Imaging with an Ultrathin Reciprocal Lens

Abstract

Imaging is of great importance in everyday life and various fields of science and technology. Conventional imaging is achieved by bending light rays originating from an object with a lens. Such ray bending requires space-variant structures, inevitably introducing a geometric center to the lens. To overcome the limitations arising from the conventional imaging mechanism, we consider imaging elements that employ a different mechanism, which we call reciprocal lenses. This type of imaging element relies on lateral ray shifting, enabled by momentum-space-variant phase modulations in periodic structures. As such, it has the distinct advantage of not requiring alignment with a geometric center. Moreover, upright real images can be produced directly with a single reciprocal lens as the directions of rays are not changed. We realize an ultrathin reciprocal lens based on a photonic crystal slab. We characterize the lateral ray shifting behavior of the reciprocal lens and demonstrate imaging. Our work gives an alternative mechanism for imaging and provides a new way to modulate electromagnetic waves.