Switchable multi-wavelength actively Q-switched random fiber laser based on an NPR-assisted Lyot filter and a nested fiber ring

In this paper, a compact and switchable multi-wavelength actively Q-switched random fiber laser (RFL) is experimentally demonstrated through the strategic integration of a nested fiber ring (NFR) and a nonlinear polarization rotation (NPR)-assisted Lyot filter. The NFR enables a significant enhancement of random distributed feedback with a meter-scale fiber length, while the NPR-assisted Lyot filter provides a dynamically comb-filtering function. Compared with conventional RFLs that typically operate in continuous-wave (CW) regime with fixed lasing wavelengths, this hybrid architecture introduces both agile wavelength switching and stable pulsed operation. Experimental results reveal that the pulse evolution and splitting behavior are critically governed by the modulation waveform (sine, square, and ramp), with a maximum of seven pulses per cycle achieved under a ramp wave. Moreover, by adjusting the intracavity polarization state, the laser output can be switched from single to six wavelengths, and the wavelength spacing in multi-wavelength states is fine adjustable. The laser source has rich dynamics and controllable temporal and spectral properties, which has potential applications in optical sensing and multi-channel communications.