Fig. 1. Experimental setup of an RFL.

Fig. 2. (a) The maximum power of the first-order Stokes light versus the length of the passive fiber. (b) The simulated results of the residual pump, first- and second-order Stokes light.

Fig. 3. (a) Experimental setup of a tunable RFL. (b) Detailed setup of the tunable pump source (AMP1, pre-amplifier; AMP2, main amplifier; PBS, polarization beam splitter; OTF, optical tunable filter; GDF, germanium-doped fiber; ISO, isolator). (c) Experimental setup for PER measurement.

Fig. 4. (a) Maximum output power and corresponding linewidth of the pump source. (b) The spectra of the pump source.

Fig. 5. (a) Spectra of the RFL. (b) Power and corresponding linewidth of the first-order Stokes light at different wavelengths.

Fig. 6. (a) Output power evolution of the random laser and (b) the output spectra of the RFL. (c) The spectra and (d) the linewidth evolution of the first-order Stokes light.

Fig. 7. (a) PER of the pump source and the corresponding first-order Stokes light at the maximum output power. (b) The PER evolution of the pump power and corresponding first-order Stokes light at the pump wavelength of 1067.5 nm.

Fig. 8. Radio frequency of the random laser at 1124.72 nm. Inset: the temporal trace of the laser output.

Fig. 9. Comparison between simulation results and experimental results.