  Near- and far-field optical properties of silicon nanostructures under linear
polarization (Gaussian beam), and azimuthally or radially focused cylindrical
vector beams are investigated by finite-difference time-domain method (FDTD) in
Meep open-source software. A python toolkit allowing FDTD simulations in Meep
for using those excitation sources is provided. In addition to the preferential
excitation of specific electric or magnetic resonance modes as function of the
excitation beam polarization, it is shown in the case of spheroids that shape
anisotropy affects the resonance wavelength and the dipole orientation of the
magnetic or electric dipole mode. For radial or linear polarization, the
electric dipole resonance is split by an anapole mode depending on the spheroid
symmetry axis with respect to the electric field orientation. Finally, the
optical properties in both far-field (scattering pattern) and near-field
(electric and magnetic field hot spots) can be tuned by changing the excitation
polarization at a fixed wavelength and selecting properly the spheroid shape
and dimensions. These numerical simulations can be extended to more complex
shapes, or fabrication-friendly nanostructures such as nanocylinders with
circular or elliptic sections.
