Metasurface-enabled Broadband All-Optical Edge Detection in Visible Frequencies

Abstract

Abstract Image processing is of fundamental importance for numerous modern technologies including AR/VR glasses, autonomous driving, and biometric identification. In recent years, due to increasing demand for real-time, continuous data processing, metamaterial and metasurface based all-optical computation techniques emerged as a promising alternative to digital computation. Most of the pioneer research focused on all-optical edge detection as a fundamental step of image processing. Metasurfaces have been shown to enable real time edge detection with low to no power consumption. However, the previous demonstrations were subjected to the several limitations such as need for oblique-incidence, polarization dependence, need for additional polarizers, narrow operation bandwidth, being limited with processing in 1D, operation with coherent light only, and requiring digital post-processing. Here, we propose and demonstrate metasurfaces for 2D isotropic and polarization independent edge detection based on Fourier optics principles that overcome aforementioned limitations and challenges. Our proposed metasurface platform consists of co-centric metallic rings that enable carefully chosen spatial transmission profile matching the Fourier transformation of the second-order differentiation. We experimentally confirm polarization-independent, broadband edge detection with high transmission efficiency under both coherent and incoherent illumination along the visible frequency range. Additional simulations and measurements in the near-IR wavelength range confirmed edge detection by the same metasurface, indicating broadband operation capability. Our approach addresses several challenging tasks at once and therefore paves the path towards the application of metasurfaces for real-life image processing and all-optical computation tasks.