Tunable all-dielectric metasurface for phase modulation of the reflected and transmitted light via permittivity tuning of indium tin oxide

We propose an electrically tunable metasurface, which can achieve relatively large phase modulation in both reflection and transmission modes (dual-mode operation). By integration of an ultrathin layer of indium tin oxide (ITO) as an electro-optically tunable material into a semiconductor-insulator-semiconductor (SIS) unit cell, we report an approach for active tuning of all-dielectric metasurfaces. The proposed controllable dual-mode metasurface includes an array of silicon (Si) nanodisks connected together via Si nanobars. These are placed on top of alumina and ITO layers, followed by a Si slab and a silica substrate. The required optical resonances are separately excited by Si nanobars in reflection and Si nanodisks in transmission, enabling highly confined electromagnetic fields at the ITO-alumina interface. Modulation of charge carrier concentration and refractive index in the ITO accumulation layer by varying the applied bias voltage leads to 240° of phase agility at an operating wavelength of 1696 nm for the reflected transverse electric (TE)-polarized beam and 270° of phase shift at 1563 nm for the transmitted transverse magnetic (TM)-polarized light. Independent and isolated control of the reflection and transmission modes enables distinctly different functions to be achieved for each operation mode. A rigorous coupled electrical and optical model is employed to characterize the carrier distributions in ITO and Si under applied bias and to accurately assess the voltage-dependent effects of inhomogeneous carrier profiles on the optical behavior of a unit cell

Excitation of Discrete and Continuous Spectrum in Subdiffraction Wire-Medium Type Lenses

Subwavelength imaging of the near field of a magnetic line-source excitation is studied for several wire-medium (WM) lens topologies using complex-plane analysis of the radiation integral. Nonlocal homogenization is used for the wire medium, resulting in an analytical expression for the transfer function of the lens. It is shown that by evaluating the Sommerfeld integral of the transmitted field in terms of the discrete and continuous spectra provides a general framework for better understanding of electromagnetic phenomena involved with subwavelength imaging. Results are obtained for a WM slab, and for a wire medium loaded with graphene monolayers and periodic arrays of graphene patches, demonstrating the interplay of the discrete and continuous spectral components in different operating regimes of the lenses. The imaging with a stack of silver slabs is also considered for comparison purposes.NASA NNX13AB31AMinisterio de Economía y Competitividad TEC2013-41913-PJunta de Andalucía P12-TIC-143

Tunable all-dielectric metasurface for phase modulation of the reflected and transmitted light via permittivity tuning of indium tin oxide

We propose an electrically tunable metasurface, which can achieve relatively large phase modulation in both reflection and transmission modes (dual-mode operation). By integration of an ultrathin layer of indium tin oxide (ITO) as an electro-optically tunable material into a semiconductor-insulator-semiconductor (SIS) unit cell, we report an approach for active tuning of all-dielectric metasurfaces. The proposed controllable dual-mode metasurface includes an array of silicon (Si) nanodisks connected together via Si nanobars. These are placed on top of alumina and ITO layers, followed by a Si slab and a silica substrate. The required optical resonances are separately excited by Si nanobars in reflection and Si nanodisks in transmission, enabling highly confined electromagnetic fields at the ITO-alumina interface. Modulation of charge carrier concentration and refractive index in the ITO accumulation layer by varying the applied bias voltage leads to 240° of phase agility at an operating wavelength of 1696 nm for the reflected transverse electric (TE)-polarized beam and 270° of phase shift at 1563 nm for the transmitted transverse magnetic (TM)-polarized light. Independent and isolated control of the reflection and transmission modes enables distinctly different functions to be achieved for each operation mode. A rigorous coupled electrical and optical model is employed to characterize the carrier distributions in ITO and Si under applied bias and to accurately assess the voltage-dependent effects of inhomogeneous carrier profiles on the optical behavior of a unit cell

Composite Multilayer Shared-Aperture Nanostructures: A Functional Multispectral Control

There is a growing demand in the field of metasurfaces to design and implement functional multispectral devices capable of complex beam conversion and high-capacity optical information processing. Control over the size of the aperture footprint, fabrication complexity, and fundamental cross-talk poses great challenges toward the realization of these multifunctional multispectral optical devices. Here, we demonstrate a systematic design strategy and a full roadmap toward implementation of a novel class of nanoantenna arrays based on the multilayer shared-aperture concept, which can simultaneously multiplex multiwavelengths into a single optical device platform. The idea is supported by engineering two dual-layer metasurface-based designs with the capability of superdistinct operating channels (lying in the thermal infrared and visible spectra) and superclose operating channels (both lying in the visible spectrum) to simultaneously and independently perform anomalous or similar wavefront manipulation at two predesigned wavelengths. We leverage transparent conducting oxide (TCO)–dielectric and plasmonic–dielectric composite multilayer nanostructures to realize the aforementioned designs, respectively. The challenges such as coupling effects among the different wavelengths, compactness, fabrication feasibility, and material frequency dispersion are thoroughly addressed by careful selection of constituent materials and geometrical shape of resonators, array architecture, and optimization of structural parameters of inclusions. As a proof of concept, we have designed two dual-wavelength holographic metalenses generating images located in-plane and out-of-plane at two selected wavelengths. The proposed technique is in particular of interest in the fields of data storage, information processing, and displays

Model Order Reduction of Large-Scale Metasurfaces Using a Hierarchical Dipole Approximation

Advances in the field of metasurfaces require simulation of large-scale metasurfaces that extend over many light wavelengths. Adopting standard numerical methods leads to models featuring a large number of degrees of freedom, which are prohibitive to solve within a time window compatible with the design workflow. Therefore, this demands developing the techniques to replace large-scale computational models with simpler ones, still capable of capturing the essential features but imposing a fraction of the initial computational costs. In this work, we present a simulation approach in order to handle reduced order analyses of large-scale metasurfaces of arbitrary elements. We use the discrete dipole approximation in conjunction with the discrete complex image method and hierarchical matrix construction as a common theoretical framework for dipole approximation in the hierarchy of individual elements and the array scale. We extract the contributions of multipoles in the scattering spectra of the nanoantennas forming the metasurface and retrieve their dynamic polarizabilities. The computational complexity of modeling the array problem is then significantly reduced by replacing the fine meshing of each nanoantenna with its dynamic polarizability. The solver is developed to model several fully functional metasurfaces of different types including a one-atom-thick metasurface made of graphene with chemical doping interruptions, a multifocusing lens made of plasmonic V-shaped nanoantennas, and a multicolor hologram consisting of dielectric nanobars. The performance of the method is evaluated through comparison with full-wave simulations, and a significant computational gain is observed while the accuracy of the results is retained owing to the preserved coupling information between dipolar modes

Tunable all-dielectric metasurface for phase modulation of the reflected and transmitted light via permittivity tuning of indium tin oxide

We propose an electrically tunable metasurface, which can achieve relatively large phase modulation in both reflection and transmission modes (dual-mode operation). By integration of an ultrathin layer of indium tin oxide (ITO) as an electro-optically tunable material into a semiconductor-insulator-semiconductor (SIS) unit cell, we report an approach for active tuning of all-dielectric metasurfaces. The proposed controllable dual-mode metasurface includes an array of silicon (Si) nanodisks connected together via Si nanobars. These are placed on top of alumina and ITO layers, followed by a Si slab and a silica substrate. The required optical resonances are separately excited by Si nanobars in reflection and Si nanodisks in transmission, enabling highly confined electromagnetic fields at the ITO-alumina interface. Modulation of charge carrier concentration and refractive index in the ITO accumulation layer by varying the applied bias voltage leads to 240° of phase agility at an operating wavelength of 1696 nm for the reflected transverse electric (TE)-polarized beam and 270° of phase shift at 1563 nm for the transmitted transverse magnetic (TM)-polarized light. Independent and isolated control of the reflection and transmission modes enables distinctly different functions to be achieved for each operation mode. A rigorous coupled electrical and optical model is employed to characterize the carrier distributions in ITO and Si under applied bias and to accurately assess the voltage-dependent effects of inhomogeneous carrier profiles on the optical behavior of a unit cell