Broadband spin-unlocked metasurfaces for bifunctional wavefront manipulations

Recently, Pancharatnam–Berry (PB) metasurfaces have exhibited powerful capabilities to control spin-polarized light. However, the adopted abrupt PB phase, introduced by simply rotating the basic elements, is spin-locked with opposite signs for different spin excitations, greatly limiting their practical applications. Here, we introduce a high-efficiency and broadband spin-unlocked metasurface with two mechanisms of a resonance phase and a geometric phase perfectly combined together. The design strategy is quite simple just through changing one geometric parameter rather than multi parameter optimization. As a proof of concept, the anomalous photonic spin Hall effect based on the spin-unlocked metasurface is demonstrated first, showing high experimental efficiency (over 80%) in a broad frequency range (11.3–16.6 GHz). Furthermore, another spin-unlocked metasurface is built to demonstrate the completely independent wavefront manipulations, i.e., the focusing effect and anomalous reflection. These findings significantly expand the electromagnetic control ability of a metasurface.