The uses of solar energy instead of fossil fuels to supply the global energy demand demonstrate the importance of developing solar cells. Among all solar cells, colloidal quantum dot solar cells have attracted particular attention due to their easy fabrication, size control, low cost, and flexibility. The depleted heterostructure solar cell is introduced and simulated using quantum dots of CdS and TiO₂ layers. Then, the Schrödinger equation is solved in the spherical polar coordinate and using the obtained eigenfunctions and eigenvalues, the absorption coefficient of other structural parameters are obtained by finite-difference time-domain method. Then solving Maxwell and Poisson equations using the electric field emitted from sunlight radiation, the generation rates of carriers and the current density and other characteristics of the solar cell based on introduced structure are obtained. For studied structures, the obtained optimum results are J_sc  ≈  15  mA  /  cm² and η  ≈  7  %  . The obtained values are relatively good in comparison with the experimental results for similar materials.

The absorption enhancement in the graphene monolayer for the terahertz frequency is investigated. This is achieved by placing the graphene monolayer on a dielectric grating backed with a reduced Bragg grating and a metallic mirror. Complete absorption is achieved at resonance and the absorption spectra exhibit an ultranarrow shape, which is attributed to the combined effects of the guided mode resonance with dielectric grating and the photonic bandgap with Bragg grating. Moreover, the designed graphene absorber possesses antenna-like response and thus can be used as a thermal emitter with high directionality. To disclose the physical origins of such absorption effects, the electric-field intensity distributions are investigated. Furthermore, the peak position of the absorption spectra can be tuned by only a change in the Fermi level. Our results may potentially be used for developing the next-generation graphene-based optoelectronic devices.

Optical properties of 3.8-nm CuInS₂  /  ZnS core/shell quantum dot-doped optical fiber (CIS/ZnS QD-doped OF) were theoretically investigated as a function of fiber length, doping concentration, and pump power. The two-energy level system-based rate equations and power propagation equations were used to calculate the emission properties of QDs doped in the fiber. The emission spectra of CIS/ZnS QD-doped OF showed higher stability than the performance of the control sample doped with PbSe QDs under the same calculation parameters, which was confirmed by the smaller redshift rate as the fiber length increased. In addition, the maximal emission intensity of CIS/ZnS QD-doped OF was about five times that of PbSe QD-doped OF. Further, the light emitted by CIS/ZnS QDs could propagate in the fiber core for long distance with less reabsorption. The theoretical calculations fitted well with the experimental data in the literature. We provide a theoretical basis for CIS/ZnS QDs to be used as OF dopants to improve the fiber emission.

The quantum theory of multiphoton-stimulated bremsstrahlung of charged carriers on an arbitrary electrostatic potential of impurity ion in doped bilayer graphene (BG) in the presence of coherent electromagnetic radiation is developed. A pump wave field is considered exactly, while the electrostatic potential of doped ions is considered a perturbation. The essentially nonlinear response of BG to a pump wave and the significant differences from the case of single-layer graphene, which can be associated with nonlinear parabolic dispersion, are shown. The latter opens a new way to manipulate the electronic transport properties of conductive electrons of BG by a coherent radiation field in the “domain from the terahertz to mid-infrared frequencies.”

Photonic crystal (PhC) structures with appropriate characteristics are necessary to control spontaneous emission from fluorophores while designing miniaturized lasers. We report the fabrication and detailed studies on the emission features of two different spectrally engineered PhC heterostructures made from dye-doped opal and one-dimensional (1-D) multilayer stack. Our results demonstrate notable enhancements of emission from PhC heterostructure enabled by the stopband overlap of three-dimensional (3-D) opals and 1-D multilayers. In the presence of the 1-D multilayer, the distributed feedback from opals further enhances the emission from the dye. We emphasize the role of the interplay of the spectral overlap of stopbands and the band edges in the dye-doped PhC heterostructures to control their emission features. The emission results obtained from our heterostructures are very much dependent on the relative spectral position of the stopbands of the constituent 1-D and 3-D photonic crystals. Input pump energy-dependent emission results indicate that such heterostructures are potential candidates for designing colloidal PhC-based lasers.

We theoretically expanded the capabilities of optical sensing based on surface plasmon resonance in a prism-coupled configuration by incorporating artificial neural networks (ANNs). We used calculations modeling an index-matched substrate with a metal thin film and a porous chiral sculptured thin film (CSTF) deposited successively on it that is affixed to the base of a triangular prism. When a fluid is brought in contact with the exposed face of the CSTF, the latter is infiltrated. As a result of infiltration, the traversal of light entering one slanted face of the prism and exiting the other slanted face of the prism is affected. We trained two ANNs with differing structures using reflectance data generated from simulations to predict the refractive index of the infiltrant fluid. The best predictions were a result of training the ANN with the simpler structure. With realistic simulated-noise, the performance of this ANN is robust.

For diffusion-limited nBn detectors, using an absorption layer much thinner than the optical attenuation length and minority carrier diffusion length can improve the dark current to provide greater sensitivity or higher temperature operation. However, if the quantum efficiency (QE) also decreases with absorber thickness, the advantage of reduced dark current is eliminated. We discuss the use of a metallic grating to couple the incident light into laterally propagating surface plasmon polariton (SPP) modes and increase the effective absorption length. We fabricate the gratings using a deposited Ge layer, which provides a uniform profile without increasing the dark current. Using this process in conjunction with a 0.5-μm-thick InAsSb absorber lattice-matched to GaSb, we demonstrate an external QE of 34% for T  =  78 to 240 K. An nBn structure with an InAs_0.8Sb_0.2 absorber that is grown metamorphically on GaSb using a step-graded InGaSb buffer has a peak external QE of 39% at 100 K, which decreases to 32% by 240 K. Finally, we demonstrate that a grating with SPP resonance near the bandgap extends the absorption band and can potentially reduce the dark current by another factor of 3 to 8 times in addition to the 5  ×   reduction due to the thinner absorber.

The microscopic quantum theory of nonlinear stimulated scattering of chiral particles in doped AB-stacked bilayer graphene on the Coulomb field of charged impurities in the presence of coherent electromagnetic radiation is presented. The Liouville–von Neumann equation for the density matrix is solved analytically. Here, the interaction of electrons with the scattering potential is taken into account as a perturbation. The absorption rate of nonlinear inverse-bremsstrahlung for a grand canonical ensemble of fermionic chiral particles is calculated using the obtained solution. The analysis of the obtained rate shows that from terahertz to the midinfrared range of frequencies there is significant absorption of incident radiation via multiphoton-stimulated bremsstrahlung mechanism.

We introduce phase-change material Ge₂Sb₂Te₅ (GST) into metal–insulator–metal (MIM) waveguide systems to realize chipscale plasmonic modulators and switches in the telecommunication band. Benefitting from the high contrast of optical properties between amorphous and crystalline GST, the three proposed structures can act as reconfigurable and nonvolatile modulators and switches with excellent modulation depth 14 dB and fast response time in subnanosecond while possessing small footprints, simple frameworks, and easy fabrication. We provide solutions to design active devices in MIM waveguide systems and can find potential applications in more compact all-optical circuits for information processing and storage.

In order to improve the traditional gallium nitride (GaN)-light-emitting diode (LED) luminous efficiency, a structure of the GaN-LED is designed based on the local field enhancement of surface plasmon (SP). The principle of improving LED luminous properties using the SP features is described in detail. The factors that affect the light extraction efficiency of this LED structure are simulated with the COMSOL software. The thickness of p-GaN layer, the thickness of indium tin oxide (ITO) layer, the grating period T, the duty ratio r, as well as the shape of the interface between p-GaN and ITO are studied. The normalized radiated powers, the normalized absorbed powers, and the electric field distribution of this structure under different structure parameters have been achieved. The results show that when the thickness of p-GaN layer is 110 nm, the thickness of ITO buffer layer is 120 nm, the period T is 370 nm, the duty ratio is 0.5, and the value of D₁  /  T is 0.6. The luminous intensity of LED is higher than that of the traditional LED nearly 43 times and is nearly 36 times higher than that of the Ag nanosphere structure, and SPs can be coupled with the active layer effectively to improve the luminous efficiency of LED, providing a theoretical guide for the preparation of high-performance GaN-LED chips.

The luminescence emission of graphene quantum dots (GQDs) is around the visible range, so it could be used as light-emitting diodes or biological markers. Also, the diameter of the GQDs determines the luminescence emission by the variation of the energy gap. For this reason, it is important to establish models that help us to estimate the size of the GQDs. In particular, the radial breathing mode (RBM) allows the correlation of the diameter in some nanostructures with a specific vibrational frequency that could be obtained by Raman spectroscopy. For this reason, we performed the calculation of the RBM in GQDs using the density functional theory. We performed the calculations with different exchange and correlation (XC) functionals to compare the values obtained and select which XC functional could be more accurate in the calculation of the RBM. Also, we found that in the case of the energy gap the values obtained from the various functionals are very similar for standard XC functionals. By contrast, the RBM within the local density approximation is very similar to the other XC functionals, but with small differences to that obtained within the generalized gradient approximation (GGA) to the XC functional. Finally, we found that the dependency of the RBM behavior on the diameter could be described by the inverse of its radius as in the case of nanowires.

CMOS circuits face several limitations due to the rise in leakage current at extreme nanometer levels. It has made the industry to find suitable alternatives to meet the standards set by Moore’s law. Quantum-dot cellular automata is an emerging paradigm with the potential to replace CMOS circuits at extreme nanoscale levels. Adders are integral part in almost every digital system. In this work, a novel cost-efficient full adder is proposed. The proposed full adder has the least cost, delay, and 66% reduction in the number of wire crossings, compared to existing state-of-the-art designs. The proposed design has 40% lesser cost, compared to the existing design. The proposed adder can be extended to implement any kind of N-bit adder. The proposed full adder can be implemented as a half adder without any wire crossing and additional cells. The proposed designs are evaluated and verified using QCADesigner.

A highly birefringent polarization-maintaining dual-core photonic crystal fiber (DC-PCF) structure with elliptical air holes around the cores has been designed for possible supercontinuum generation over two octaves spanning a spectral bandwidth in the 400- to 1800-nm wavelength range. The supercontinuum (SC) spectrum covers the near-UV, visual, and near-infrared regions of electromagnetic spectra when a hyperbolic secant pulse of 50 fs duration, 322 mW average power, and 80 MHz repetition rate corresponding to 4.03 nJ energy is launched into the DC-PCF around a 1060-nm pumping wavelength. The generated SC spectrum satisfies the necessary requirements for applications in biophotonics, telecommunications, and frequency metrology.

We present the study and design of an optical switch based on a hybrid plasmonic-vanadium dioxide-based waveguide. The power-attenuating mechanism takes advantage of the phase change properties of vanadium dioxide that exhibits a change in the real and complex refractive indices upon switching from the dielectric phase to the metallic phase. The proposed switch was designed to operate under the telecommunication wavelength. The switch was analyzed by three-dimensional full electro-magnetic simulations. An ER per unit length of 4.32  dB  /  μm and IL per unit length of 0.88  dB  /  μm are realized for the proposed electro-optical switch. The proposed electro-optical switch has the advantages of small device foot-print, compatible with the existing VLSI-CMOS technology and broadband operation.