  Moving metasurfaces support guided waves exhibiting unusual optical
properties, including strong anisotropy, nonreciprocity, and hyperbolic
dispersion. However, for these phenomena to be noticeable, high speeds are
typically required, challenging their practical implementation. Here, we show a
viable route towards the realization of one-way hyperbolic propagation in
metasurfaces placed synthetically in motion through traveling-wave space-time
modulation. In addition to non-reciprocal hyperbolic propagation, the proposed
time-modulation scheme induces additional exotic opportunities for nanophotonic
systems, such as efficient nonreciprocal frequency conversion and mode
transfer.
