Figure 3.

A schematic diagram of experimental setup of three-fold cyclic transformation of OAM modes. There are OAM beam splitters (OAM BSs) which consist of a Mach-Zehnder interferometer with Dove prisms. $\alpha /2$ means relative angle between the two Dove prisms. The first OAM BS ($\alpha =\pi$) and the final OAM BS ($\alpha =-\pi$) change a direction of propagation of a photon whose OAM value is odd and even, respectively. The second OAM BS ($\alpha =\pi /2$) separates a photon whose OAM value is 0 and 2. With OAM holograms, the three-fold cyclic transformation of OAM modes $\{-1,0,1\}$ is accomplished.