Diabolo Nanoantenna for Enhancing and Confining the Magnetic Optical Field

Abstract

In this Letter, we introduce a new nanoantenna concept aimed at generating a single magnetic hot spot in the optical frequency range, thus confining and enhancing the magnetic optical field on the background of a much lower electric field. This nanoantenna, designed by applying Babinet's principle to the bowtie nanoaperture, takes the shape of a diabolo. It differs from the well-known bowtie nanoantenna in that the opposing pair of metal triangles are electrically connected through their facing tips. Thus instead of a large charge density accumulating at the air gap of the bowtie nanoantenna, leading to a large electric field, a high optical current density develops within the central "metal gap" of the diabolo nanoantenna, leading to a large magnetic field. Numerical simulation results on the first nanodiabolo geometries show a 2900-fold enhancement of the magnetic field at a wavelength of 2540 nm, confined to a 40-by-40 nm region near the center of the nanoantenna.

Effect of gap width on enhanced magnetic optical fields in metallic split ring resonators

“…Even higher enhancement of the magnetic intensity is possible provided that the size of the SRR is increased to shift the magnetic resonance to a longer wavelength, 29 at which the losses in the metal could get smaller. It should be noted that although the magnetic field enhancement achieved in the SRRs could be much higher than that obtained from the metallic diabolo nanoantennas (the enhancement factor of 2950 at a wavelength of 2540 nm), 19 the electric field background in the diabolo structures is much lower than that in the SRRs. Such a highly enhanced magnetic field may have important applications in magnetic sensors or detectors, 16 magnetic nonlinearity and devices based thereon, [13][14][15] and inducing magnetic dipole transitions.…”

“…12 Considering the increasing attention towards the magnetic field enhancement stimulated by its potential applications in magnetic nonlinearity, [13][14][15] probing the vectorial magnetic near-fields, 16 and controlling magnetic dipole transition, 17 now the realization of a large amplification of magnetic field at optical frequencies is as important an issue in nanophotonics as achieving electric field enhancement. Recent work has shown that metallic nanowire and diabolo nanoantenna structures, 18,19 designed by applying Babinet's principle to the metallic structures such as nanogaps and nanobowties that were employed previously for achieving huge electric field enhancement, 20,21 can result in highly confined and enhanced localized magnetic fields. For example, magnetic field intensity enhancement by a factor of 2900 is predicted for the metallic diabolo nanoantenna structures at a wavelength of 2540 nm.…”

“…For example, magnetic field intensity enhancement by a factor of 2900 is predicted for the metallic diabolo nanoantenna structures at a wavelength of 2540 nm. 19 Another approach to enhance the local magnetic fields is to pattern artificial magnetic atoms into one-or two-dimensional arrays. [22][23][24] It has been shown that magnetic resonances in the periodic array of metallic wire pairs can be coupled to the waveguide modes and Bloch surface waves, 22 we have shown that when the coupling took place between the magnetic resonances and lattice surface modes arising from light diffraction in two-dimensional periodic arrays of metallic rodpairs, an enhancement factor as high as 450 could be achieved for magnetic field intensity at a visible wavelength of 780 nm.…”

Numerical conversion efficiency of thermally isolated Seebeck nanoantennas

“…19 Because the focus of this study is on the thermal isolation of the devices, their effects on conversion efficiency and their limits for harvesting applications, we select to arbitrarily analyze the simple case of dipole nanoantennas, even though higher conversion efficiencies are exhibited by different dipole geometries such as the tapered or the diabolo structures. 3,24 It is worth highlighting that the efficiency of the Seebeck nanoantennas is expected to increase further by proposing different geometries than the dipoles, but here, we evaluate the limits of thermal isolation and thermo-electric properties of metals. The proposed nanoantennas were tuned to recover the thermal wavelengths around 10.6 µm (28.3 THz).…”

Resonance spectra of diabolo optical antenna arrays

“…Previous works predicted that thinner metal film thicknesses and smaller central strip widths can produce larger magnetic field enhancement, with electromagnetic simulations indicating that this induces resonance wavelength red-shifts. 29 Previous studies also have found that the scattering and absorption cross sections of single metal bar optical antennas can be increased by narrowing the waist of diabolo bars and that the resonance shifts to longer wavelength by reducing the waist of metal bars. 30 However, these results are based on the numerical simulations.…”