We design large aperture, all-silicon meta-optic doublets for unidirectional and synergistic imaging at a wavelength of 4 μm. 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 focus an incoming plane wave only when its 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.
We investigate correlations between the configuration statistics of random metasurfaces and their spectral response. Our metasurfaces consist of a two-dimensional array of silicon nanopillars with widths sampled from a normal distribution placed on a silica substrate. We explore the effect of tuning the parameters characterizing the distribution of nanopillar widths on the wavelength-dependent transmissivity of the random metasurface in the 400 – 800 nm wavelength range. This analysis helps us create a direct mapping between the parameters of the nanopillar width distribution and the spectral responses of the random metasurfaces. We exploit this mapping to design a photonic device encoding spectrally encrypted image data in the visible wavelength range. Our findings offer new insight into the optical properties of random media and provide avenues for developing such systems for a broad range of applications.
Conventional imaging systems are usually composed of bulky glass optics, and while they work well for many applications, they offer little functionality in applications where system size is a constraint. Optical metasurfaces provide a thin and light-weight alternative to conventional bulky optical elements by manipulating light scattering via resonant nanostructures. The inherent diffractive nature of metalenses induces severe chromatic aberrations when imaging under broadband illumination, which limits their potential applications where multi-color information is important. In this work, we present an alternative metalens plus computational design where the point spread function is engineered to be spectrally invariant to reduce chromatic aberrations and enables computational reconstruction of a measurement using a single digital filter. The created lenses have a numerical aperture of ~0.45 and generate in-focus images under whitelight illumination.
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