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High‐resolution image sensing technologies have exploded over the past decade. A critical capability of all image sensors is to separate light into its individual color components. In most technologies today, this is done via color filters. Filters, however, intrinsically waste a large fraction of the light by absorption or scattering. This affects image sensor performance, because the amount of light incident on each image sensor pixel reduces quadratically with linear scaling of pixel size. This is particularly detrimental to the performance of (sub‐)wavelength size pixels. Herein, a conceptually novel approach is provided for color functionality in image sensors, by designing a color router that achieves perfect RGB‐IR color routing for sub‐wavelength size pixels. In a color router, all incident light for each color channel is routed directly and without loss to the photodetector of the corresponding color channel pixel. It is shown that color routers can be designed to near‐perfectly match a prescribed spectral shape, which is important for color image processing. It is further shown that these routers are designed to achieve specific spectral bandwidth and to meet angular as well as fabrication constraints.

Photonic structures have great potential in creating novel computing hardware due to their fast processing speed, low energy cost, and massive parallelism. Many algorithms in image processing and neural networks rely heavily on convolution and will benefit from efficient optical implementation of convolution. Here we propose meta-crystal slabs for a general implementation of optical convolution. Through an optimization approach, we design structures to perform a wide variety of convolution kernels. In particular, we numerically demonstrate several low-order differentiation kernels with a Gaussian envelope operating in transmission in the normal direction. Our structures are very compact and compute directly on the incident image fields. Our work may lead to high-performance optical computing hardware, and it also points to the possibility of creating novel optical components with volumetric metamaterials for imaging and sensing applications.

We analyze scattering properties of twisted bilayer photonic crystal slabs through a high-dimensional plane wave expansion method, which does not involve super-cell approximation, and explain the spectrum with an intuitive correspondence relation.