Observation of nonreciprocal transverse localization of light

Magnetic-free nonreciprocal optical devices that prevent backscattering of signals are essential for optical information processing. The achieved nonreciprocal behaviors mostly rely on various optical dispersive effects, leading to dispersive modulations of the spatial beam profiles, such as broadening and discretization, of incident signals. Such deformation inevitably reduces the matching with subsequent functional components. Here, we experimentally demonstrate the nonreciprocal transverse localization of light in a moiré photonic lattice in atomic vapors. When the probe field co- or counter-propagates with the forward coupling field with a honeycomb moiré profile, the output pattern can exhibit localized or dispersive behavior. The nonreciprocal behaviors (in both beam size and transmitted intensity) are from the atomic thermal motion. A backward Gaussian coupling field is also introduced to modulate the size and intensity of the backward probe, which experiences dispersive propagation. The current work provides an approach to control the transverse beam profile in nonreciprocal transmission.