Direct Emission of Two-Color Vortex Beams at 1.0 μm and 1.5 μm Wavebands From an All-Fiber Laser

In this letter, we demonstrated an all-fiber laser that can simultaneously radiate dual-color vortex beams by incorporating a dual-channel mode-selective coupler (DC-MSC) into the laser cavity. By optimizing the phase-matching condition between LP01 and LP11 modes, wavelength-dependent mode coupling could be observed. In this case, a broadband mode conversion with two isolated bands can be achieved, which totally covers the gain bands of ytterbium and erbium ion, enabling the simultaneous generation of vortex beams (VBs) at $1.06~\mu \text{m}$ and $1.55~\mu \text{m}$ wavebands. With intra-cavity mode conversion and polarization controlling, a coaxial two-color VB is transmitted directly from the laser cavity, providing a more compact dual-beam light source for subsequent vortex nonlinear frequency conversions, such as wavelength extension to the red light and the mid-infrared ( $3~\mu \text{m}$ ) wavebands.