Stable and selectable generation of LP/CVB/OAM modes in an all-fiber ring laser via a low modal-crosstalk mode multiplexer/demultiplexer

A universal scheme for stable and selectable LP, CVB, and OAM beam generation in an all-fiber ring laser is proposed and experimentally demonstrated. Lasing in a specific or arbitrary combination of multiple transverse modes is achieved by integrating a low modal-crosstalk mode multiplexer/demultiplexer (MUX/DEMUX) and a simple N × 1 optical switch into the laser cavity. The LP modes are generated using a mode MUX composed of cascaded mode-selective couplers, fabricated by tapering a designed weakly coupled six-mode double-ring-core fiber and a single-mode fiber. By leveraging the conversion relations among LP, CVB, and OAM modes, CVB/OAM outputs are obtained through precise control of polarization states and LP mode combinations. The mode intensity profiles, slope efficiencies, optical spectra, and stabilities of the generated LP/CVB/OAM lasing beams are investigated. Experimental results show that the proposed universal and compact all-fiber laser has promising applications in optical communication systems, high-resolution imaging, particle trapping, high-dimensional quantum entanglement, and material processing.