Tunnel vortex selection in optical coupler

In spite of the fact that optical vortices are eigen modes of the ideal optical fiber and are well studied, the fiber excitation and vortex propagation processes by no means represent the last problem of fiber singular optics. Initiators of such situation come forward two physical processes. The first of them is associated with the cutoff conditions for the eigen modes. The fact is that the same cutoff frequency corresponds to at once three eigen waves: CV, TE and TM modes