Broadband spin-multiplexed single-celled metasurface holograms: a comprehensive comparison between different strategies.

Metasurface-generated holograms have emerged as a unique platform for arbitrarily shaping the reflected/transmitted wavefronts with the advantages of subwavelength large pixel sizes and multiple information channels. However, achieving multiple holographic images with large operation bandwidths is a rather complicated and arduous issue due to the dissimilar dispersion of all meta-atoms involved. In this work, we design and experimentally demonstrate single-celled metasurfaces to realize broadband and spin-multiplexed holograms, whose phase modulation is based only on the geometric phase supplied by a judiciously designed high-performance nanoscale half-wave plate operating in reflection. Four different multiplexing strategies are implemented, and the resulting holograms are systemically assessed and compared with respect to background levels, image fidelities, holograms efficiencies, and polarization conversion ratios. Our work complements the methodologies available for designing multiplexed meta-holograms with versatile functionalities.