Abstract
We present numerical simulations of low aspect ratio gallium phosphide nanowires under plane wave illumination, which reveal the interplay between transverse and longitudinal antenna-like resonances. A comparison to the limiting case of the semiconducting sphere shows a gradual, continuous transition of resonant electric and magnetic spherical Mie modes into Fabry-Pérot cavity modes with mixed electric and magnetic characteristics. As the length of the nanowires further increases, these finite-wire modes converge towards the leaky-mode resonances of an infinite cylindrical wire. Furthermore, we report a large and selective enhancement or suppression of electric and magnetic field in structures comprising two semiconducting nanowires. For an interparticle separation of 20 nm, we observe up to 300-fold enhancement in the electric field intensity and an almost complete quenching of the magnetic field in specific mode configurations. Angle-dependent extinction spectra highlight the importance of symmetry and phase matching in the excitation of cavity modes and show the limited validity of the infinite wire approximation for describing the response of finite length nanowires toward glancing angles.
Highlights
Research into nanophotonic devices is thriving, with advances in technology pushing the limits of what we can fabricate
We have investigated the optical modes of low aspect ratio nanowires in relation to the fundamental Mie resonances of a sphere and the radial Mie/leaky mode resonances of an infinite cylindrical wire
In addition it is found that, both for transverse magnetic (TM) and transverse electric (TE) polarizations, the magnetic b-type Mie resonances are at the origin of both the electrical and magnetic radial eigenmodes of the infinite wire
Summary
Research into nanophotonic devices is thriving, with advances in technology pushing the limits of what we can fabricate. We investigate the underlying symmetries of low aspect ratio dielectric nanowires by means of numerical calculations to address the detailed mode structure that connects the Mie-scattering regime to the leaky mode resonances. By varying the length of the cylindrical rod segment, the continuous transition from a sphere towards an infinite cylindrical nanowire can be traced and addressed This continuous transition is of particular interest as it reveals the direct relationship between the different magnetic and electric modes and their gradual transformation into mixed longitudinal and radial cavity modes. Several features of the intermediate regime are identified, which are not present in either the spherical or infinite cylindrical case These hybrid resonances of dielectric nanowires may be exploited in the rational design of nanophotonic devices and metasurfaces
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