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.
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.
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.
We numerically report a design of a highly nonlinear spiral-shaped photonic crystal fiber (PCF) in Ga8Sb32S60 chalcogenide glass for nonlinear applications in mid-infrared region. We have tailored the structural parameters to obtain all-normal and nearly zero flat-top dispersion profile. A flat-top dispersion curve is obtained with a negative dispersion value of -98.63 ps.nm-1 km-1 . This structure possesses a very high nonlinear coefficient of 49190 W-1 km -1 with effective mode area of the propagating fundamental mode as 0.833 μm2 at a pump wavelength of 1.9 μm. This highly nonlinear spiral-shaped PCF is suitable for the generation of an ultra-broadband supercontinuum spectrum in mid-IR domain. Various nonlinear applications of supercontinuum generation are pump-probe spectroscopy, nonlinear microscopy, metrology, frequency combs generation and optical coherence tomography.
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, 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..
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.
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.
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.
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.
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.
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 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.
In this paper, enhanced image resolution by modification in the two dimensional (2-D) photonic crystal structures has
been proposed. The equal frequency contour (EFC) analysis have been done using plane wave expansion method which
shows that the structure exhibits an effective isotropic refractive index, neff = -1 at a normalized frequency of ω =
0.2908(2πc/a) for TM polarization, located near the second band. At ω = 0.2908(2πc/a) for TM polarization, the
considered PhC structure behaves as a superlens, as analyzed using the finite difference time domain (FDTD) method.
The image resolution and stability of the photonic crystal slab lens has been enhanced by creating disorder in the top and
bottom layer of the PhC structure. The intensity field distributions of the optimized structure exhibit the enhanced image
quality with full width at half maximum (FWHM) of 0.311 λ. The proposed structure can also be used to sense the
different type of blood constituents.
Propagation characteristics of a cladding doped defect-core large mode area W-type photonic crystal fiber have been
investigated by using finite element method. In the proposed structure the central air hole has been removed to form the
defect core and the second layer of cladding rings around the central core have been selectively doped with different
concentration of fluorine to tune the refractive index of the doped silica rods. The bend loss, dispersion, effect of bending
on dispersion, and nonlinear coefficient of the proposed photonic crystal fiber design has been numerically investigated.
The proposed W-type photonic crystal fiber has low bend loss, low dispersion, large-mode-area with low value of
nonlinear coefficient at wavelength of 1.55μm. The structure can be utilized for telecommunication applications, for
applications in high power fiber lasers, amplifiers and sensors.
In this paper, we have proposed the design of all-optical AND logic gate using the combination of universal
NAND gates. The structure consists of hexagonal arrangement of air holes in silicon. The proposed structure has
been designed using the finite difference time domain (FDTD) method. The optimized NAND gates have been
arranged in a combination such that the combined structure behaves as an all-optical AND logic gate. The
proposed structure exhibits a response period of 6.48ps and bit rate of 0.154 Tb/sec.
We propose a design for a polarization beam splitter based on the phenomenon of a photonic crystal directional coupler. The design consists of a honeycomb lattice arrangement of air holes of different radii in a silicon-on-insulator substrate exhibiting a complete photonic bandgap. The results obtained by the finite-difference time domain method show that the extinction ratio for transverse electric (TE) and transverse magnetic (TM) polarizations is 24.56 and 28.29 dB, respectively, at a wavelength of 1.55 μm. The degree of polarization for TE polarization is 99.29% and for TM polarization is 99.70%. Hence, the proposed design can be efficiently used as a polarization splitter for on-chip integrated devices.
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.
In this paper, we have proposed a design for slow light effect in pinch photonic crystal waveguide. The design consists of two dimensional triangular arrangements of air holes in silicon on insulator substrate. From the calculations it has been found out that for the proposed structure the group index is high and group velocity dispersion is low. The confinement of light in the pinch waveguide with slow light effect can be a strong candidate for sensor applications.
We have proposed a design for slow light with ultraflat dispersion in a slotted photonic crystal waveguide consisting of a hexagonal arrangement of elliptical air holes on a silicon-on-insulator substrate. The proposed structure has low group velocity and low group velocity dispersion with a wide normalized bandwidth range of 0.0089. The proposed structure can be used as an optical buffer for the storage of a large amount of data due to the large value of the normalized delay bandwidth product equal to 0.634. An optimized structure for a slotted photonic crystal has been analyzed for its applications as both a time and wavelength division demultiplexer. Furthermore, the time delay between two adjacent wavelengths (1550 and 1555 nm) is more than that reported earlier.
Photonic crystal based nano -displacement sensor for horizontal as well as vertical displacement has been proposed. The
design is highly sensitive in the displacement region 40nm–120nm with sensitivity 0.00461nm-1 for horizontal
displacement of the moving PhC waveguide. For vertical displacement of the moving PhC waveguide the design is
highly sensitive in the region 150nm-200nm with sensitivity 0.00684nm-1 for zero horizontal displacement, 130nm-
200nm with sensitivity 0.00523 nm-1for 10nm horizontal displacement, 130nm-200nm with sensitivity 0.00418 nm-1 for 20nm horizontal displacement, 130nm-200nm with sensitivity 0.00461 nm-1for 30nm horizontal displacement,100nm-130nm with sensitivity 0.00466 nm-1for 40nm horizontal displacement. It has been concluded that the proposed design behaves as a Nano-displacement sensor for horizontal displacement of the moving PhC waveguide up to the region of displacement of magnitude of 400nm and for vertical displacement of the moving PhC waveguide up to the region of
displacement of magnitude of 300nm.The proposed design can behave as a nano-Displacement sensor for both horizontal
as well as vertical displacement.
Photonic crystals (PhCs) have emerged as one of the most significant topics in the field of optical communication since their first introduction by Yablonvitch 1 and John 2. Recently, interest has been grown in the design and development of optical logic gates based on different schemes 3-10. In this paper, we report the design of optical logic AND gate based on two structures, one of which is a hexagonal lattice with silicon (Si) rods in air (SRA) and another is the hexagonal lattice arrangement of air holes in silicon (AHS) with air waveguides. Both the gate structures are based on Y shaped PhC waveguides and analyzed by plane wave expansion (PWE) method. The simulation results show that the proposed structures operates as an AND gates and has a bit rate of 2.016Tbit/s for SRA and 1.785Tbit/s for AHS structure. By appropriately choosing the size and the interaction length of the central rod in SRA and size of central hole in AHS, the optimal performance of the proposed AND logic gates has been achieved.
We explore the application of photonic band gaps (PBGs) in photonic crystal structures to propose the design of an ultracompact PBG polarizer. The existence of complete PBGs in certain photonic crystal structures and the variation introduced in the PBGs by the creation of defects has been utilized to design a PBG polarizer at 1.55 µm with a degree of polarization equal to 1 leading to the formation of a super polarizer.
Certain select structures in photonic crystals (PhCs) exhibit complete photonic band gap i.e. a frequency region where the photonic band gaps for both polarizations (i.e. transverse electric and transverse magnetic modes) exist and overlap. One of the most fundamental applications of the photonic band gap structures is the design of photonic crystal waveguides, which can be made by inserting linear defects in the photonic crystal structures. By setting closely two parallel 2D PhC waveguides, a directional waveguide coupler can be designed, which can be used to design a polarization splitter. In this paper we design a polarization splitter in a photonic crystal structure composed of two dimensional honeycomb pattern of dielectric rods in air. This photonic crystal structure exhibits a complete photonic band gap that extends from λ = 1.49 μm to λ = 1.61 μm, where lambda is the wavelength in free space, providing a large bandwidth of 120 nm.
A polarization splitter can be made by designing a polarization selective coupler. The coupling lengths at various wavelengths for both polarizations have been calculated using the Finite Difference Time Domain method. It has been shown that the coupling length, for TE polarization is much smaller as compared to that for the TM polarization. This principle is used to design a polarization splitter of length 32 μm at λ = 1.55 μm. Further, the spectral response of the extinction ratios for both polarizations in the two waveguides at propagation distance of 32 μm has been studied.