Extension of Babinet’s relations to reflective metasurfaces: Application to the simultaneous control of wavefront and polarization

We extend Babinet's relations, which were originally derived for transmissive metasurfaces, to reflective metasurfaces embedding planar metallic structures in a substrate containing a mirror. To verify the extended Babinet's relations, we investigate two types of reflective metasurface embedding self-complementary structures, which produce a $\ensuremath{\pi}$ phase difference between two orthogonal linear polarizations under specific conditions required for the extended Babinet's relations. Both theoretical and experimental studies demonstrate a metasurface-based half-wave plate with a reflective metasurface including single self-complementary structures in the terahertz regions. In addition, we study a reflective metasurface with embedded self-complementary structures with a phase gradient in reflection, and demonstrate simultaneous implementation of anomalous reflection and polarization conversion with high efficiency.