We present an optical scheme to encode and decode $2\mathrm{bits}$ of information into different orbital angular momentum (OAM) states of a paraxial optical beam. Our device generates the four light angular momentum states of order $\pm 2$ and $\pm 4$ by spin-to-orbital angular momentum conversion in a triangular optical loop arrangement. The switching among the four OAM states is obtained by changing the polarization state of the circulating beam by two quarter-wave plates, and the $2\mathrm{bit}$ information is transferred to the beam OAM exploiting a single q plate. The polarization of the exit beam is left free for an additional $1\mathrm{bit}$ of information. The switching among the different OAM states can be as fast as a few nanoseconds, if suitable electro-optical cells are used. This may be particularly useful in communication systems based on light OAM.