Fig. 1. Optical images of (a) bare microfiber and (b) microfiber coated with BP flakes, (c) experimental setup of the balanced twin-detector measurement device, (d) the measured saturable absorption and its corresponding fitting curve.

Fig. 2. Schematic of the BP-based Q-switched fiber ring laser. LD, laser diode; WDM, wavelength division multiplexer; OC, optical coupler; EDF, Er-doped fiber; FBG, fiber Bragg grating; PC, polarization controller.

Fig. 3. Dual-wavelength Q-switched operation when the pump power is 95 mW. (a) Output optical spectrum of the dual-wavelength Q-switched fiber laser, (b) typical Q-switched pulse train, (c) single pulse envelope, (d) the RF spectrum.

Fig. 4. (a) Average output power and pulse energy versus pump power, (b) the pulse repetition rate and duration versus pump power.

Fig. 5. Output spectra of dual-wavelength Q-switched operation taken at a 10 min interval over 1 h.

Fig. 6. Q-switched operation at a wavelength of 1542.4 nm filtered from dual-wavelength output. (a) Output optical spectrum, (b) typical Q-switched pulse train, (c) single pulse envelope, (d) the RF spectrum.

Fig. 7. Q-switched operation at a wavelength of 1543.2 nm filtered from dual-wavelength output. (a) Output optical spectrum, (b) typical Q-switched pulse train, (c) single pulse envelope, (d) the RF spectrum.

Fig. 8. Dual-wavelength Q-switched operation. (a) The average output power, (b) pulse energy, (c) pulse duration, and (d) repetition rate at the wavelengths 1542.4 nm and 1543.2 nm versus pump power.

Fig. 9. Q-switched operation at a single wavelength of 1542.4 nm. (a) Output optical spectrum, (b) typical Q-switched pulse train, (c) single pulse envelope, (d) the RF spectrum.

Fig. 10. Q-switched operation at a single wavelength of 1543.2 nm. (a) Output optical spectrum, (b) typical Q-switched pulse train, (c) single pulse envelope, (d) the RF spectrum.

Fig. 11. Single-wavelength Q-switched operation. (a) The average output power, (b) pulse energy, (c) pulse duration, and (d) repetition rate at the wavelengths 1542.4 nm and 1543.2 nm versus pump power.