Plasmonic and metasurface nanostructures for optical imaging

Various optical imaging devices have been significantly developed as commercial products including digital cameras, smartphone displays, and three-dimensional microscopes in the electronic industry until now. Such a rapid development makes many people expect more advanced devices which may be not only multifunctional but also smaller and lighter. However, we cannot achieve it only by scaling down conventional optic systems due to the limits of inherent volume needed in classical optic parts. Nanophotonics can be a potential candidate to overcome the intrinsic problem. In particular, plasmonic and metasurface nanostructures have been briskly studied in recent years because they are able to control input lights within a few hundred nanometers of a thin layer. Here we introduce some representative cases of them for optical imaging. We firstly propose a cavity-aperture, which is comprised of a cavity and a metal nanoaperture, to change the color and intensity of the light transmitted through a single pixel. Because a cavity organizes various lights having different wavelengths and a nanoaperture spatially selects one of them without a serious distortion of a light field distribution, we can extract a light with a specific wavelength and amplitude using the cavity-aperture. Some metasurface nanostructures are also suggested for a broadband polarimeter, circular polarizer, directional switching, and holographic imaging. They are useful in dramatically miniaturizing optical devices due to their thin and compact sizes. We expect these plasmonic and metasurface nanostructures have a potential for advanced portable imaging systems.N