Switchable High-Order Transverse Mode Fiber Laser with over Ten Distinct Modes

High-order transverse modes (HOMs) possess unique spatial characteristics that have found applications in various fields such as high-precision optical measurements, optical manipulation, and laser processing. The order of the transverse modes plays a crucial role in determining the system performance. Current fiber laser output, however, remains predominantly constrained to low-order transverse modes due to the challenge of efficiently coupling the fundamental mode to higher-order transverse modes in existing fiber-type mode converters. Here, we propose a HOM fiber laser based on a tilted multimode fiber Bragg grating (TMM-FBG) that achieves switchable emission of 12 distinct linearly polarized (LP lm ) modes. In addition, 21 distinct orbital angular momentum (OAM ± l,m ) modes, featuring topological charges of l = 0, ±1, ±2, ±3, ±4, and ±5 and radial indices of m = 1, 2, and 3, can be obtained by adjusting polarization controllers within the resonator. The mode conversion from the fundamental mode to different HOMs is achieved by utilizing a TMM-FBG. Based on the mode-wavelength dependence of the fiber Bragg grating, the laser output can be easily switched among more than ten HOMs by tuning the resonant wavelength.