Nonreciprocal Polychromatic Radiation from a Space-Time-Modulated Omega-Topology Meta-Transceiver

Abstract

Time-modulated metasurfaces offer a magnet-free route to nonreciprocal wave control, but existing realizations modulate only the electric response of the structure, and proposals for simultaneous electric-magnetic modulation have so far remained theoretical. We experimentally demonstrate a space-time-periodic meta-transceiver whose omega-topology unit cell integrates varactor-loaded electric (dipole) and magnetic (ring) resonators, both modulated by a common unidirectional traveling-wave bias. This modulation gives rise to two independent, experimentally resolved manifestations of nonreciprocity: on transmit, the incident field is efficiently converted into a polychromatic comb of harmonics that radiate at distinct, bias-reconfigurable angles, while on receive, the same modulation instead suppresses frequency conversion and routes the incoming wave preferentially toward one port over the other. These two effects - nonreciprocal polychromatic conversion and unidirectional wave routing - arise from a single unidirectional space-time modulation but act on distinct physical observables, frequency content and spatial direction, respectively. Measured near the electric resonance with a shared bias, these effects characterize the complete cell and do not separate its electric and magnetic contributions. Our results establish the space-time-modulated omega-topology cell as an experimentally viable platform for reconfigurable, full-duplex nonreciprocal wave transformation.