Optical and Quantum Electronics最新文献

Vanadium dioxide (VO₂) is a remarkable phase-change material whose temperature-driven insulator-to-metal transition unlocks powerful tunability in the THz regime. Here, we present a VO₂-based metasurface that not only achieves over 90% absorption efficiency across a broad 1.27–2.64 THz range when in its metallic phase, but also transitions into a nearly perfect reflector (0.1–4 THz) in its dielectric phase. This striking dual functionality leverages the unique conductivity variation of VO₂ with temperature and is realized through a metasurface on a thin SiO₂ spacer backed by a gold layer. Notably, our design maintains insensitivity to both polarizations and incidence angle—crucial characteristics for practical THz applications—while offering a robust, wideband response. Through systematic analysis, we elucidate the physical mechanisms governing the high absorption and reflection, and demonstrate how key geometric parameters influence the device performance. By combining wideband tunability, angular and polarization invariance, and design simplicity, this metasurface holds substantial promise as a versatile component for next-generation THz technologies.

This study examines the propagation characteristics of an elegant Hermite Higher-order cosh-Gaussian beam (EHHOChGB) in atmospheric turbulence. Using the extended Huygens–Fresnel diffraction integral and Rytov method, a detailed analytical formulation for the average intensity of the EHHOChGB propagation in a turbulent is developed. Numerical illustrations and a discussion of the impact of turbulence strength on the intensity distribution under varying initial beam parameters conditions are presented. The obtained results show that the profile of the initial EHHOChGB remains essentially unchanged over short propagation distances. As the beam propagates further, a central peak in intensity gradually emerges at a specific propagation distance ultimately leading to a Gaussian-like profile in the far field. The speed of increase in the central peak intensity is observed to accelerate with higher turbulence strength or when beam parameters such as the beam order m and Gaussian waist width ω₀ are reduced. Furthermore, for small values of the decentered parameter b, the intensity of the central peak exhibits two distinct behaviors based on the parity of m. In contrast, the cosh power parameter N makes the beam more resistant to turbulence as it increases. The results could be valuable for practical applications of EHHOChGB in free-space optical communications and remote sensing.

The cumulative demand for high-speed and proficient data communication systems poses substantial challenges, including dispersion, inter-symbol interference (ISI), and fading effects in fiber-free-space optics (FSO) convergent networks. To address these issues, we propose and analyze, for the first time, a 100 Gbps probabilistic shaping (PS)-orthogonal frequency division multiplexing (OFDM)-based fiber-FSO convergent transmission system for near-generation smart communication applications. The proposed system enables the successful transmission of 100 Gbps data ([10 Gbps/wavelength × 5 wavelengths = 50 Gbps] × 2 states of polarization) over an 80-km single-mode fiber (SMF) link and a 600-m FSO link. The integration of PS and OFDM scheme enhances spectral efficiency within limited system bandwidth and extends transmission distance by mitigating the impacts of dispersion, ISI, and fading. Experimental results demonstrate the effectiveness of the proposed architecture, achieving a forward error correction code rate of 9/10 and a normalized generalized mutual information threshold of ~ 0.92. These results confirm the capability of the system to support flexible data rates and long-distance transmissions while ensuring reliability and efficiency. This work contributes to advancing fiber-FSO convergent systems, with potential future applications in scalable and adaptive communication networks.

This study investigates the effect of Ga, In, and (Ga, In) doping at 6.125% concentration on the structural, electronic, carrier lifetime, and optical properties of ZnO using density functional theory (DFT). The GGA + U (Generalized Gradient Approximation with On-Site Coulomb Interaction U) approach was employed to correct band gap underestimation, revealing a decrease in band gap from 3.38 eV (pure ZnO) to 3.24 eV (Zn₁₄Ga₂O₁₆), 2.93 eV (Zn₁₄In₂O₁₆), and 3.07 eV (Zn₁₄GaInO₁₆). Formation energy analysis confirmed the thermodynamic stability of the doped structures, while the Fermi level shift into the conduction band indicated n-type behavior. Partial density of states (PDOS) analysis showed significant contributions from Ga-s, In-s, Zn- (p, s), and O-s orbitals, modifying the electronic structure. Effective mass calculations revealed a reduced ({m}_{e}^{*}/{m}_{h}^{*}) ratio, enhancing carrier lifetime by minimizing recombination. Optical studies demonstrated an increased probability of electron transitions at lower energies and improved visible-light absorption, particularly after (Ga, In) co-doping. These results suggest Zn₁₄GaInO₁₆ as a promising candidate for use in solar cell and optoelectronic devices.

This study explores the optical and plasmonic properties of the gold/rubidium nanocomposite, wherein gold nanoparticles (AuNPs) are uniformly embedded into a coherently prepared rubidium (Rb) atomic media. This study takes into account the effects of the size, shape and volume fraction of AuNPs, and control field frequencies using localized surface plasmon resonance and atomic transitions in rubidium. Using a four-level atomic cascade configuration, this Au/Rb nanocomposite can be modeled to accurately manipulate its nonlinear optical response. The effective dielectric function of this nanocomposite is modeled to show significant tunability in the real and imaginary components through external control fields. In this study, we found that plasmonic response induced by the AuNps could give rise to the enhancement of the Au/Rb optical properties by having a very significant scope for applications in quantum photonics, plasmonic sensing, and tunable nanophotonic devices. This work highlights the powerful integration of plasmonic nanostructures with atomic systems, presenting innovative opportunities for advanced photonic technologies.

Ternary polypropylene/polyamide6/organoclay composites were successfully synthesized through a melt-mixing process, with and without a compatibilizer. The chemical-bond, structural, and morphological characteristics of composites were thoroughly investigated utilizing Fourier-transform infrared spectroscopy, wide-angle X-ray diffraction, and scanning electron microscopy analyses. The morphological investigations showed that the addition of a compatibilizer to the composite leads to a reduction in the size of the dispersed PA6/clay domains and a decrease in the distance between them due to the formation of a PP-g-PA copolymer at the interface, which improves compatibility between the PP and PA6 phases. Furthermore, the differential scanning calorimetry technique was employed to assess the crystallization and thermal action of the composites. The results revealed that the addition of a compatibilizer resulted in a slight increase in the crystallization temperature of PP and a reduction in the overall crystallinity of the composite, attributed to the compatibilizer’s interaction with both the clay and PA6/clay islands, limiting PP chain mobility and hindering crystallization. The band gap energies were determined in a range of 4.17–4.34 eV by diffuse reflectance spectroscopy and utilizing the Tauc method. Notably, this study marks the first instance of exploring the nonlinear optical properties of these composites. This was achieved by employing Z-scan technique by subjecting the samples to a continuous-wave Nd:YAG laser functioning at a wavelength of 532 nm. A positive nonlinearity of the order of 10^–8 cm²W⁻¹ was observed across all samples studied. Particularly noteworthy was the significant enhancement in nonlinear refractive index and absorption coefficients for polypropylene/polyamide6/organoclay ternary composites upon the addition of the compatibilizer. These findings strongly indicate the potential of these composites for applications in nonlinear optical devices and technologies.

The acoustic characteristics of one-dimensional generalized Thue-Morse quasi-periodic structures using serial closed resonators with varying cross-section areas are examined in this work. The localization and the acoustic band gap features are analysed by systematically altering the complexity of the generalized Thue-Morse sequences. The findings show that higher-order generalized Thue-Morse sequences introduce stronger localized modes and wider acoustic band gaps, which allow for control over wave propagation. We demonstrated the role of using resonators with different cross-section areas to enhance wave confinement and band gap tunability. Results show the potential use of the proposed generalized Thue-Morse structures in high-sensitivity sensors, multi-frequency resonators, and tunable filters, among other advanced acoustic applications.

In photovoltaic (PV) systems, maximum power point tracking (MPPT) technologies are used to constantly maximize PV output power, which is primarily governed by solar radiation and cell temperature. However, the typical MPPT approach wastes a significant amount of energy, and the efficiency is cumbersome and unstable. To solve these limitations, the Jordan neural network (JNN) MPPT with FOPID-SEPIC converter is employed in this research. As a result, the PV and non-linear load were constructed, and three scenarios were tested to validate the proposed PV design: normal, static, and dynamic. At first, the PV model with a non-linear load was designed for a certain range. This specially designed model is used to collect voltage, temperature, power, current, and irradiance under a variety of situations. The acquired parameters were given to JNN MPPT, which was specifically designed for maximum PV power tracking. The FOPID obtained the error value for JNN output and PV generator power. The FOPID consists of five parameters that are optimally chosen using brown bear optimization to produce a better process. FOPID generates a pulse signal to the SEPIC convertor, which powers the non-linear load after figuring out the optimal value. Consequently, the observed error of the JNN is 0.0033%, the accuracy rate is 0.99%, and the false positive rate (FPR) is 0.04%. The suggested JNN MPPT model functioned well in comparison to alternative strategies, resulting in appropriate implementation in actual tracking ways.

In this article, a κ-Ga₂O₃ cap layer is introduced as gate dielectric to achieve E-mode GaN p-channel heterostructure FETs (p-HFETs). Due to the high spontaneous polarization of κ-Ga₂O₃, 2DEG that up to 1.51 × 10¹⁴ cm^− 2 are induced at the κ-Ga₂O₃/GaN interface. Based on device simulations, the threshold voltage (V_TH) can reach a high value of -2.42 V and maintain negative even when the thickness of the GaN channel (t_ch) is increased to 50 nm. By interconnecting base and gate to form a double-gate (DG) structure, the control of 2DEG and 2DHG can be realized. The results show that p-HFETs with DG structure not only exhibit a threefold increase in the on-current (I_ON) while maintaining the E-mode operation, reaching 24.87 mA/mm with V_TH of -1.25 V, but also reduce the gate leakage current at forward bias. Furthermore, the utilization of κ-Ga₂O₃ as the gate dielectric results in an enhancement of the gate breakdown voltage to -35.8 V. The proposed DG p-HFETs represent a promising approach to achieving high-performance enhancement mode p-channel GaN devices.

The paper presents the analysis and discussions on a Surface Plasmon resonance (SPR) based Photonic Crystal Fiber (PCF) Refractive index (RI) Biosensor, designed specifically to detect two of the most widespread diseases—HIV-caused AIDS and Sickle cell anaemia. The detection is purely dependent on the RI of the affected cells (1.42 for HIV and 1.38 for Sickle cell anaemia), compared to 1.35 for normal cells. The proposed RI biosensor has concave-shaped microchannels on either side of the PCF acting as a channel, where the plasmonic material interacts with the bio-analytes of HIV-infected and sickle cells. Additionally, a layer of MXene, an emerging 2D plasmonic enhancer is coated on the microchannels, to enhance the sensor performance in terms of sensitivity and confinement loss. Moreover, the optimized structure achieved wavelength sensitivities of 10,571.43 nm/RIU and 3500 nm/RIU for the Gold PCF sensor, and 14,142.86 nm/RIU and 4000 nm/RIU for MXene-Gold PCF sensor for HIV-infected cell and Sickle cell anaemia, respectively. Hence, the proposed SPR biosensor using MXene has the potential for the early detection of HIV and Sickle cell anaemia.