Optical and Quantum Electronics最新文献

Herein, for the first time, we report the generation and direct dark-field imaging of photonic jets (PJs) of single dielectric microspheres illuminated by evanescent waves generated using narrow and broadband radiation from a supercontinuum source. The evanescent waves are generated on the surface of a prism by creating the total internal reflection of light within it. The images are recorded by varying the radius of the microspheres, ranging from 10 to 18 μm. The experimental images obtained with supercontinuum, blue, green, and red light are compared. The length and width of the PJs are found in the order of micrometers due to the large size of the microspheres. The proposed technique is simple and efficient in visualizing PJs, allowing for the simultaneous estimation of their length and width. It can also allow us to visualize the photonic nanojets, which have dimensions in the order of nanometers, usually generated from single tiny dielectric microspheres under evanescent illumination. For comparison, the theoretical simulations are performed on the PJs generated from single dielectric microspheres under non-evanescent (direct) illumination. Finally, the possible applications of the PJs generated by evanescent waves in different microscopy systems are reported here.

This study provides a detailed investigation into the structural, electronic, optical, and photovoltaic properties of the lead-free double perovskite Cs₂NaBiI₆ by integrating DFT, multi-platform device simulations (SCAPS-1D, wxAMPS, and COMSOL), and data-driven machine learning modeling. DFT calculations confirm a stable cubic Fm̅₃m phase with a lattice constant of 12.586 Å, and energy bandgap of 2.20 eV, indicating strong optical absorption in the visible region. The electronic band analysis reveals a lighter electron effective mass (mₑ = 0.617 m₀) and higher mobility (u_n = 28.5 cm²/V·s) compared with that of holes (mₕ = 1.26 m_o, u_h = 14.0 cm²/V·s), confirming electron-dominated transport. The effective density of states at 300 K was found to be Nc = 1.21 × 10¹⁹ cm⁻³ and Nv = 3.54 × 10¹⁹ cm⁻³. SCAPS-1D device simulation of the optimized AZO/Cs₂NaBiI₆/CuI configuration achieved a power conversion efficiency (PCE) of 23.31% with Voc = 1.23 V, Jsc = 21.80 mA/cm², and fill factor (FF) = 86.63%. Further optimization of the absorber thickness (800 nm), defect density (10¹⁵ cm⁻³), and interface parameters resulted in an efficiency enhancement of 25.22%. Cross-validation with wxAMPS and COMSOL showed excellent agreement, confirming the model’s robustness. Machine learning-based regression models (Linear, SVM, Random Forest, and XGBoost) were trained on simulation datasets; XGBoost achieved superior accuracy (R² ≈0.9993, MSE = 0.010) for PCE prediction. Feature-importance analysis identified defect density, doping concentration, and active layer thickness as the most critical determinants of PV performance. These combined theoretical, simulation, and machine learning findings establish Cs₂NaBiI₆ as a high-potential, and environmentally benign material for next-generation PSCs.

This paper proposes a graphene-based absorbing metasurface operating in the terahertz (THz) range, featuring switchable and tunable frequency bands. By applying a bias voltage to adjust the Fermi level of graphene, two distinct operating states can be achieved. When E_f = 1.1 eV, the absorption exceeds 90% within 2.8–8.7 THz; when E_f = 0.08 eV, strong absorption persists across 0.1–4.1 THz. In both frequency bands, the metasurface exhibits good impedance matching with free space. Furthermore, analysis using the phase cancellation metric confirms that the asymmetric configuration of the dielectric substrate is a key factor for broadband impedance matching. Based on the Drude model of graphene and the dispersion relation of surface waves, the observed blue shift in absorption with varying Fermi levels is explained.The metasurface maintains high absorption for both TE and TM waves under wide incident angles at E_f = 1.1 eV and E_f = 0.08 eV, achieving efficient absorption even at an incident angle of 60°. It also shows polarization insensitivity. The absorption mechanisms under the two operating states are analyzed using the equivalent circuit model and multiple interference theory, respectively, and the results are consistent with the simulations.The electric and magnetic field distributions further clarify the mechanism behind the efficient broadband absorption. In terms of fabrication and experimental design, reasonable improvements have been made based on existing strategies. Finally, a comparison with previous works demonstrates that the proposed metasurface achieves an integrated capability of dual-band switchability, tunability, and ultra-broadband absorption, showing great potential for applications in THz electromagnetic shielding, communication, and related fields.

Thanks to nonlinear effects, focusing, filtering, waveguide coupling, field enhancement, and other high degrees of optical tunability, resonant waveguide grating (RWG) has a broad scope of applications in science and industry, such as in solar cells, photodetectors, polarizers, spectrometers, filters, and biosensors. For field enhancement ability on the surface of RWGs for bioimaging and biosensing applications, a diverse range of parameters affect the electronic field distribution on the surface of RWGs, such as depth and period of grating, materials used to fabricate the grating, thickness, and refractive index of the layers around the grating. This research focuses on investigating the refractive index dependence of the resonance angle and the average value of the magnitude square of the electric field on the surface of the grating based on a simulation method. After optimizing the refractive index, an experiment was conducted to synthesize RWG and the real system, utilizing a grating to measure transmission and achieve good transmittance results.

Quantum Key Distribution (QKD) uses the principles of quantum mechanics to establish secure cryptographic keys among two or more parties. It includes encoding of the quantum state with the help of a quantum detector and quantum operations. Many QKD protocols have been developed to allow safe key establishment between two parties BB84, E91, etc. However, multiparty QKD is still remains a challenge due to the inherent principle of quantum mechanics like entanglement and observation. This paper puts a step ahead to establish a three-party QKD protocol that allows secure key establishment within a network. The proposed model is a closed three-party network architecture that uses the theory of bilocality. The model comprises three independent sources that share entangled particles with adjacent neighbors. The proposed QKD protocol provides a secret key distribution when measured with suitable observables and has potential applications like military operations that involve secure communication. The quantum bit error rate (QBER) and key generation rate guarantee efficient key establishment and security against eavesdropping in the network.

Optical intelligent reflecting surfaces (IRS) represent a breakthrough technology for enhancing free-space optical (FSO) communication flexibility and coverage. However, inherent optical signal characteristics render these systems critically vulnerable to malicious jamming, demanding robust resilience analysis. This work conducts a comprehensive jamming impact analysis under two practical scenarios: destination-directed and IRS-directed jamming. We develop novel channel models capturing the combined effects of path loss, atmospheric turbulence, pointing errors, and angle-of-arrival fluctuations. Closed-form expressions for the average bit error rate and outage probability are established for both intensity modulation/direct detection and heterodyne detection schemes. Asymptotic analyses reveal the diversity order and coding gain in high signal-to-noise ratio regimes. Monte Carlo validations demonstrate how jamming active probability, atmospheric conditions, and geometric alignment fundamentally govern system security. This study delivers essential design guidelines for optimizing IRS-assisted FSO systems against evolving jamming threats.

The source of terahertz (THz) radiation upon exposure of wide-bandgap semiconductors to femtosecond laser pulses in a magnetic field is photoexcited electrons. It is shown that a quantitative description of THz pulses generation can be achieved using confluent Heun functions. The electric field strength and total energy of THz pulse have been found for an arbitrary ratio of the size of photoexcited electron localization region to the characteristic wavelength of generated radiation. Numerical calculations of the field strength at the sample surface and the total energy have been performed for GaAs.

In this paper, we have demonstrated the generation of narrow spectral bandwidth pulse based on the chirped fiber Bragg grating (CFBG) and nonlinear polarization rotation (NPR) effects. Two CFBGs with different bandwidths are introduced into the laser system, respectively, to provide spectral filtering, which not only guarantee the output of the ultrafast solitons with narrow spectral bandwidth, but also allows the wavelength tunability. For the CFBG with 15 nm bandwidth, stable pulses with a pulse duration of around 10 ps and a narrow 3 dB spectral bandwidth of 0.4 ~ 0.6 nm are generated. Moreover, the wavelength of the narrow bandwidth pulses can be tuned from 1548.20 nm to 1556.60 nm by adjusting the PC. For the CFBG with 5 nm bandwidth, the narrowest bandwidth of 0.29 nm is achieved. Our researches provide a simple setup and method to obtain wavelength-tunable narrow bandwidth pulse outputs, showing the potential to meet various requirements of ultrafast laser applications.

Silver-doped cadmium sulfide (CdS) thin films were synthesized using the laser-assisted chemical bath deposition (LACBD) technique with Ag concentrations ranging from 1 to 5%. The main goal was to investigate the impact of carefully controlled silver (Ag) insertion on the structural, optical, and electrical properties of cadmium sulfide (CdS) films for optoelectronic applications, especially UV–visible photodetection. These changes were confirmed by material characterization through several techniques, which revealed substantial variations in the morphology, composition, and electronic properties of the materials with increasing silver content. The optical band gap was adjusted from 2.87 to 2.34 eV, and electrical tests indicated improved photodetection performance. At a doping level of 3% Ag, the performance of the films was exceptional. Several excellent parameters were measured at this concentration, such as responsivity of 1085.3 A/W, sensitivity of 5363.4%, gain of 54.63, and detectivity of 1.18 × 10¹² Jones. However, higher doping levels caused the creation of defects, which led to the reduction of device efficiency. These results point to 3% Ag-doped CdS thin films as new materials for UV–visible Photodetector with high sensitivity, and they also indicate the success of LACBD in modulating the optoelectronic properties of the thin film.

In this paper, we performed a detailed investigation on the evolution of a Double-half inverse Gaussian Hollow beam (DHIGHB) propagating through a gradient-index medium (GIM). The closed analytical expression for the DHIGHB in GIM was elaborated based on the Huygens–Fresnel diffraction integral formula. Numerical simulations are carried out to show the effects of the structural parameters of the incident DHIGHB and the gradient index parameter on the output beam evolution. The results show that the output beam exhibits a periodic evolution during propagation, with the self-focusing period increasing as the initial structure parameters increase. It is demonstrated that the self-repetitive behavior of the propagated can be controlled in the intensity and phase distributions beam by adjusting the waist size of the initial DHIGHB and the GIM parameter. These findings may be beneficial for applications of dark hollow beams in atomic trapping and fiber-optic communications.