Delivering Transverse-Mode Switching Based on All-Fiber Femtosecond Laser

Fiber lasers operating in on-demand spatial transverse modes have recently gained extensive attention due to their great flexibility in practical applications. Typically, free-form mode converters are widely used to generate flexible transverse modes in solid-state or fiber lasers, which call for a strict calibration and are susceptible to mechanical perturbations [1]. Recently, fiber-based few-mode fiber Bragg grating (FMF-FBG) has been developed and applied to transverse-mode switchable mode-locked all-fiber lasers [2]. However, FMF-FBG usually has a narrow-band mode conversion resulting in picoseconds pulse duration. Moreover, most FMF-FBG based fiber lasers operate at the lowest transverse modes (LP
₀₁
and LP
₁₁
modes).