Disordered Meta-Doublets for Unidirectional and Synergistic Imaging in The Mid–Infrared

Recent advances in metamaterials have enabled the realization of complex optical functionalities within a compact form factor. The vast number of design degrees of freedom in such systems provides the ability to manipulate optical waves in the spatial and spectral domain, thereby enabling the development of photonic devices for a broad range of applications. Here, we propose an all-silicon metamaterial platform for advanced imaging applications in the mid-infrared wavelength range. Specifically, we design large aperture, all-silicon meta-optic doublets for unidirectional and synergistic imaging at a wavelength of 4 μm. The large design space afforded by metamaterials often makes it challenging to optimize such devices for a desired functionality using a conventional forward design approach. Here we develop a differentiable model that maps the structure of our meta-atoms to their optical response. Our algorithm uses this model iteratively to modify the structural parameters of our devices and optimize a figure of merit that mathematically describes the desired optical response. The phase profiles of our optimized devices possess a large degree of disorder that is tailored to realize the required imaging functionality. When illuminated by a plane wave in the forward mode, our unidirectional imager generates an intense spot on its optic axis at a predefined focal length. In the reverse mode, the imaging performance is significantly reduced, accompanied by a dramatic reduction in light intensity on the focal plane. On the other hand, our synergistic imager is optimized to enable imaging only when the constituent meta-optics are used in conjunction with each other. We envision our devices to provide new avenues for the development of metamaterial imaging platforms for applications in defense and data security.