An experimental scheme for one-way, shape-preserving control of a light beam. A honeycomb moire photonic lattice is optically written into a three-level rubidium vapor under electromagnetically induced transparency; its flat bands and unequal site potentials localize a forward-propagating probe beam, while for a counter-propagating probe the Doppler shift from thermal atomic motion breaks the EIT resonance so the beam disperses. The result is nonreciprocity in both transverse beam profile and transmitted intensity (isolation about 20.1 dB), using the Doppler effect as the symmetry-breaking resource.
Magnetic-free nonreciprocal optical devices let light pass one way but not the other, which is essential for integrated photonic signal processing; most existing schemes, however, distort the beam's …