Polarization Controlled State-Switchable Mode-Locked Laser Based on Nonlinear Polarization Rotation

Mode-locked (ML) lasers based on nonlinear polarization rotation (NPR) can generate diverse pulses and spectral states depending on their polarization evolution processes. However, developing dynamically controllable polarization-dependent saturable absorber technology remains a significant challenge. Here, we demonstrate a state-switchable fiber laser system that employs a polarization-maintaining acoustically induced fiber grating (PM-AIFG) serving dual functions: as a saturable absorber for NPR mechanism and as an active control element for dynamic state manipulation. This system enables continuous, rapid switching between continuous-wave (CW) and ML states at a switching rate up to hundreds of hertz without pump power adjustment. Spectral bandwidth tuning is achieved through intracavity polarization environment modulation. The laser exhibits two distinct operational regimes: in the short-cavity configuration, it generates width-tunable dissipative soliton resonance (DSR) pulses (1.95-3.5 ns) at high power levels, while the long-cavity arrangement enhances nonlinear effects to produce stable Raman components and controllable multi-pulse bundles. This platform establishes a new paradigm for active laser state control through multidimensional parameter manipulation.