Transmissive Ultrathin Pancharatnam-Berry Metasurfaces with nearly 100% Efficiency

Devices for manipulating spin-polarized light in $t\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}m\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n$ (not reflection) mode are highly desired in photonics research. To this end, the authors craft a Pancharatnam-Berry metasurface of subwavelength thickness $\ensuremath{\lambda}/8$ with a 91% efficient photonic spin Hall effect, at microwave frequencies. Key to this result is the magnetic response of the constituent meta-atoms. These findings open up the control of spin-polarized light using spin-dependent metaholograms, polarization modulators, or chirality-controlled surface-plasmon couplers, for example.