Title: Generating Spatial Spectrum with Metasurfaces,
Abstract: Fourier optics, the principle of using Fourier Transformation to understand
the functionalities of optical elements, lies at the heart of modern optics,
and has been widely applied to optical information processing, imaging,
holography etc. While a simple thin lens is capable of resolving Fourier
components of an arbitrary optical wavefront, its operation is limited to near
normal light incidence, i.e. the paraxial approximation, which put a severe
constraint on the resolvable Fourier domain. As a result, high-order Fourier
components are lost, resulting in extinction of high-resolution information of
an image. Here, we experimentally demonstrate a dielectric metasurface
consisting of high-aspect-ratio silicon waveguide array, which is capable of
performing Fourier transform for a large incident angle range and a broad
operating bandwidth. Thus our device significantly expands the operational
Fourier space, benefitting from the large numerical aperture (NA), and
negligible angular dispersion at large incident angles. Our Fourier metasurface
will not only facilitate efficient manipulation of spatial spectrum of
free-space optical wavefront, but also be readily integrated into micro-optical
platforms due to its compact size.