Taming Light: One-Way Optical Signals Without Distortion

Optical information processing relies on devices that allow light to travel in one direction while blocking it from returning—a property known as nonreciprocity. However, achieving this without heavy magnets typically relies on optical dispersive effects. Unfortunately, these effects often cause the light beam to spread out or break into pieces, making the signal difficult to match with subsequent components.

In a significant step forward, researchers have experimentally demonstrated the 'nonreciprocal transverse localisation' of light using a moiré photonic lattice in atomic vapours. A moiré lattice is a complex interference pattern created by overlapping grids. By utilising a honeycomb moiré profile for the coupling field, the team observed that the output pattern changes drastically depending on the direction of propagation.

Driven by atomic thermal motion, the light beam remains tight and localised when moving in the forward direction. Conversely, when travelling in reverse, the beam becomes dispersive, spreading out in both size and intensity. This novel approach offers a way to prevent backscattering while maintaining a controlled beam profile, ensuring high-quality transmission for functional optical devices.