Spin-dependent intensity-adjustable phase-change metalenses

Metasurfaces, artificial subwavelength planar structures based on anisotropic units, manifest an unparalleled ability in manipulating the amplitude, phase and polarization of the incident electromagnetic (EM) waves, thus enabling arbitrary modulation of wavefront. As of the most metasurface embodiments, metalenses have aroused great interest of researchers by virtue of their extraordinary wavefront manipulation, ultracompact size, versatility and high compatibility with semiconductor processes. However, current approaches are mostly restricted by predefined phase profiles, disabling polarization multiplexing and intensity-adjustable focusing performance simultaneously. Moreover, the functionalities of metalens are immediately locked once the structure is determined, seriously hindering their broader potential applications. To this end, two Ge₂Sb₂Se₄Te₁-assisted spin-decoupled metalenses are proposed, which enable completely transverse or longitudinal spin-dependent split focusing upon the illumination of left-/right-handed circularly polarized (LCP or RCP) light by synergizing PB and propagation phase. Since the spin-dependent focusing are susceptible to the polarization states of incidence, the relative intensity of split focal spots can be controlled by manipulating the weights of LCP and RCP component, leading to the intensity-adjustable virtue. Furthermore, the focusing performance of our scheme can be continuously tuned and ultimately realize dynamically switching of "ON" and "OFF" states by actuating GSST from amorphous transiting into crystalline state, showing huge potential applications in the fields of spin-controlled nanophotonics, optical imaging and optical sensors.