All-Fiber Method for Real-Time Transverse-Mode Switching of Ultrashort Pulse

We demonstrate a real-time transverse-mode switching of ultrafast pulse via a cascading mode conversion. The cascading all-fiber mode converter is comprised of a mode-selective coupler (MSC) and an acoustically induced fiber grating (AIFG), which functions as a broadband and controllable beam shaper, and offers a real-time mode switching between LP11 and LP21 modes with $\sim ~190~\mu \text{s}$ switching time. Such a transverse mode-switchable all-fiber laser presents a pulse duration of 1.4 ps and flexible transverse-mode switching. We believe that this compact and robust all-fiber laser source would find promising applications in the field of ultrafast optics and structured light microscope.