Phase-change nonlocal metasurfaces for dynamic wave-front manipulation

Recent advances in nonlocal metasurfaces have enabled unprecedented success in shaping the wave front of light with spectral selectivity, offering alternative solutions for many emerging nanophotonics applications. The ability to tune both the spectral and spatial properties of such a class of metasurfaces is highly desirable, but the dynamic nonvolatile control remains elusive. Here, we demonstrate active narrowband wave-front manipulation by harnessing quasi-bound states in the continuum (quasi-BICs) in phase-change nonlocal metasurfaces. The proof-of-principle metasurfaces made of ${\mathrm{Sb}}_{2}{\mathrm{S}}_{3}$ allow for nonvolatile, reversible, and tunable spectral control over wave front and switchable spatial response at a given wavelength in the near-infrared regime. The design principle mainly builds upon the combination of the geometry phase of quasi-BICs and the dynamic tunability of phase-change meta-atoms to tailor the spatial response of light at tunable resonant wavelengths. By tuning the crystallization level of ${\mathrm{Sb}}_{2}{\mathrm{S}}_{3}$ meta-atoms through controlling the external stimuli, the dynamic nonlocal wave-front-shaping functionalities of beam steering, one-dimensional, and two-dimensional focusing, and holographic imaging are achieved exclusively at resonant wavelengths, with functionally transparent off resonance. This work represents a critical advance towards developing an integrated dynamic nonlocal metasurface for future augmented and virtual reality wearables.