Optically resonant dielectric nanostructures is a new direction in nanophotonic research which gives a strong promise to compliment or substitute plasmonics in many potential application areas . The main advantages of resonant dielectric nanostructures over conventional plasmonics are low losses, wide range of applicable dielectric materials and strong magnetic resonant response. So far most of research in this field has been conducted with silicon as a material for nanostructures due to its one of the highest value of refractive index at optical frequencies and CMOS compatibility. However, while silicon is an excellent material of choice for operation in the near-IR spectral range its applicability for visible frequencies is limited by increasing losses inside the material. Also, being an indirect bandgap semiconductor it is not a suitable material for making active nanoantenna devices. For these reasons in recent studies research focus starts shifting towards other appropriate materials such as III-V semiconductors, e.g. GaAs or GaP, and wide-bandgap semiconductors such as TiO2. In this presentation we will discuss applicability of different dielectric/semiconductor material platforms for obtaining resonant nanoantennas and metasurfaces operating in the visible frequency range. We will first show that titanium dioxide metasurfaces can be designed to obtain sharp resonances and full phase control at all three RGB wavelengths through Huygens’ metasurface approach, which pave the way towards realization of thin multi-layer metasurfaces with multi-colour operation. Then we will introduce a new III-V material platform based on GaN, which is highly transparent through the whole visible spectrum, and show high-efficiency operation of GaN metasurfaces in the blue and green parts of the visible spectrum. Finally we will discuss active nanoantennas based on GaAs and show the path towards achieving laser emission from resonant semiconductor nanoantenna structures.
1) A. I. Kuznetsov et al., “Optically resonant dielectric nanostructures”, Science 354, aag2472 (2016).
Graphene is one of the emerging active nanophotonics materials with optical properties that can be controlled in real time by an applied bias voltage. Different applications from sensing to active nanophotonics have been discussed in the literature recently and the field is still developing especially with an eye on structured and multi-layer graphene. To design new devices there is a need for precise modeling of multivariate and dynamic optical responses of graphene elements in frequency and time domains. Taking into account the complexity that comes along with multiple unknown parameters, including edge effects in nanostructured graphene elements, graphene impurities, imperfections of characterization optics etc., it is hard to build an adequate multivariate model to reach good quantitative agreement with experiment.
Here, we present an approach that uses optimization methods to retrieve the optical properties of a given graphene sample from experiment. We show that with these techniques good quantitative agreement with experiments can be achieved; additionally we encapsulate our techniques in an online data-fitting tool. The tool includes several options to precisely fit the conductivity function to a given experiment - general spline approximations and physically meaningful random phase approximation models for frequency domain solvers, along with the relaxed Lorentz oscillator models for confident time domain simulations. A pilot version of our free online tool entitled Photonics2D-Fit (to be staged at nanoHUB.org) is presented.