Vortex beams with zero orbital angular momentum and non-zero topological charge

We study the field structure of the vortex beam generated via coherent fiber-array where beamlets are arranged along a circle. Each beamlet is an aperture-bounded Gaussian beam emerging from fiber output with constant phase. The phase shift between neighbor beamlets is the same, and the total phase incursion along the circle is equal to 2πl (l is integer). The total orbital angular momentum of the beam is equal to zero for any propagation distance and arbitrary l. We show that the central part of the far field corresponds to an optical vortex with the orbital angular momentum and the topological charge equal to l (l < N/3, N is the number of beamlets). The dependencies of the orbital angular momentum of the vortex beam on the receiving aperture size and the propagation distance are analyzed.