Fig. 1. Schematic of the experimental setup for the WT-RFL. OC, optical coupler.

Fig. 2. Numerical simulation spectra of the RBGA and π-FBG. (a) Reflection spectrum of the RBGA. (b) Transmission spectrum of the π-FBG. (c) Random lasing modes with multiple gain. (d) Simulation lasing spectra of the WT-RFL.

Fig. 3. Reflection spectra and transmission spectra of (a) RBGA1 and (b) RBGA2.

Fig. 4. (a) Reflection and transmission spectra of two RBGAs and π-FBG. (b) The wavelength of π-FBG as a function of the strain.

Fig. 5. Output power versus different pump power.

Fig. 6. Output spectra measured under different pump power at 1537.452 nm.

Fig. 7. Laser spectra at different measured wavelengths.

Fig. 8. Wavelength and peak-power fluctuations of selected wavelengths versus time.