Polarization‐Dependent Radiative Loss Engineering for Unidirectional Reflection in Terahertz Metasurfaces

Abstract Direction‐dependent control of propagating electromagnetic radiation plays a crucial role in emerging photonic technologies, including isolators, circulators, detectors, and sensors. Typically, the directional control is achieved through nonreciprocal mechanisms involving magnetic biasing, spatiotemporal modulation, or nonlinear effects. However, incorporation of these techniques into the terahertz (THz) regime is cumbersome due to the material limitations and integration complexity. In this context, a planar metasurface design composed of geometrically asymmetric split ring resonators (SRRs) is presented, enabling unidirectional reflection. The asymmetry is induced by laterally displacing the capacitive gap in SRRs. The geometrical asymmetry in SRR induces asymmetric radiative loss, resulting in strong reflection from one direction and near‐complete suppression from the opposite. This thorough investigations demonstrate a reduction in resonance intensity (and resonance Q‐factor) with increasing geometric asymmetry, indicating redistribution of energy stemming from radiative loss engineering. The demonstrated metasurface designs enable controlled unidirectional reflection by accessing dark modes through introducing asymmetry in well accepted SRR‐based planar metasurface configuration.