Optical and Quantum Electronics最新文献

The ever-growing demand for high-speed data has challenged the conventional wireless transmission systems. In this paper, we propose a single-channel high-speed bandwidth-efficient free space optics (FSO) transmission by incorporating hybrid Polarization Division Multiplexing (PDM)-Orbital Angular Momentum (OAM) Multiplexing-Orthogonal Frequency Division Multiplexing (OFDM) using 16-level Quadrature Amplitude Modulation (QAM) signals. 2-OAM beams ((:{LG}_{text{0,0}}) and (:{LG}_{text{0,15}}):)of 2-orthogonal polarized beams are used to carry 640 Gbps of data over a free space channel by incorporating in-phase-quadrature modulation. At the receiver terminal, signal processing is implemented to rectify the signal distortion due to the free space channel losses. We analyzed the proposed system performance for varying weather conditions using standard performance metrics including constellation, Error Vector Magnitude (EVM), and Bit Error Rate (BER) over an increasing transmission range. The obtained results demonstrate reliable 640 Gbps transmission using the proposed system with a range varying from 703 m to 7 km within forward error correction (FEC) limits of BER ≤ 3.8(:times:{10}^{-3}), EVM ≤ 17.5%, and clear constellation.

Since its artificial synthesis, the adaptability of graphitic carbon nitride (g-C₃N₄) in solar energy conversion and environmental remediation has made it a promising photocatalyst. However, its practical applications are hindered by intrinsic limitations such as low surface area, rapid electron-hole recombination, and limited quantum efficiency. Rare-earth elements provide a useful technique to improve light harvesting and charge transfer under low-energy stimulation because of their distinct 4f electronic structure and upconversion luminescence. In this work, we successfully synthesize Er₂O₃/g-C₃N₄ heterojunctions rich in oxygen vacancies using a simple hydrothermal process. The introduction of oxygen vacancies modulates the charge-transfer pathway, accelerates carrier mobility, and improves electron–hole separation, thereby boosting CH₄ generation rates by 50.21-fold and 74.89-fold compared to pristine Er₂O₃ and g-C₃N₄, respectively. The exceptional photocatalytic performance originates from three synergistic effects: Er³⁺induced upconversion luminescence converts low-energy near-infrared photons into visible emissions, enhancing solar light utilization; oxygen vacancies broaden light absorption and expedite carrier migration; and these vacancies act as active sites that facilitate CO₂ adsorption and activation. This study not only demonstrates a high-efficiency photocatalyst for solar-driven CO₂ reduction but also provides an innovative design paradigm for engineering g-C₃N₄-based heterostructures with optimized charge dynamics and light management.

We introduce a mesoscopic quantum well whose confinement and chirality emerge solely from the intrinsic twist of a finite helicoidal metric. This purely geometric construction requires no external gates or fields: the metric itself induces both a harmonic radial potential and a twist-driven Zeeman-like term that breaks the (m leftrightarrow -m) degeneracy. By imposing hard-wall boundary conditions at (z = pm L/2), we quantize the axial motion and obtain a genuinely zero-dimensional helicoidal quantum dot. An exact analytic solution reveals an energy spectrum with chiral splitting linear in both the twist rate (Omega ) and the axial quantum number (n_z). For realistic InAs nanoroll parameters ((L = 100) nm, (Omega = 5times 10^{6},mathrm {m^{-1}})), this geometric effect results in a measurable splitting of (2hbar omega simeq 1.040) meV. We propose three viable experimental platforms, ultracold atoms in optical traps, femtosecond-written photonic waveguides, and strain-engineered semiconductor nanorolls, where this twist-induced phenomenon should be accessible with current technology.

We theoretically investigate enhanced mid-infrared absorption in a one-dimensional zero-contrast grating structure incorporating a thermally tunable vanadium dioxide ((hbox {VO}_{2})) layer atop a metallic substrate. At lower temperatures, (hbox {VO}_{2}) remains in its insulating phase with low optical loss, enabling it to function as a low-loss cavity spacer that supports Fabry-Pérot resonances under transverse magnetic polarization. When combined with the guided mode resonance effects induced by the zero-contrast grating, strong optical field confinement occurs within the (hbox {VO}_{2}) layer, leading to pronounced absorption peaks at mid-infrared wavelengths (16–19 (mu )m). We employ rigorous coupled-wave analysis to systematically analyze the optical responses, revealing that proper tuning of the grating period (9–12 (mu )m), fill factor (0.2(-)0.8), and (hbox {VO}_{2}) thickness (3(-)3.5 (mu )m) results in narrowband absorptance exceeding 90% at resonance. The underlying molybdenum layer acts as a back reflector to suppress transmission, further enhancing light trapping. The absorption characteristics can be significantly modulated by the thermally induced phase transition of (hbox {VO}_{2}), offering dynamic control over resonant absorption. Additionally, the structure exhibits azimuthal angle-dependent behavior and supports enhanced absorption even under transverse electric polarization. The interplay between guided mode resonance and Fabry-Pérot cavity effects in the low-loss (hbox {VO}_{2}) phase offers a passive route to achieve spectrally selective and thermally switchable absorption. These findings have potential applications in tunable infrared sensors, thermal emitters, and actively controllable photonic devices.

The present study investigates how organic pigments adhere to the TiO₂ surface, which acts as a mesoporous film in dye-sensitized solar cells (DSSCs). The effect of this adhesion on the electronic band gap is of interest. In this regard, eight different density functionals were evaluated to identify the most appropriate computational method to accurately describe the electronic and optical properties of TiO₂ nanoparticles. The results obtained for the absorption maximum (λ_max) and band gap energy (E_g) were compared with valid experimental data and it was found that the LSDA functional provides results closely matching benchmark values. Then, geometric optimization and time-dependent density functional theory (TD-DFT) calculations were performed on the adsorption of Naphthoquinone on TiO₂. These calculations identified two stable structures with interaction energies of − 0.49 and − 0.21 eV (TN1 and TN2, respectively), in the gas phase. The study of the absorption of natural dyes Acacetin and Juglone on these surfaces also showed that Juglone acted as a stronger chemisorption agent, with its interaction energy (E_int) being as low as − 0.27 eV and − 0.19 eV a significant charge transfer (~ 291, and 267 |me|) occurred, resulting in a significant reduction of the band gap by 23.29% and 44.57% in the TN1J1 and TN2J1 complexes, respectively. Density of states analysis confirmed the presence of new frontier orbitals, contributing to the improved of electronic conductivity. The optical absorption spectra also showed a shift towards longer wavelengths and an increase in absorption intensity for the dye-TiO₂ complexes, especially the Juglone-containing structures (TN2J1) with an absorption intensity of 0.1023, which improved the visible light harvesting ability. Overall, the results demonstrate the remarkable effect of functionalizing TiO₂ with Naphthoquinone-based natural dyes and introduce Juglone as a promising sensitizer. It improves efficiency and stability of dye-sensitized solar cells by enhancing the photophysical and electronic mechanisms.

This work presents an analytical model to optimize the efficiency of a mechanically stacked four-terminal (4-T) tandem solar cell composed of a (FAPbI₃)_1−x(MAPbBr₃)_x perovskite top cell and a Graphene/GaAs bottom cell. The perovskite absorber’s tunable bandgap, ranging from 1.52 to 2.31 eV, enables effective spectral matching with the fixed 1.42 eV bandgap of the GaAs subcell. The model incorporates experimentally validated optical and electrical parameters for subcells under AM1.5G illumination, allowing accurate modeling of the tandem device’s J–V characteristics. By systematically optimizing the absorber thickness and bandgap composition, the study demonstrates that a planar tandem configuration with top and bottom absorber thicknesses of 1 μm and 2 μm respectively can achieve a power conversion efficiency (PCE) of 28.3%. Implementing a textured surface on the top cell significantly enhances light trapping and reduces reflection losses, further increasing the PCE to 31.9%. This surface texturing improves photon absorption in the perovskite layer while maintaining sufficient light transmission to the bottom cell. The results identify an optimal top-cell bandgap of approximately 2.31 eV, balancing photon harvesting and transmission for maximal tandem efficiency. This work uniquely combines bandgap tuning, thickness optimization, and surface texturing in a 4-T perovskite/Graphene/GaAs tandem structure, offering practical insights for next-generation solar cell design.

While highly efficient solar cells use halide perovskites containing Pb, the unstable nature of the methylammonium (MA) cation at high temperatures interacting with lead iodide (PbI₂) lattice is challenging and may hinder the commercialization of these devices. Here, a method is proposed to completely prevent the organic cation rotation in MAPbI₃ perovskite by the substitution of CH₃COHNH₂⁺ (Ac) cation in the resonance form based on the calculations on structural, electronic and optical properties using Wien2k code with the FP-LAPW method. To observe the effect of Ac cation on power conversion efficiency (PCE), the structures of AcPbI₃ and MAPbI₃ perovskite solar cells (PSCs) with thin thicknesses (100–300 nm) are investigated using a solar cell capacitance simulator, numerically reproducing photocurrent–voltage characteristics and exciton generation rates of the perovskite structures. The electronic bandgap, optical conductivity, open-circuit voltage, photocurrent, fill factor, and PCE of AcPbI₃ PSC are found to be about 1.63 eV, 1340 Ω⁻¹ cm⁻¹ (in the visible region), 1.062 V, 24.90 mA cm⁻², 0.88, and 23.16%, respectively. Based on the electrical simulation results and a comparison of the proposed cation with the MA cation, a 29.74% efficiency improvement is achieved. Accordingly, the results envision a new path for the commercialization of PSCs with high efficiency and stability.

In this experimental work, Zn thin films were oxidized via annealing to produce transparent ZnO nanostructured films. The initial Zn thin films were deposited by DC magnetron sputtering and the annealing process was done at a temperature of 700 °C for different time intervals, i.e., 1, 2, 3, 4, and 5 h. Afterward, the effect of annealing time on structural, morphological, optical, and electrical properties was precisely investigated. X-ray diffraction studies verify a hexagonal wurtzite crystal structure for all ZnO thin films. The average crystal size of spherical ZnO nanoparticles which is obtained using Scherrer and Williamson-Hall methods is in good agreement with SEM images. Annealing for different time intervals influences surface roughness and average grain size of deposited films, which have been observed through AFM images. Optical characteristics of samples are obtained via absorption and transmission of UV spectra besides photoluminescence spectrum, confirming that direct optical energy bandgap -ranging from 3.19 to 3.26 eV for the samples- is directly influenced by annealing time. Thereafter, other optical parameters such as penetration depth, extinction coefficient, refractive index, dielectric constant, and optical conductivity have been calculated and discussed. Furthermore, a four-needle probe is adopted to measure ZnO thin films’ electrical resistance, which results in the calculation of resistivity and electrical conductivity. All results were well confirmed and validated by XPS testing. Hopefully, these results will facilitate the progress of high-efficiency optoelectrical devices produced by pure ZnO thin films.

Graphical abstract

In this study, the transmission of Super-Gaussian optical pulses through a one-dimensional photonic crystal containing two defect layers based on Weyl semimetal was investigated using the transfer matrix method and Fourier transform analysis. By leveraging the non-reciprocal enhancement provided by the Weyl semimetal and considering the spectral broadening of Super-Gaussian pulses compared to Gaussian pulses, transmitted energy, average pulse duration, and time delay were examined as key metrics for pulse transmission. The results demonstrate a significant dependence of these metrics on the pulse type and the direction of propagation incident on the structure. A comparative analysis with the transmission of Gaussian pulses highlights notable differences in the non-reciprocal behavior and transmission efficiency of Super-Gaussian pulses in the presence of topological defects, underscoring the crucial role of pulse shape in regulating direction-dependent light transmission in photonic architectures.

In this work, a fundamental single-band graphene-based biosensor structure is proposed, where the patterned graphene layer is designed in an octagonal geometry. Based on this configuration, dual-band absorbers are developed by integrating additional ring and plus-shaped resonators. All the proposed sensors share a simple three-layer configuration consisting of a metallic ground plane, a SiO₂ dielectric spacer, and a patterned graphene sheet functionalized by the target analyte. By optimizing the geometrical parameters and tuning the chemical potential and relaxation time of graphene, both the resonance frequencies and absorption intensity can be effectively controlled. The designed structures exhibit near-perfect absorption at their resonance bands and provide a compact and efficient platform for terahertz biosensing applications. The first proposed sensor shows a single absorption peak with 99.88% absorption and demonstrates promising results in detecting breast, cervical, and PC12 cancer cells, with the highest sensitivity of 2.14 THz/RIU observed for PC12 cancer cells. The second proposed sensor has two resonance bands, each exhibiting over 97.5% absorption, and shows notable sensitivity for detecting breast, Jurkat, and PC12 cancer cells, with the highest sensitivity of 4.21 THz/RIU observed for breast cancer at the second band. The third proposed sensor also has two resonance bands with over 98.5% absorption for each band and provides suitable sensitivity for detecting basal, cervical, and MCF-7 cancer cells, with the highest sensitivity of 1.66 THz/RIU observed for cervical cancer at the second band. The proposed technology offers a rapid and economical approach for oncological detection, enabling real-time tracking and tailored therapeutic strategies. All computational analyses were conducted using CST software.