Metasurface enabled broadband, high numerical aperture Laplace differentiator under multiple polarization illumination

Abstract

Abstract Optical metasurfaces to perform optical analog spatial differentiation operations and image edge detection processing is a currently hot topic. However, some metasurface differentiators are limited by polarization dependence, narrow operating bandwidth, low numerical aperture (NA), requiring for additional polarization elements or digital processing, and under coherent light illumination conditions. Here, we use the optical angular dispersion effect based on resonant dielectric metasurface, to realize the Laplacian differential operation in the real space directly, which can address these critical metrics for p- and s-polarized light. Moreover, the broadband operating range of the metasurface differentiator can be obtained by exciting and detuning the electric toroidal dipole (ETD) and magnetic toroidal dipole (MTD) resonances. We experimentally demonstrate that azimuthal-insensitive Laplace differential operations and dual-polarization second-order two-dimensional edge detection with NA up to 0.64 and spectral bandwidths of nearly 100 nm from 750 to 850 nm. In addition, broadband incoherent and unpolarized edge detection experiments are also carried out with satisfactory performance. Our work will pave the way for free-space realization of high-efficiency, broadband parallel optical-computation and image-processing in machine-vision, biomedical, and optical microscopy.

Keywords

• Metasurface
• Laplace differentiator
• Edge detection
• Toroidal dipole resonance