Anomalous light steering by phase gradient metasurface with subwavelength metallic grating

Both sub-wavelength periodic structures and phase gradient metasurfaces have opened up new degrees of freedom to steer light in a compact structure, respectively. In this work, a metallic grating with a sub-wavelength period is introduced into the metasurface to modulate the light as the phase gradient beyond the critical value that propagation waves should be converted into surface waves. Both anomalous refraction and reflection beam steering can be observed in different frequency ranges. We comprehensively analyze the joint effect of the phase gradient and the sub-wavelength grating constraints. A local multiple reflection mechanism to amplify the phase gradient is proposed to reveal the underlying physics and the broadband manipulation performances, showing an excellent agreement. This work reveals richer physics and a more flexible manipulation mechanism for beam steering by combining phase gradient modulation and sub-wavelength periodic grating modulation. (paper)