We studied the pressure-dependent structural, electronic, elastic and optical characteristics of cubic LiCaBr₃ by first-principles DFT calculations. Our findings reveal that the lattice parameter gradually decreases from 0 to 60 GPa. The increase in interatomic interactions under pressure results in changes in the electronic band structure and shifts in the density of states around the Fermi level. Moreover, the pseudogap shift to the left of the Fermi level with increasing pressure, implying an electronic structure change. The energy peaks in the valence band shift to lower energy levels, and covalency increases with pressure. The mechanical properties indicate that LiCaBr₃ remains ductile throughout the investigated pressure range, although its ductility gradually decreases with increasing pressure. The Pugh ratio (B/G) decreases from 2.43 at 0 GPa to 1.82 at 60 GPa, remaining above the critical value of 1.75. This pressure-induced stiffening, reflected by the substantial increase in the elastic moduli, is accompanied by a gradual decrease in the Pugh ratio from 2.43 to 1.82, while remaining above the ductile-to-brittle threshold of 1.75. Moreover, the Cauchy pressure becomes increasingly negative at higher pressures, reaching −36.06 GPa at 60 GPa, indicating an enhanced directional/covalent character of bonding under compression. Our findings may provide useful theoretical guidance for future experimental studies toward the development of electronic devices based on the compounds studied for photovoltaic and optoelectronic applications.
Passively Q-switched lasers have become essential sources of short optical pulses due to their simplicity, compactness, and high peak power. In parallel with the growing demand for spectrally versatile laser sources, multi-wavelength Q-switched operation has attracted increasing interest in both fiber and solid-state laser platforms. In contrast to conventional single-wavelength Q-switched lasers, multi-wavelength systems exhibit richer spectral and temporal dynamics resulting from gain competition, wavelength-dependent saturable absorption, and intracavity filtering effects. This review provides an in-depth discussion of the physical mechanisms, gain media, saturable absorbers (SAs), and cavity architectures that enable passively Q-switched multi-wavelength laser operation. Recent experimental progress in fiber and solid-state lasers is critically examined, with particular emphasis on pulse characteristics, wavelength stability, and energy distribution among lasing lines. Finally, the challenges limiting practical implementation and the prospects for tunable, power-scalable, and mid-infrared multi-wavelength Q-switched laser sources are discussed.
Blue laser-driven white light sources have attracted considerable attention for high-power lighting because of their high luminance and excellent directionality. However, thermal degradation and color instability during continuous operation remain major challenges. In this study, the optical properties of a commercial Ce³⁺-activated YAG yellow phosphor (NYAG, Intematix, USA), commercial GAL aluminate phosphors (GAL545 and GAL555, Intematix, USA), and phosphor-in-glass (PIG) structures were systematically investigated under blue laser excitation by considering phosphor concentration, continuous operation, red phosphor incorporation, and structural parameters. NYAG exhibited high luminous flux but significant thermal-induced color instability during prolonged excitation, whereas GAL545 demonstrated superior thermal stability while maintaining high luminous performance. Red phosphor incorporation effectively improved color rendering and reduced correlated color temperature, although excessive addition decreased luminous efficiency. In PIG structures, phosphor thickness and emission area significantly affected the balance between luminous efficacy and color quality. These results provide practical design guidelines for developing thermally stable and color-tunable laser-driven white light sources for high-power lighting applications.
This study examines the impact of the orbital angular momentum (OAM) of two vortex coupling fields on the Hartman effect in a one-dimensional photonic crystal. The defect layer doped by vee-ladder type four-level atoms containing a Rydberg state. By adjusting the Rydberg atoms along with the vortex coupling fields, the Hartman effect can effectively be controlled solely by the OAM. In addition, we found that the probe field transmission is also increased with proper choice of OAM of the vortex coupling beams.
Defect-assisted recombination, unfavorable interfacial band alignment, and transport losses remain major barriers to realizing the theoretical efficiency potential of lead-free Sn-based perovskite solar cells. To systematically investigate these limitations, planar (FA)0.5(MA)0.5SnI3 devices were numerically analyzed using the SCAPS-1D drift–diffusion framework, with the objective of identifying optoelectronic performance trends, dominant loss mechanisms, and theoretical operating limits rather than predicting directly realizable experimental efficiencies. A range of commonly reported electron transport layers (CdS, PC61BM, SnS2, and WS2) and hole transport layers (CdTe, CuI, MoO3, MoS2, NiO, and PTAA) were systematically screened to evaluate the influence of energy-band alignment and carrier selectivity on device behavior. Parametric analyses of absorber thickness, bulk defect density, defect energy position, carrier-capture cross-section, background doping, and parasitic series and shunt resistances were performed to elucidate the dominant loss mechanisms governing short-circuit current density, open-circuit voltage, fill factor, and power conversion efficiency. Among the investigated configurations, the optimized FTO/WS2/(FA)0.5(MA)0.5SnI3/CuI/Au device architecture exhibited favorable optoelectronic characteristics, yielding a simulated PCE of 27.92
This simulation-based study uses SCAPS-1D to design and optimize silver sulfide (Ag₂S) solar cells in both bulk and quantum dot (QD) absorber configurations. Ag₂S, a low-cost and environmentally benign material, was investigated with absorber sizes ranging from bulk to 10 nm, 5 nm, 3 nm, and 2 nm QDs. Parameters for QDs smaller than 10 nm are extrapolated using quantum confinement theory and have not been experimentally confirmed; these simulations represent a theoretical exploration of extreme quantum confinement. This simulation-based study uses SCAPS-1D to design and optimize silver sulfide (Ag₂S) solar cells in both bulk and quantum dot (QD) absorber configurations. For QDs smaller than 10 nm, SCAPS-1D treats the absorber as a homogeneous effective medium and cannot explicitly model ligand chemistry, interdot tunneling, or energetic disorder. Therefore, results for 5 nm, 3 nm, and 2 nm QDs should be interpreted as hypothetical sensitivity analyses exploring quantum confinement trends, not as quantitative predictions for real devices. Within this framework, bulk Ag₂S and 10 nm QDs achieved the highest simulated efficiencies (16.60
Two-dimensional Ruddlesden-Popper (2DRP) halide perovskites have emerged as promising absorber materials for perovskite solar cells (PSCs) due to their conveniently modified optoelectronic properties, high power conversion efficiency (PCE), and enhanced durability against environmental influences. In this work, a detailed SCAPS-1D simulation study to optimization of a lead-free, all inorganic 2DRP PSC with Cs2SnI2Br2 as the active photoabsorber layer. The absorber exhibits an optimal bandgap of 1.4 eV, superior electrical conductivity, and thermal stability, thus being making an effective alternative to toxic Pb-based perovskites. A detailed interfacial band alignment analysis highlight that out of four hole transport layers (Cu2O, CuSCN, CuI, and Spiro-OMeTAD), Cu2O offers the most favorable valence band offset (-0.26 eV) with Cs2SnI2Br2 that supports effective hole collection and minimize recombination at the interfaces. Additional optimization of device structure FTO/SnO2/Cs2SnI2Br2/Cu2O/Ni, confirmed better carrier transport and well matched energy-level, with optimum parameters of absorber thickness (500 nm), acceptor dopant concentration (1 × 1017cm− 3), and trap density (1 × 1014 cm− 3). The analysis further showed that low series resistance coupled with high shunt resistance enhance charge extraction, while Ni with a work function of 5.5 eV forms a good ohmic contact with Cu2O, reducing back contact losses. Temperature-dependent analysis gives an activation energy of Ea = 1.49 eV, while C-V/Mott-Schottky analysis confirmed a built-in potential of Vbi =1.2 V for the optimized device. The optimized device reached a PCE of 28.81
In this research work, a highly sensitive Surface Plasmon Resonance (SPR) based D-shaped Photonic Crystal Fiber (PCF) refractive index (RI) sensor is proposed. The analysis and simulation is done using COMSOL Multiphysics, a Finite Element Method solver. A gold (Au) layer is deposited on a flat surface of a D-shaped PCF, followed by an MXene layer, which boosts the interaction of surface plasmons with biomaterials. The sensor design exhibits a novel Au/MXene hybrid plasmonic structure to further enhance the interaction and advance the performance. The simulation results for the proposed sensor design are evaluated for biologically viable refractive indices varying from 1.31 to 1.36. The parametric analysis is conducted by varying critical structural parameters to ensure optimal biosensor performance is achieved, thereby maximizing sensitivity. Simulation outcomes indicate that the proposed sensor is capable of reaching a maximum wavelength sensitivity of 8000 nm/RIU, thereby establishing its capability to measure minute refractive index changes with high precision. This enhanced sensitivity parameter, in combination with improved amplitude characteristics, makes the proposed sensor a viable alternative for the domains like biomedicine, chemical measurements, and environmental monitoring, where traditional biosensing methods are prone to low refractive sensitivity limits.
Tungsten trioxide (WO3) is a widely used semiconductor photocatalyst for environmental photocatalytic remediation, but its practical application is severely limited by inherent drawbacks: wide band gap, poor visible light response, and rapid recombination of photogenerated electron-hole pairs. In this study, a Bi2S3/Bi2MoO6/WO3 double type-II heterojunction heterojunction photocatalytic film was rationally fabricated through a sequential hydrothermal-solvothermal-in-situ growth strategy. Bi2S3 quantum dots were uniformly loaded on the Bi2MoO6/WO3 hierarchical structure, forming a ternary heterojunction with tight interfacial contact and efficient charge transfer channels. The photoelectrochemical and photocatalytic performance of the as-prepared material was optimized by tuning the in-situ growth time of Bi2S3. The optimal BS/BMO/WO3(1 h) sample has an extended light absorption range up to 700 nm, a high transient photocurrent density of 46 µA·cm− 2, and effectively improved separation and transport efficiency of photogenerated carriers. Under simulated sunlight irradiation at pH = 3, this sample achieved a 74.4
This work not only establishes Ag2S-based devices as promising lead-free alternatives but also offers a strategic framework for designing cost-effective, stable, and environmentally sustainable solar cells through rational material selection and structural optimization. This study provides an extensive numerical evaluation of Ag2S-based photovoltaic (PV) devices incorporating ZrS2 as a buffer layer and a range of hole transport layers (HTLs) such as V2O5, WS2, SnS, Cu2O, CsSnI3, GeSe, WSe2, and MoS2. The primary goal is to optimize the structural and electronic parameters to enhance overall solar cell performance. Systematic SCAPS-1D simulations were conducted to assess the influence of absorber layer thickness, doping concentration, and defect density on key photovoltaic characteristics, including power conversion efficiency (PCE), open-circuit voltage (VOC), short-circuit current density (JSC), and fill factor (FF). Among the studied HTLs, V2O5 exhibited superior electronic compatibility with the Ag2S absorber, achieving an impressive PCE of 32.44
In the present work samarium doped strontium lithium borosilicate glasses were prepared by using melt quenching technique incorporating different concentrations of samarium ions. The amorphous nature was confirmed by XRD technique. The FT-IR spectra indicates the presence of BO3 and BO4 units based on their stretching vibrations and the extra related bonding nature. The glass transition temperature (Tg) of as-prepared glass samples was determined using the Differential scanning calorimetry (DSC) data. From absorption spectra, the optical band gap and Urbach energy observed to decrease with increasing Sm3+ concentration, with nephelauxetic ratios hinting at mostly covalent Sm–O bonds. The optical features were analyzed using the band gap values derived from the Tauc plot. Judd–Ofelt (J–O) theory was applied to evaluate the phenomenological intensity parameters (Ω4 > Ω6 > Ω2) showing the highest value of Ω4 implying strong Sm–O bonding. The PL Spectra showing four emission bands corresponding to the transition 4G5/2→6H5/2, 6H7/2, 6H9/2, 6H11/2. Dexter theory and the Inokuti–Hirayama (I–H) model were employed to investigate the interactions involved in the non-radiative energy transfer process. The CIE coordinates (x, y) and CCT values were calculated from the PL emission data, and the results indicate that the glasses exhibit emission in the reddish–orange region. Temperature-dependent Photoluminescence (TDPL) also confirmed a progressive increase in structural rigidity of the glass network and chromatic stability under thermal stress up 175 °C. The Time Resolved Photoluminescence (TRPL) technique helps to find out the average lifetime (τavg) of the samples, which decreases significantly with the increase in concentration of Sm3+. Overall, the as-prepared glass samples are found to be reliable and suitable candidates for reddish-orange luminescent devices and as a potential red-emitting component in w-LEDs.
Directly modulated Vertical Cavity Surface Emitting Lasers (VCSELs) operating at 1550 nm are attractive optical sources due to their low power consumption, low threshold current, and ease of integration. However, their application in long haul optical communication systems is limited by their frequency chirp, which significantly enhances chromatic dispersion and hence induces signal degradations. This work investigates the use of Fiber Bragg Grating (FBG) based chirp compensation to improve the transmission characteristics of a 10 Gbps VCSEL link over 100 km of single mode fiber (SMF). Three transmission configurations were designed and analysed using OptiSystem, including a conventional Dispersion Compensating Fiber (DCF)-compensated link and two FBG-assisted architectures. The impact of VCSEL chirp on spectral broadening and transmission quality was evaluated through optical spectrum, eye-diagram, BER, Q-factor and received signal power analyses. An FBG was employed to compensate chirp-induced impairments and optimize signal propagation over the long haul fiber span. The results show that the conventional DCF-only configuration provides inadequate performance, whereas the inclusion of an FBG significantly enhances signal quality. The best performance was achieved when the FBG was positioned before the transmission fiber, yielding a Q-factor of approximately 9.39 and a BER in the order of 10⁻21 while reducing the required DCF length from 24 to 10 km. The proposed work demonstrates that the FBG-based chirp compensation is an effective technique for extending the transmission reach of the directly modulated 1550 nm VCSELs, making them promising solutions for future high-speed optical communication networks.
In this work, an asymmetric double quantum well (ADQW) structure is investigated to evaluate the feasibility of its unique operating principle, based on a precise design of the third energy level. Unlike many ultrafast photodetectors that rely on thermally-driven mechanisms−which are inherently sensitive to ambient temperature variations - the proposed ADQW demonstrates intrinsic thermal stability. Although the device exhibits pronounced temperature-dependent effects, the underlying mechanism remains robust and functional over a wide temperature range from 20 K to 293 K. The operation of the structure relies on purely quantum mechanical inter-sub-band transitions (ISBT) and a built-in self-induced electric field (SIEF) generated via doping modulation (DM), enabling a photovoltaic effect with an ultrafast response. Consequently, by overcoming the limitations of thermal instability, this nanoscale structure represents a highly adaptable and promising electro-optic component for effective integration with broader electronic and optoelectronic systems.
The efficiency of solar cells is primarily constrained by intrinsic factors even when optimal fabrication methods are adopted. Tandem solar cells have captivated the research community by providing higher efficiencies and utilizing sun spectrum effectively, owing to their unique structure. This work presents a numerical analysis of highly efficient all-perovskite tandem solar cells using lead-free CsBi3I10(band gap 1.75 eV) and low-lead mixed halides MAPbI1-x Clx (band gap 1.55 eV) and FAPbI3 (band gap 1.61 eV) perovskites via SCAPS-1D simulations. The performance of three tandem structures are evaluated: Structure 1 (STR1) with TiO2 (ETM)/CsBi3I10/Cu2O (HTM) as the Top-cell and TiO2 (ETM)/MAPbI1-x Clx /Cu2O (HTM) as Bottom-cell), Structure 2 (STR2) with ZnO (ETM)/CsBi3I10/CuSCN (HTM) as the top-cell and TiO2 (ETM)/MAPbI1-x Clx/CuSCN (HTM) as Bottom-cell and Structure 3 (STR3) with TiO2 (ETM)/CsBi3I10/Cu2O (HTM) as the Top-cell and TiO2(ETM)/FAPbI3/Cu2O (HTM) as bottom-cell. The key photovoltaic parameters including short-circuit current (Jsc), open-circuit voltage (Voc), power conversion efficiency (PCE) and fill factor (FF) were calculated for all device structures. In addition, the wavelength-dependant quantum efficiency was plotted, and a comprehensive analysis was performed to assess how variations in perovskite layer thickness, ETL/HTL acceptor and donor concentrations and perovskite layer defect density influence overall tandem cell performance. Optimization was carried out to enhance device efficiency. The simulation results show that STR1 and STR2 achieves PCE’s of 36.80
Image steganography, the art of concealing secret data within digital images, has become increasingly vital for secure communication. Traditional methods face limitations in data hiding capacity, statistical detectability, and robustness to transformations. Modern approaches, leveraging deep learning, particularly Generative Adversarial Networks (GANs), have shown promise in increasing embedding capacity and robustness. However, the imminent threat of quantum computing necessitates post-quantum cryptographic solutions. This paper introduces PQ-TransSteg, a novel quantum-resilient image steganographic framework that integrates asymmetry-aware compression, post-quantum cryptography, and TransformerGAN for adaptive, high-capacity embedding. Symmetry-based Graph Fourier Transformations (GFTs) reduce redundancy, maximizing embedding efficiency while preserving structural fidelity. The hybrid cryptographic layer, combining CRYSTALS-Kyber and AES, ensures confidentiality, integrity, and resistance to active MitM attacks. The TransformerGAN architecture, with multi-head self-attention, generates visually indistinguishable stego-images. Experimental results on DIV2K and COCO datasets demonstrate superior performance, achieving PSNR values up to 45.91 dB, SSIM to 0.989, and payload capacity up to 4.0 bpp, with near-random detection accuracy in contemporary steganalysis models.
The structural, magnetic, electronic, optical, thermoelectric, and thermodynamic properties of the Heusler compound TiFe2Sn were investigated using first-principles calculations based on density functional theory (DFT) within the full-potential linearized augmented plane wave (FP-LAPW) method. Structural optimization performed employing the generalized gradient approximation (GGA-PBE) confirms a stable cubic phase with a lattice constant of 6.0358 Å and negative formation energy, indicating thermodynamic stability. Electronic band structure calculations using the modified Becke-Johnson (Tb-mBJ) potential reveal an indirect band gap of 0.6 eV, consistent with the compound’s semiconducting nature. Optical analysis indicates strong absorption in the UV–visible range and a plasmonic-like response at higher energies, supporting potential applications in optoelectronic and plasmonic devices. Thermoelectric properties, evaluated using semi-classical Boltzmann transport theory under the Constant Relaxation Time Approximation (CRTA), yield a maximum theoretical figure of merit (ZT) of approximately 0.97 at 300 K. Because the lattice thermal conductivity was not calculated from first principles, this value should be interpreted as an ideal upper-limit estimate of the material’s thermoelectric performance. Moreover, thermodynamic parameters including heat capacity, thermal expansion, Debye temperature, entropy, and bulk modulus were analyzed using the quasi-harmonic Debye model. Overall, the present work provides a comprehensive understanding of the multifunctional properties of TiFe2Sn and suggests that it is a promising candidate for future thermoelectric and optoelectronic applications. However, further investigations are required to assess its practical device performance.
In this paper, A compact fiber-optic interferometric sensor for simultaneous refractive index (RI) and temperature sensing is proposed and numerically investigated. The sensor is based on a graded-index multimode fiber (GI-MMF) incorporating a conical cavity coated with a ZnO thin film. The sensing principle is based on the combined use of spectral shift and reflected intensity modulation, enabling effective discrimination between RI and temperature variations. Two sensor configurations, referred to as Sensor A and Sensor B, were comparatively analyzed. The proposed sensor architectures exhibited refractive index sensitivities reaching −11.21 nm/RIU and 47.2 nm/RIU for Sensors A and B, respectively, while the corresponding temperature sensitivities were 2.84 pm/°C and 6.4 pm/°C. The thermal cross-sensitivity affecting RI measurements was estimated to be 2.53 × 10⁻4 RIU/°C for Sensor A and 1.35 × 10⁻4 RIU/°C for Sensor B, indicating a superior thermal immunity of the latter configuration. The results reveal that RI variations are primarily encoded through spectral wavelength shifts, whereas temperature changes are predominantly reflected in signal amplitude modulation. This dual-parameter interrogation strategy significantly minimizes parameter crosstalk while enhancing measurement selectivity. Owing to its compact design, low thermal cross-sensitivity, and enhanced sensing performance, the proposed architecture represents a promising platform for multiparameter fiber-optic sensing in environmental, industrial, and biomedical applications.
Graphene-based electro-optic modulators have attracted considerable attention for next-generation photonic integrated circuits because of their high carrier mobility, electrically tunable optical properties, and compatibility with silicon photonics. In this work, a new suspended dual-layer graphene slot-waveguide electro-optic phase modulator operating at the 1550 nm telecommunication wavelength is proposed and numerically investigated. Unlike conventional single-layer graphene modulators, the proposed architecture employs two suspended graphene layers embedded within a nanoscale slot waveguide to strengthen light–matter interaction and improve phase-modulation efficiency. The device performance was systematically analyzed using Ansys Lumerical MODE Solutions by investigating the effects of slot width, etch width, silicon-arm dimensions, and graphene chemical potential on the effective refractive index, wavevector, propagation loss, and phase shift. The simulation results reveal that an optimized slot width of approximately 80 nm and an etch width between 100 and 200 nm provide the most favorable balance between optical confinement and modulation performance. The proposed structure exhibits quasi-linear variation in wavevector and very low propagation loss over the graphene chemical-potential range of 0.4-1.0 eV, making it highly suitable for phase modulation. The optimized device achieves a voltage–length product of approximately 0.09 V·cm, an insertion loss of only 0.48 dB, an estimated switching energy of 0.375 pJ/bit, and an intrinsic RC-limited bandwidth of 133 GHz. A comparison with recently reported graphene-based modulators demonstrates that the proposed design provides a suitable trade-off among modulation efficiency, device footprint, bandwidth, optical loss, and power consumption. These results indicate that the proposed suspended dual-layer graphene slot-waveguide architecture is a promising candidate for compact, low-loss, and high-speed electro-optic phase modulators for future silicon photonic integrated circuits.
This study presents a cost-effective dual channel humidity sensor. The sensor is fabricated using an innovative fiber-braiding technique. The sensor setup integrates three polymer optical fibers that braid together into a compact structure. Among the three fibers, one is the main input fiber and the other two are independent output fibers designated as Channel-1 and Channel-2. The sensor’s dual channel output configuration enables simultaneous, real-time monitoring of relative humidity with built-in cross-validation. The sensor response of one channel can be directly compared to the other channel under identical excitation and environmental conditions. Experimental evaluation demonstrates that the proposed sensor setup exhibits highly consistent performance across a relative humidity range of 30
