Multi-wavelength erbium-doped fiber laser with tunable orbital angular momentum beams output

We propose and experimentally demonstrate a multi-wavelength erbium-doped fiber laser (EDFL) with orbital angular momentum (OAM) mode output. Employing a Mach–Zehnder filter, a Sagnac loop filter, and a mode-selective coupler, the proposed EDFL achieves single-, dual-, triple- and quadruple-wavelength outputs of OAM modes. The tunable range of the output wavelengths is up to 22.64 nm. Besides, the multi-wavelength laser is able to emit OAM modes with its topological charge of $ \pm {1}$±1. The proposed EDFL has the advantages of wide wavelength tunability, good stability, high signal-to-noise ratio (higher than 34 dB), and high mode purity (up to 95%), which may be applied for mode-division-multiplexing optical communication and optical fiber sensing systems.