Transmissive Ultrathin Pancharatnam-Berry Metasurfaces with nearly 100% Efficiency

Pancharatnam-Berry (PB) metasurfaces exhibit strong abilities to control spin-polarized light, but transmission-mode PB functional devices exhibiting simultaneously nearly 100% efficiencies and ultrathin thicknesses are rarely seen. Here, we show that 100%-efficiency photonic spin Hall effect (PSHE) can be realized in ultrathin PB metasurfaces exhibiting both electric and magnetic responses satisfying certain criteria, and then we design and fabricate a microwave transmissive PB metasurface with thickness of approximately lambda/8 yet exhibiting a maximum PSHE efficiency of approximately 91% in experiments (approximately 94% in full-wave simulations). Our results can stimulate the realizations of high-performance PB metadevices with diversified functionalities at different frequencies. As an example, we fabricate several vortex-beam generators and demonstrate that they not only exhibit ultrahigh working efficiencies but also are immune from normal-mode background interferences.