Multi-Color\nSpaceplates in the Visible

The\nultimate miniaturization of any optical system relies on the\nreduction or removal of free-space gaps between optical elements.\nRecently, nonlocal flat optic components named “spaceplates”\nwere introduced to effectively compress space for light propagation.\nHowever, space compression over the visible spectrum remains beyond\nthe reach of current spaceplate designs due to their inherently limited\noperating bandwidth and functional inefficiencies in the visible range.\nHere, we introduce “multi-color” spaceplates performing\nachromatic space compression at three distinct color channels across\nthe visible spectrum to markedly miniaturize color imaging systems.\nIn this approach, we first design monochromatic spaceplates with high\ncompression factors and high transmission amplitudes at visible wavelengths\nbased on a scalable structure and dielectric materials widely used\nin the fabrication of meta-optical components. We then show that the\ndispersion-engineered combination of monochromatic spaceplates with\nsuitably designed transmission responses forms multicolor spaceplates\nthat function achromatically. The proposed multicolor spaceplates,\ncomposed of amorphous titanium dioxide and silicon dioxide layers,\nefficiently replace free-space volumes with compression ratios as\nhigh as 4.6, beyond what would be achievable by a continuously broadband\nspaceplate made of the same materials. Our strategy for designing\nmonochromatic and multicolor spaceplates, along with the presented\ntheoretical and computational results, show that strong space-compression\neffects can be achieved in the visible range. Our findings may ultimately\nenable a new generation of ultrathin optical devices for various applications.