  In hyperbolic 2D materials, energy is channeled to their deep subwavelength
polaritonic modes via four narrow beams. Here we consider the launching of
surface polaritons in the hyperbolic 2D materials and demonstrate that
efficient uni-directional excitation is possible with an elliptically polarized
electric dipole, with the optimal choice of dipole ellipticity depending on the
materials optical constants. The selection rules afforded by the choice of
dipole polarization allow turning off up to two beams, and even three if the
dipole is placed close to an edge. This makes the dipole a directionally
switchable beacon for the launching of sub-difractional polaritonic beams, a
potential logical gate. We develop an analytical approximation of the
excitation process which describes the results of the numerical simulations
well and affords a simple physical interpretation.
