Fiber-based vortex beam source operating in a broadband or tunable mode

We demonstrate a fiber-based optical vortex beam source operating in broadband or tunable mode in the spectral range of 1100-1400 nm. The vector vortices of the total angular momenta equal to +2, 0, and -2 are obtained by converting the respective linearly polarized (LP11) modes of the two-mode birefringent PANDA fiber with stress-applying elements by gradually twisting its output section. At the input end, the PANDA fiber is powered by broadband supercontinuum or tunable Raman solitons generated in the LP11 polarization modes of a birefringent microstructured fiber with a specially designed dispersion profile and coupled to the respective LP11 modes of the PANDA fiber. Two pulse lasers operating in different regimes (1 ns/1064 nm and 190 fs/1037 nm) were used as the pump to generate supercontinuum or tunable solitons directly in the LP11 modes of the microstructured fiber purely excited with a special Wollaston prism-based method. The high modal and polarization purities of the beams after successive transformations were experimentally confirmed. We also proved the vortex nature of the output beams using shearing interferometry. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement