Vector-Beam Nonlocal Metasurfaces Controlling Local Geometric Phase

Recent advancements have enabled nonlocal metasurfaces (MSs) to manipulate wavefronts spatially and spectrally [A.C. Overvig and A. Alù, “Diffractive Nonlocal Metasurfaces,” Laser Photonics Rev., vol. 16, 2100633, Jul. 2022]. The bilayer configuration of such nonlocal MSs provides control over quality-factor and geometric phase for arbitrary polarizations [A. Overvig, Y. Kasahara, G. Xu, and A. Alù, “Demonstration of a polarization-agnostic geometric phase in nonlocal metasurfaces,” arXiv, Feb. 25, 2023], enabling local geometric phase manipulation for any polarization state, including linear and elliptical polarization. Such flexibility offers the possibility of controlling the geometric phase for vector beams, optical beams characterized by spatially varying polarization states across their cross-section. The generation of vortex vector beams has been demonstrated using local MSs [Y. Bao, J. Ni, C. Qiu, “A Minimalist Single-Layer Metasurface for Arbitrary and Full Control of Vector Vortex Beams,” Adv. Mater., vol. 32, no. 6, 1905659], which, however, lack spectral shaping capabilities, notable feature of the nonlocal MSs.