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.