Optical computing using photonic crystal slabs

We discuss the use of photonic crystal slab to accomplish a number of imaging processing tasks, including edge detection, image smoothing, white noise suppression and, suppression or extraction of periodic features. All these tasks involve filtering in the wavevector domain. Image filtering can be implemented electronically. However, in big-data applications requiring real-time and high-throughput image filtering, conventional digital computations become challenging. Nanophotonics-based optical analog computing may overcome this challenge by offering high-throughput low-energy-consumption filtering using compact devices. Here, we show that several types of isotropic two-dimensional image filters can be implemented with a single photonic crystal slab device. Such a device is carefully designed so that the guided resonance near the Γ point exhibits an isotropic band structure. Depending on the light frequency and the choice of transmission or reflection mode, this compact device realizes isotropic high-pass (Laplacian), low-pass, band-reject and band-pass filtering in the wavevector domain. We numerically demonstrate various important image processing tasks enabled by these filters as mentioned above. Our work points to new opportunities in optical analog computing as provided by nanophotonic structures.