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Our latest study builds upon our previous research on multi-wall carbon nanotubes (MWCNTs) by exploring the photonic responses of regularly β-aligned arrays of these nanotubes. Through extensive calculations using the Finite Difference Time Domain Method, we determined that MWCNT-based photonic crystals possess significant Bragg reflections of up to 80% without experiencing substantial attenuation, even at wavelengths as low as 17 nm. This discovery is of great significance, as traditional materials have not been able to scatter UV photons within this frequency range efficiently. Following extensive research, we analyzed various model parameters such as lattice periodicity, inner and outer radii of MWCNTs, and the polarization (TM or TE) and direction (Γ-X or Γ-M) of the incident wave. Our findings present promising implications for advancing ultra-highfrequency photon manipulation in EUV applications, with potential developments ranging from UV laser mirrors to EUV lithography lenses, and beyond to UV spectroscopy collimators. [ABSTRACT FROM AUTHOR]

We present a computational study on the electrical behavior of the field-effect transistor based on vertical graphene-hBN- χ 3 borophene heterostructure and vertical graphene nanoribbon-hBN- χ 3 borophene nanoribbon heterostructure. We use nonequilibrium the Green function formalism along with an atomistic tight-binding (TB) model. The TB parameters are calculated by fitting tight-binding band structure and first-principle results. Also, electrical characteristics of the device, such as ION/IOFF ratio, subthreshold swing, and intrinsic gate-delay time, are investigated. We show that the increase of the hBN layer number decreases subthreshold swing and degrades the intrinsic gate-delay time. The device allows current modulation 177 at room temperature for a 1.2 V gate-source bias voltage. [ABSTRACT FROM AUTHOR]

We present the results of a numerical study on the characteristics of MoS2-based field-effect photodetectors (FEPhDs). These FEPhDs consist of 12-nm-long and 1.42-nm (1.45-nm)-wide MoS2 armchair (zigzag)-nanoribbons (MoS2-A(Z)NRs), acting as channels connected to two semi-infinite graphene electrodes, serving as source and drain terminals to minimize the terminals' series resistances. The simulation method used here is the nonequilibrium Green's function formalism plus an atomistic tight-binding (TB) model. We employed the TB model to obtain characteristics like the density of states versus electron energy, current–voltage curve, and photocurrent versus photon wavelength (λ). For the latter, we consider illuminating the A(Z)NR channels with a broadband optical signal covering the λ = 330–830 nm range. Our simulations show that passivation of ANR edges with H2 and OH molecules reduces the semiconducting bandgap by ~ 28% (for H-ANR) and ~ 28.6% (for OH-ANR). The numerical results show that, among the three ANR channels, the optimum photoresponsivity of Rph ≈ 43.88 mA μW−1 belongs to the FEPhD with the MoS2-OH-ANR channel biased at VDS = 200 mV and VGS = 0, at λ ≈ 451 nm, independent of the illumination intensity. Among the three ZNR channels, the best photoresponsivity of Rph ~ 27.02 mA μW−1 belongs to the unpassivated channel under the same biasing condition but at λ ≈ 477 nm. The results also show that the optimum biasing condition differs from one FEPhD to another. The results show that the proposed MoS2-A(Z)NR-based FEPhDs can be promising candidates for nanoscale optoelectronic devices in the UV–Vis range. [ABSTRACT FROM AUTHOR]

We present a tight-binding (TB) model for describing the electronic properties of the free-standing χ3 and β12 borophenes via the Slater–Koster approach. This model is constructed through s, px, py, and pz orbitals for each boron atom. The optimal Hamiltonian plus the overlap matrix are calculated by fitting the results of the TB model and density functional theory calculations using the least-squares method and the Levenberg–Marquardt nonlinear fitting algorithm. Considering three nearest-neighbors and a non-orthogonal basis set, this TB model accurately describes energy bands around high-symmetry k-points. [ABSTRACT FROM AUTHOR]

We have obtained a simple numerical model that explains the temperature behavior of multi-quantum-dot (QD) nanophotonic devices whose operations are based on optical near-field (ONF) interactions between any two resonant QDs that are in thermal equilibrium. This model involves a set of coupled rate equations that govern the temporal behavior of the QDs' energy level occupancies. Under a certain operating condition, this simple model can substitute for the more complex density matrix (DM) approach in modeling the temperature dependence of the ONF energy transfer rate ([R.sub.ONF]) between any two resonant QDs in thermal equilibrium. The same applies for modeling the system state-filling time ([[tau].sub.S]). Applying our simple model to a two-QD system, we have derived analytical formulas for the interdot and the intradot transfer rates at finite temperatures (T [greater than or equal to] 0). Furthermore, by assuming a unidirectional energy transport operating condition, we have also derived an analytic formula for calculating [[tau].sub.S] for a two-QD system. To the best of our knowledge, this work is the first instance of reporting such analytic equations. Approximated values of [[tau].sub.S] obtained from our simple analytic equation are in reasonable agreements with those calculated by the DM approach. [c] 2010 Optical Society of America OCIS codes: 350.4238, 230.5590.

We propose a new numerical model to analyze heat induced by two-photon absorption and free-carrier absorption, while high intensity optical pulses propagate along silicon-on-insulator (SOI) nanowave-guides (NWGs). Using this model, we demonstrate that such induced heat causes a shift in the amount of wavelength conversion and hence deteriorates the converter output characteristics for pulses in the picosecond regime. The wavelength shift induced by a pulse with maximum input intensity and full width at half-maximum of [I.sub.max] = 1.5 X [10.sup.10] W.[cm.sup.-2] and [T.sub.FWHM] = 30 ps, propagating along a SOI NWG with an effective cross-sectional area of [a.sub.eff] = 0.15 [micro][m.sup.2], is shown to be [DELTA][[lambda].sub.s] = 8 pm. We also demonstrate that such a shift can be compensated by tuning the pump intensity down by approximately 6.33%. OCIS codes: 130.4705, 190.3270, 190.4360, 230.7370, 230.7405.

Chromatic dispersion compensation is an essential feature of high speed dense wavelength-division multiplexing (DWDM) systems. We propose a dispersion compensator structure whose characteristics meet the optical DWDM system requirements. The proposed structure is based on Fibonacci quasi-periodic multilayer structures composed of layers with large index differences. Studying the dispersive properties of Fibonacci structures with generation numbers j = 3 and 4, and calculating group delay (GD) and group velocity dispersion (GVD) of their reflection bands, we have demonstrated that to have a smooth GD and almost a constant GVD in each band of a DWDM system, one needs not only to suitably chirp the structure refractive index profile, but also must properly apodize it. We also demonstrate the possibility of achieving high slope GDs and large GVDs by means of high order Fibonacci structures with thicker layers. Finally, by varying the layer dimensions and refractive indices as well as Fibonacci's order, one can design DWDM dispersion compensators suitable for distances as long as 220 km. OCIS codes: 050.1590, 060.4510, 230.2035, 220.1230, 230.4170, 130.2035.

An innovative intensity and phase noise-equivalent circuit model for a multimode semiconductor laser diode is described and discussed.

We synthesized gold nanoparticles at linoleic acid (GNPs@linoleic acid) for glucose sensing application with the help of fluorescence spectroscopy. The synthesis is a non-toxic process. So, the synthesized nanoparticles are safe and biologically compatible with the human body. The synthesis process uses a polyunsaturated fatty acid called linoleic acid that surrounds the GNPs and acts as a reducing and stabilizing agent. In this procedure, first, we achieve the optimal synthesis method by changing the gold salt concentration, which leads to obtaining the maximum sensitivity to changing the glucose concentration. For this purpose, we considered the optimal concentration of gold salt 2 mM. Eventually, gold nanoparticles remain in linoleic acid. In the next stage, we obtain the fluorescence spectra of the synthesized GNPs@linoleic acid (at the excitation wavelength of 405 nm) in the presence of different glucose concentrations. Our measurements show an increase in glucose concentration reduces the peak intensity of the fluorescence for the GNPs@linoleic acid. The main reasons for this reduction are the degradation and auto-oxidation of linoleic acid, catalytic features of GNPs, and the presence of GNPs@linoleic acid in measuring glucose concentrations, enhancing the sensitivity as compared to that of linoleic acid alone by 4.8 times. The synthesized GNPs@linoleic acid can measure the glucose concentration within the linear range of 0–300 mg $\cdot $ dL−1 (i.e., 0-16.65 mM) by a detection limit of 50 mg $\cdot $ dL−1 (~2.8 mM). This measurement range is suitable for clinical applications — i.e., within 70 to 120 mg $\cdot $ dL−1. [ABSTRACT FROM AUTHOR]

We investigate the propagation of a normally incident squeezed coherent state of light through dispersive non-Hermitian optical bilayers, particularly at a frequency that the bilayers hold parity-time (đť'«đť'Ż) symmetry. To check the realization of đť'«đť'Ż-symmetry in quantum optics, we reveal how dispersion and loss/gain-induced noises and thermal effects in such bilayers can affect quantum features of the incident light, such as squeezing and sub-Poissonian statistics. The numerical results show thermally induced noise at room temperature has an insignificant effect on the propagation properties in these non-Hermitian bilayers. Moreover, tuning the bilayers’ loss/gain strength, we show that the transmitted squeezed coherent states through the structure can retain to some extent their nonclassical characteristics, specifically for the frequencies far from the emission frequency of the gain layer. Furthermore, we demonstrate, only below a critical value of gain, quantum optical effective medium theory can correctly predict the propagation of quantized waves in non-Hermitian and đť'«đť'Ż-symmetric bilayers. [ABSTRACT FROM AUTHOR]

Employing the non-equilibrium Green's function with the third order tight binding Hamiltonian, we show that 12.7 nm long and 1.11 nm wide zigzag and armchair graphene nanoribbons (ZGNR and AGNR) in contact with asymmetric source and drain, consisting of graphene topped with Au and Ti, respectively, can operate as visible and solar blind photodetectors under zero externally applied biases. The carbon atoms at the channels' edges are considered to be hydrogen passivated. Numerical simulations show that the unbiased Au-ZGNR-Ti and Au-AGNR-Ti photodetectors can detect photons of energies 2.72 eV (456 nm, visible reign) and 5.02 eV (247 nm, solar blind reign), respectively, with the corresponding quantum efficiencies as high as 90% and 60% and responsivities of 93.8 and 13.4 A/mW. We also show that in Au-ZGNR-Ti the local photocurrents are distributed more around the ZGNR edges in regions near the source and drain sides of the channel, for the zero gate-source voltage (VGS=0), whereas in Au-AGNR-Ti for the same biasing condition, the local photocurrents are distributed far from the AGNR edges within regions near the source and drain sides of the channel. As the applied gate voltage moves away from the Dirac point, the peaks of the local photocurrents move away from the source and drain sides of the channel in opposite directions, in either asymmetric photodetector. Polarities of the local photocurrents are altered, as the gate-source voltage approaches the Dirac point, where the total photocurrent is maximized for both asymmetric photodetectors. [ABSTRACT FROM AUTHOR]

We propose investigating the electro-optical properties of photodetectors based on mono- and bilayer graphene quantum dots or nanodots (GNDs). These photodetectors consist of dissimilar metals (gold, silver and titanium) that are in contact with the GNDs. To obtain photoelectrical characteristics, we employed density functional theory to solve the non-equilibrium Green's function. Photo-responsivities and quantum efficiencies obtained for these nanostructures were far better than those for structures based on graphene nanoribbons. Among the proposed photodetectors, the best performance belonged to the bilayer structures illuminated by in-plane polarized incident light. The proposed photodetectors operate without a need for externally applied voltage and are suitable for parallel light propagation using directional couplers based on the evanescent field of incident light; hence, they have applications in optical integrated circuits. [ABSTRACT FROM AUTHOR]