, wavelength division multiplexer; EDF, erbium-doped fiber; PC, polarization controller; OC, optical coupler. Inset: transmission spectrum of the narrow-bandwidth FBG.

Fig. 3. MLM Q-switching characteristics. (a) Optical spectrum of the MLM Q-switched laser; (b) RF output spectrum of the MLM Q-switched laser in 100-MHz span (inset: 1-GHz span); (c) typical oscilloscope traces of the MLM Q-switched pulse trains; (d) single pulse envelope from the MLM Q-switched laser.

Fig. 4. SLM Q-switching characteristics. (a) Optical spectrum of the SLM Q-switched laser in a 30-nm span; (b) optical spectrum comparison of the SLM (red line) and the MLM (gray line) Q-switched lasers; (c) RF output spectrum comparison of the SLM (red solid line) and the MLM (gray dashed line) Q-switched lasers; (d) laser linewidth measurement with a resolution bandwidth (RBW) of 1 kHz by employing a self-heterodyne method; experimental data (red solid line), fitting (blue solid line), and equipment background (black dashed line).

Fig. 5. (a) Typical oscilloscope traces of the SLM Q-switched pulse trains; (b) evolution of the single-pulse envelope; (c) repetition-rate and pulse duration as a function of the incident pump power; (d) RF output spectrum (inset: broadband RF output spectrum); (e) output power versus pump power.