Reprogrammable optical metasurfaces by electromechanical reconfiguration

Recent Advances in Tunable Metasurfaces and Their Application in Optics

Metasurfaces can be opportunely and specifically designed to manipulate electromagnetic wavefronts. In recent years, a large variety of metasurface-based optical devices such as planar lenses, beam deflectors, polarization converters, and so on have been designed and fabricated. Of particular interest are tunable metasurfaces, which allow the modulation of the optical response of a metasurface; for instance, the variation in the focal length of a converging metalens. Response tunability can be achieved through external sources that modify the permittivity of the materials constituting the nanoatoms, the substrate, or both. The modulation sources can be classified into electromagnetic fields, thermal sources, mechanical stressors, and electrical bias. Beside this, we will consider optical modulation and multiple approach tuning strategies. A great variety of tunable materials have been used in metasurface engineering, such as transparent conductive oxides, ferroelectrics, phase change materials, liquid crystals, and semiconductors. The possibility of tuning the optical properties of these metamaterials is very important for several applications spanning from basic optics to applied optics for communications, depth sensing, holographic displays, and biochemical sensors. In this review, we summarize the recent progress on electro-optical magnetic, mechanical, and thermal tuning of metasurfaces actually fabricated and experimentally tested in recent years. At the end of the review, a short section on possible future perspectives and applications is included.

Nano-kirigami enabled chiral nano-cilia with enhanced circular dichroism at visible wavelengths

Nano-kirigami method enables rich diversity of structural geometries that significantly broaden the functionalities of optical micro/nano-devices. However, the methodologies of various nano-kirigami are still limited and as a result, the chiral nano-kirigami structure has yet been pushed to the limit for operation at visible wavelength region. Here, the merits of the various nano-kirigami strategies are comprehensively explored and bio-inspired nano-cilia metasurface with enhanced circular dichroism at visible wavelengths is demonstrated. The stereo chiral nano-cilia metasurface is designed with three-fold rotational symmetry, which exhibits tuneable chiroptical responses when the nano-cilia are deformed to form strong chiral light-matter interactions. By employing electron-beam lithography (EBL) and focused ion beam (FIB) lithography, on-chip nano-cilia metasurfaces are experimentally realized in near-infrared wavelengths region and at visible wavelengths, respectively, successfully validating the giant circular dichroism revealed in simulations. Our work is useful to broaden the existing platform of micro/nano-scale manufacturing and could provide an effective method for the realization of versatile bioinspired nanostructures with profound chiroptical responses.