Nishant Shankhwar

Design and analysis of a hollow bowtie nanoantenna

In this paper, a pair of hollow bow-tie nanoantenna with a feed gap has been designed using gold in the visible frequency range. This nanoantenna exhibits a strong field enhancement in the feed gap region at the resonance wavelength due to the localized surface plasmon. The absorption cross-section of this nanoantenna has been compared with the solid bowtie nanoantenna and it has been observed that the absorption cross section in hollow bowtie nanoantenna is less as compared to solid bowtie nanoantenna. This is because of the less volume availability for light absorption in the hollow bowtie nanoantenna. So, the main reason of using a hollow bowtie over a solid bowtie is the reduced absorption cross-section. Further, properties of hollow bowtie nanoantenna have been enhanced by geometric optimization using COMSOL Multiphysics software.

Dielectric zero-index metamaterial filled photonic crystal defect waveguide: design and analysis

In this work, a novel design of dielectric zero-index metamaterial (ZIM) filled photonic crystal defect waveguides have been proposed. The ZIM used here is basically a photonic crystal having Dirac cone at gamma point of the band structure. Existence of Dirac cone implies the linear dispersion in the vicinity of the Dirac point which is the main reason behind the zero-index behaviour. It has been shown in this article, that when such metamaterial is inserted inside a photonic crystal defect waveguide it reduces the effect of bending on transmission coefficient as compared to the conventional designs. The proposed design comprises of square arrays of Si rods in air, in which, the periodicity to wavelength ratio (a/λ) for ZIM and the surrounding photonic bandgap (PBG) structure are 0.541 and 0.35 respectively. Wavelength of operation is 1550 nm. Furthermore, as the ZIM is made up dielectric only, its free from ohmic losses.

Plasmonic waveguides based optical AND gate

In this paper, a design of Plasmonic waveguides based optical AND gate has been proposed. Various designs of Photonic crystal based optical logic gates have already been envisioned and proposed during the past decade, in which, wavelength of operation is comparable to the geometrical parameters. On the contrary, the proposed structure consists of Plasmonic waveguides whose thickness is much smaller than the wavelength of operation. Plasmonics can pave way for the development of optical interconnects that are small enough to operate in nanoscale devices. Nowadays, Plasmonics is being implemented in a large number of areas, one of which is confinement of optical power in subwavelength devices. This may pave the way for large scale on-chip integration for the development of all optical circuits for optical computing systems. Moreover, the proposed design is simple and easy to fabricate using techniques like thin-film technology and lithography. This AND gate has been designed and analysed using the Finite Element Method (FEM) software. The proposed structure has been made by using silver material as a waveguide and silicon as the surrounding dielectric..

All-dielectric cylindrical nanoantennas in the visible range

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.

Design and analysis of tip slotted square patch nano-antenna

In this paper, study of novel design of gold tip slotted square patch nanoantenna placed over silica substrate has been done. Designed antenna is optimised on basis of various geometrical parameters such as antenna length, thickness, gap between the antenna etc. using COMSOL Multiphysics a finite element method (FEM) based simulation software for the near field analysis. Both single and coupled tip slotted square patch antenna are analysed and the effect of slot on the antenna performance is also studied. The operational wavelength is in the near and mid infrared range of the electromagnetic (EM) spectrum as nanoantenna finds various applications in the field of near field microscopy, spectroscopy, infrared(IR) detection, waste energy and solar energy harvesting.

LiTaO3 microcubes based metamaterial perfect absorber

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.

Split-nanotube-based negative index metamaterial for midinfrared wavelengths

Abstract. A design of split-nanotube-based negative index metamaterial for the infrared spectrum has been proposed. The proposed design and its operation are similar to that of a split-ring resonator (SRR) without inheriting the fabrication difficulties associated with conventional SRR. A negative refractive index has been achieved using a split-nanotube in combination with a periodic array of metallic wires between 1.5 and 3.3  μm.

Controlling the evanescent waves using metamaterials

In this paper we discuss the role of evanescent waves in nanophotonic devices, especially in metamaterials. We discuss how metamaterial cladding increases the power confinement in waveguides by increasing the momentum of evanescent waves. The momentum of evanescent waves is controlled in such a fashion that condition of total internal reflection is not disturbed. This becomes possible by making the cladding anisotropic. Anisotropic cladding gives the facility to control the parallel and perpendicular components of wave vector individually. We analyze the efficiency of this technique in case of waveguides. We have also discussed the advantages of collecting evanescent waves for imaging sub wavelength objects.

Magnetic response of split nanotube type metamaterial at near infrared frequency

In this paper, we present the design of a split nanotube type metamaterial which shows strong magnetic resonance at infrared frequency. Its operation is similar to that of split ring resonator (SRR) but is easier to fabricate at nanoscale.

Design and analysis of near perfect metamaterial reflector in visible range

Cone shaped resonators have been proposed to create a near perfect metamaterial reflector in the visible range (640nm-680nm). Resonators are made up of high permittivity dielectric (Si). In the considered wavelength range reflectance is above 90% with maximum value of 99.5% at 660nm. It is Mie-Resonance based structure showing magnetic and electric resonance at different wavelengths.