Multi-wavelength Q-switched random fiber laser based on stimulated Brillouin scattering and multimodal interference

We demonstrate a multi-wavelength Q-switched random fiber laser with the erbium-doped fiber as the gain medium and the Rayleigh scattering as the randomly distributed feedback in a 6 km long single-mode fiber. Q-switched pulses and sub-pulses with different repetition frequencies were generated with the pump power as 182 mW by combining the random cavity resonances and the Q-value modulation effect induced by the stimulated Brillouin scattering and nonlinear multimode interference in the graded-index multimode fiber. The pulse repetition rate increased continuously from 79 kHz to 113 kHz, and the corresponding pulse width exponentially decreased with the continuously increasing pump power, and a shortest pulse width of 1.85 μs was obtained. At the same time, a multi-wavelength spectrum with the equally spaced interval and an optical signal-to-noise ratio of ~31 dB was achieved. This laser has the unique properties different from the conventional resonant cavity lasers, which makes it a very promising light source in optical communication, imaging, and sensing applications.