Georgia T. Papadakis

Nanoscale Conducting Oxide PlasMOStor

We experimentally demonstrate an ultracompact PlasMOStor, a plasmon slot waveguide field-effect modulator based on a transparent conducting oxide active region. By electrically modulating the conducting oxide material deposited into the gaps of highly confined plasmonic slot waveguides, we demonstrate field-effect dynamics giving rise to modulation with high dynamic range (2.71 dB/μm) and low waveguide loss (∼0.45 dB/μm). The large modulation strength is due to the large change in complex dielectric function when the signal wavelength approaches the surface plasmon resonance in the voltage-tuned conducting oxide accumulation layer. The results provide insight about the design of ultracompact, nanoscale modulators for future integrated nanophotonic circuits.

Field-effect induced tunability in hyperbolic metamaterials

We demonstrate that use of the field effect enables tuning of the effective optical parameters of a layered hyperbolic metamaterial at optical frequencies. Field-effect gating electrically modulates the permittivity in transparent conductive oxides via changes in the carrier density. These permittivity changes lead to active modulation of the effective electromagnetic parameters along with active control of the anisotropic dispersion surface of hyperbolic metamaterials and enable the opening and closing of photonic band gaps. Tunability of the effective electric permittivity and magnetic permeability also leads to topological transitions in the optical dispersion characteristics.

Retrieval of material parameters for uniaxial metamaterials

We present a general method for retrieving the effective tensorial permittivity of uniaxially anisotropic metamaterials. By relaxing the usually imposed constraint of assuming nonmagnetic metal/dielectric metamaterials, we also retrieve the effective permeability tensor and show that multilayer hyperbolic metamaterials exhibit a strong and broadband diamagnetic response in the visible regime. The method provides the means for designing magnetically anisotropic metamaterials for studying magnetic topological transitions in the visible regime. We obtain orientation-independent effective material parameters, which are distinguishable from mere wave parameters. We analytically validate this method for Ag/SiO_2 planar metamaterials with a varying number of layers and filling fractions and compare to the results from effective medium theory and Bloch theory.

Optical magnetism in planar metamaterial heterostructures

Harnessing artificial optical magnetism has previously required complex two- and three-dimensional structures, such as nanoparticle arrays and split-ring metamaterials. By contrast, planar structures, and in particular dielectric/metal multilayer metamaterials, have been generally considered non-magnetic. Although the hyperbolic and plasmonic properties of these systems have been extensively investigated, their assumed non-magnetic response limits their performance to transverse magnetic (TM) polarization. We propose and experimentally validate a mechanism for artificial magnetism in planar multilayer metamaterials. We also demonstrate that the magnetic properties of high-index dielectric/metal hyperbolic metamaterials can be anisotropic, leading to magnetic hyperbolic dispersion in certain frequency regimes. We show that such systems can support transverse electric polarized interface-bound waves, analogous to their TM counterparts, surface plasmon polaritons. Our results open a route for tailoring optical artificial magnetism in lithography-free layered systems and enable us to generalize the plasmonic and hyperbolic properties to encompass both linear polarizations.Most natural materials do not have a magnetic response at optical frequencies and inducing optical magnetism by metamaterials typically requires complex nanostructures. Here, Papadakis et al. show that artificial optical magnetism can also be achieved with planar multilayer metamaterials.