Broadband Janus Scattering from Tilted Dipolar Metagratings

Abstract Electromagnetic resonances in meta‐atoms have empowered optical interfaces with unprecedented abilities in wavefront manipulation. Despite the versatile applications, energy efficiency and bandwidth improvement are still theoretically constrained by the dispersion feature of resonances in mesoscopic structures. Here, a nontrivial phase modulation mechanism is exposed that breaks the efficiency and bandwidth limit in electric dipolar resonances. By arranging electric dipoles into tilted periodic arrays, the time‐reversed scattering channels are suppressed and dispersionless reflection as well as controllable phase retardation from planar interfaces are achieved. Two types of reflectionless metagratings are demonstrated to support the theoretical prediction. Janus phase retarders show asymmetric phase modulation over a broad spectrum protected by reciprocity. Janus backscattering mirrors retroreflect incident waves for one side while showing transparency in the time‐reversed reflection channel. Experimental measurements validate the concept of broadband Janus scattering at optical axes misalignment interfaces.