Abstract
The interest in plasmonic electro-optical modulators with nanoscale footprint and ultrafast low-energy performance has generated a demand for precise multiphysics modeling of the electrical and optical properties of plasmonic nanostructures. We perform combined simulations that account for the interaction of highly confined nearfields with charge accumulation and depletion on the nanoscale. Validation of our numerical model is done by comparison to a recently published reflective meta-absorber. The simulations show excellent agreement to the experimental mid-infrared data. We then use our model to propose electro-optical modulation of the extinction cross-section of a gold dimer nanoantenna at the telecom wavelength of 1550 nm. An ITO gap-loaded nanoantenna structure allows us to achieve a normalized modulation of 45% at 1550 nm, where the gap-load design circumvents resonance pinning of the structure. Resonance pinning limits the performance of simplistic designs such as a uniform coating of the nanoantenna with a sheet of indium tin oxide, which we also present for comparison. This large value is reached by a reduction of the capacitive coupling of the antenna arms, which breaks the necessity of a large volume overlap between the charge distribution and the optical nearfield. A parameter exploration shows a weak reliance on the exact device dimensions, as long as strong coupling inside the antenna gap is ensured. These results open the way for a new method in electro-optical tuning of plasmonic structures and can readily be adapted to plasmonic waveguides, metasurfaces and other electro-optical modulators.
Highlights
Nanoplasmonic components are of interest for their potential of achieving enhanced light-matter interaction through confinement of electromagnetic fields below the diffraction limit
We have developed a numerical electro-optical model that describes the nanoscale electroplasmonic response of nanoantenna switches
To find novel approaches in implementing plasmonic electro-optical modulation, we adapted our model to a geometry of gold dimer nanoantennas under an electrical bias
Summary
Nanoplasmonic components are of interest for their potential of achieving enhanced light-matter interaction through confinement of electromagnetic fields below the diffraction limit. On-chip integrated photonic circuits require new forms of control of light at length scales compatible with the footprint of traditional nanoelectronic circuits. Due to their high near-field confinement, plasmonic structures are highly sensitive to their surrounding medium. Electrical tuning of plasmonic devices has opened the door to new applications in optical circuits and tunable metasurfaces. Examples for such devices are hybrid waveguides with plasmonic coatings, which are switched by an applied bias between low absorption (on-state) and high absorption (off-state) [3,4,5,6,7,8]. Electrical modulation is of great interest for the realization of tunable metasurfaces, such as thin film reflectors [9,10,11,12]
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