We report Purcell factor enhancement in Silicon dimer in the visible region. Dimer of Silicon spheres having diameter 130 nm has the electric field enhancement at the wavelength of 620 nm. Point electric dipole has been placed between the Silicon dimer to calculate the Purcell factor. Purcell factor or spontaneous emission rate depends on quality factor Q and mode volume V by the relation Q/V. For high Purcell factor, quality factor should be high and mode volume should be small. But high quality factor has the disadvantage that light matter interaction takes place over a very narrow bandwidth. So that coupling of emitters with cavities is very weak. Another way of increasing Purcell factor is to decrease mode volume. In our design, quality factor is 50 which is not so high but mode volume is very small of the order of 10-4 μm3 , which results in very high Purcell factor of 2400. Enhancement of Purcell factor takes place due to high local density of states. In this type of dielectric nanoparticles, electric field enhancement takes place due to Mie resonance. In single dielectric nanoparticle, electric and magnetic field confine in the nanoparticle at the wavelengths of resonance. But, in the dielectric dimer, electric field confinement between the two nanoparticles results in high Purcell factor. High Purcell factor in dielectric nanoparticles leads to many applications in nanoantennas and lasers.
All-dielectric nanoparticles have attained a lot of attention owing to the lesser loss and better quality than their metallic
counterparts. As a result, they perceive applications in the field of nanoantennas, photovoltaics and nanolasers. In the
dielectric nanoparticles, the electric and magnetic dipoles are created in dielectric nanoparticles when they interact with
the light of a particular frequency. Kerker’s type scattering is obtained where electric and magnetic dipoles interfere. In
our design, Silicon cylindrical nanoparticles having radius of 70 nm and length 120 nm have been considered. The
propagation of light is taken along the length of the cylinder. The scattering cross section has been obtained and plotted
with respect to the wavelength. At the peaks of scattering spectra, electric and magnetic dipoles are created at the
wavelengths of 510 nm and 600 nm, respectively. Both dipoles interfere at the wavelengths of 550 nm and 645 nm. At
these wavelengths, far field scattering pattern has been calculated. At the wavelength 645 nm, forward scattering takes
place because electric and magnetic dipoles are in phase at this wavelength. Further, directivity is enhanced by taking the
planar array of the nanoparticles. It has been observed that directivity increases by increasing the size of the array. Also,
there is an increase in the directivity by increasing the gap between the nanoparticles. This enhancement of directivity
can lead to the design of all dielectric cylindrical nanoantennas.
In this paper we present the design of a metamaterial perfect absorber (MPA) made up of an array of dielectric microcubes grown on a metallic substrate. The fundamental principle of operation of the proposed structure is Mie Resonance occurring in high permittivity particles in combination with the negative permittivity provided by the metallic substrate. The proposed structure is simpler than all other existing metamaterial perfect absorber structures. The geometrical parameters of the structure are between 1 μm and 10 μm, hence it is not supposed to pose any challenge during fabrication. Moreover, the structure has been designed for terahertz spectrum which is the most unexplored part of the spectrum.
We theoretically demonstrate ultradirectional, azimuthally symmetric forward scattering by dielectric cylindrical nanoantennas for futuristic nanophotonic applications in visible and near-infrared regions. Electric and magnetic dipoles have been optically induced in the nanocylinders at the resonant wavelengths. The cylindrical dielectric nanoparticles exhibit complete suppression of backward scattering and improved forward scattering at first generalized Kerker’s condition. The influence of gap between nanocylinder elements on the scattering pattern of the homodimers has been demonstrated. Further, for highly directive applications, a linear chain of ultradirectional cylindrical nanoantenna array has been proposed.
A tunable cylindrical all dielectric optical nanoantenna has been proposed. A silicon nanocylinder of radius 60 nm and
height 150 nm has been considered. The azimuthally symmetric, complete forward scattering at first Kerker’s condition
and backward scattering with minimum forward scattering at second generalized Kerker’s condition in near infra-red
region has been observed for the proposed design which makes silicon nanocylinder a promising candidate for optical
nanoantenna applications. The effect of the dimensions of the dielectric nanocylinder on the scattering properties of the
cylindrical nanoantenna has been analyzed using finite element method. We have analyzed that the variation in diameter
of nanocylinder has great influence on the strength of interference of electric and magnetic dipolar resonances. Further,
we have observed tuning ability of the cylindrical nanoantenna with respect to the variation in its radius.
In this paper, electric and magnetic resonances induced in the ellipsoidal dielectric nanoparticles in the optical range have been analyzed. Circular displacement currents excited inside the elliptical nano-particles by the incident light result in magnetic dipolar resonance in the dielectric nanoparticles. Kerker’s type scattering is observed due to the mutual interference of electric and magnetic resonances. The effect on the resonance conditions with the variation in the relative permittivity from Er= 5 to Er= 20 of the ellipsoidal nanoparticle has been observed. It has been analyzed that peaks of electric and magnetic resonances come closer by decreasing the electric permittivity of the nanoparticle, which leads to the increase in the directionality in the forward direction, as verified using Generalized Kerker’s condition. Further, far field scattering patterns have been obtained using the finite element method. Here, the electric and magnetic resonances have been optically induced up to quadrupolar modes. There is enhancement of the directionality in the forward direction when electric and magnetic resonances are in phase. Further, the effect of size of the linear array of ellipsoidal nanoparticles on the directionality has been analyzed. It has been observed that there is increase in the directivity by increasing the chain of the nanoparticles. Thus, the ellipsoidal nanoparticles can lead to the design of low loss and highly directional optical nanoantennas.
Mie resonance in square arrays of dielectric rods has been reported. Arrays in square lattice of dielectric rods with very high permittivity in air have been considered. Light of transverse electric mode has been launched on the square array of cylindrical dielectric rods. Mie resonance of first two orders has been observed in the dielectric rods, due to which electric and magnetic dipoles are generated in the rods. Thus, electric resonance and magnetic resonance at different frequencies has been observed with material of high value of permittivity.
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