  Centuries of effort to improve imaging has focused on perfecting and
combining lenses to obtain better optical performance and new functionalities.
The arrival of nanotechnology has brought to this effort engineered surfaces
called metalenses, which promise to make imaging devices more compact. However,
unaddressed by this promise is the space between the lenses, which is crucial
for image formation but takes up by far the most room in imaging systems. Here,
we address this issue by presenting the concept of and experimentally
demonstrating an optical 'spaceplate', an optic that effectively propagates
light for a distance that can be considerably longer than the plate thickness.
Such an optic would shrink future imaging systems, opening the possibility for
ultra-thin monolithic cameras. More broadly, a spaceplate can be applied to
miniaturize important devices that implicitly manipulate the spatial profile of
light, for example, solar concentrators, collimators for light sources,
integrated optical components, and spectrometers.
