Spin-selective reflection manipulation enabled by plasmonic guided mode resonance in out-of-plane folded metamirrors

Out-of-plane plasmonic chiral systems exhibit considerable advantages in amplifying and manipulating chiroptical phenomena, thanks to their readily accessible intrinsic chirality. Here, we develop a chiral metamirror with an out-of-plane folded design, based on the nano-kirigami method. By introducing out-of-plane mirror symmetry breaking, the nonlocal plasmonic guided mode resonances (GMRs), contributed by the handedness-dependent co-excitation of magnetic dipoles and electric quadrupoles, are excited within the Fabry-Perot cavity, enabling spin-selective reflection. This phenomenon is attributed to the spin-selective collective interference of enhanced magnetic fields caused by strong interlayer coupling. Through a simple adjustment of the out-of-plane structural height, the excitation intensity of magnetic fields for uncoupled circularly polarized light (CPL) can be continuously controlled, while leaving the coupled CPL unaffected. This capability allows for independent manipulation of the reflection amplitude with spin selectivity, which has potential applications in spin-selective optical encryption, as demonstrated by the gradient imaging results. Meanwhile, the resonant wavelength of the coupled CPL can be proportionally adjusted with variations in the refractive index of the dielectric layer, thereby enabling individual regulation of the operating wavelength of the chiral mirror. This straightforward and controllable out-of-plane deformation mechanism for manipulating the excitation intensity of GMRs provides valuable methodologies for realizing optical polarization selectivity and holds promise for applications in the fields of optical information transfer, optical imaging, optical computing, etc.