Abstract
We propose an all-silicon-based nano-antenna that functions as not only a wavelength demultiplexer but also a polarization one. The nano-antenna is composed of two silicon cuboids with the same length and height but with different widths. The asymmetric structure of the nano-antenna with respect to the electric field of the incident light induced an electric dipole component in the propagation direction of the incident light. The interference between this electric dipole and the magnetic dipole induced by the magnetic field parallel to the long side of the cuboids is exploited to manipulate the radiation direction of the nano-antenna. The radiation direction of the nano-antenna at a certain wavelength depends strongly on the phase difference between the electric and magnetic dipoles interacting coherently, offering us the opportunity to realize wavelength demultiplexing. By varying the polarization of the incident light, the interference of the magnetic dipole induced by the asymmetry of the nano-antenna and the electric dipole induced by the electric field parallel to the long side of the cuboids can also be used to realize polarization demultiplexing in a certain wavelength range. More interestingly, the interference between the dipole and quadrupole modes of the nano-antenna can be utilized to shape the radiation directivity of the nano-antenna. We demonstrate numerically that radiation with adjustable direction and high directivity can be realized in such a nano-antenna which is compatible with the current fabrication technology of silicon chips.
Highlights
It is well known that the operating frequency of an antenna depends strongly on the dimension of the antenna
The radiation pattern of a nano-antenna is determined by the interference between the moments obtained from the multipole expansion in a Cartesian coordinate or the interference between the coefficients obtained from the multipole expansion in a spherical coordinate
It can be seen that the backward scattering increases with increasing phase difference and it becomes equal to the forward scattering when the phase difference is increased to π/2
Summary
It is well known that the operating frequency of an antenna depends strongly on the dimension of the antenna. For dielectric and semiconductor nanoparticles, it has been demonstrated that the constructive interference between the induced electric and magnetic dipole (ED and MD) may lead to the enhanced scattering in the forward direction and suppressed scattering in the backward direction at the wavelength where the first Kerker’s condition is satisfied [27,28]. The situation is reversed at the wavelength where the second Kerker’s condition is satisfied This kind of directional scattering is quite useful in the design of all-dielectric nano-antennas. An effective way to control the radiation direction of a nano-antenna relies on the interference of electric and magnetic modes of different orders, leading to the so-called side scattering. Electric and magnetic modes of different orders can be readily excited in dielectric nanostructures, offering more possibilities to engineer the radiation direction and directivity of a nano-antenna.
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