High-Resolution and Ultralow-Power Nonlinear Image Processing with Passive High-Quality Factor Metasurfaces

Image processing is one of the most exciting domains for applying artificial intelligence but is computationally expensive. Nanostructured metasurfaces have opened the door to the ultimate energy saving by directly processing ambient image data via ultrathin layers before detection. However, a key ingredient of universal computation─nonlinear thresholding functions─have yet to be demonstrated for low intensities without an external power source. Here, we present a passive, all-optical method for nonlinear image processing using silicon nanoantenna arrays. We experimentally demonstrate an intensity thresholding filter capable of processing one-dimensional images with only watt-level power. By leveraging the opto-thermal nonlinearity through high-Q guided mode resonance, we achieve an experimental threshold as low as 0.1 mW/μm² with a spatial resolution of 1.85 μm. Additional simulations indicate that the threshold can be further reduced while maintaining high spatial selectivity. Analog, pixel-wise, smoothed leaky ReLU activation filters promise to revolutionize image sensing.