Search Results (1,853)

This study investigates the influence of vacancy engineering and nitrogen doping on the structural, electronic, and optical properties of T-graphene fragments (TFs) using density functional theory (DFT) and time-dependent DFT (TD-DFT). A central vacancy and five pyridinic nitrogen doping configurations are explored to modulate the optoelectronic behavior. All systems are thermodynamically stable, exhibiting tunable HOMO–LUMO gaps, orbital distributions, and charge transfer characteristics. Optical absorption spectra show redshifts and enhanced oscillator strengths in doped variants, notably v-NTF2 and v-NTF4. Nonlinear optical (NLO) analysis reveals significant enhancement in both static and frequency-dependent responses. v-NTF2 displays an exceptionally high first-order hyperpolarizability (⟨β⟩ = 1228.05 au), along with a strong electro-optic Pockels effect (β (−ω; ω, 0)) and second harmonic generation (β (−2ω; ω, ω)). Its third-order response, γ (−2ω; ω, ω, 0), also exceeds 1.2 × 10⁵ au under visible excitation. Conceptual DFT descriptors and energy decomposition analysis further supports the observed trends in reactivity, charge delocalization, and stability. These findings demonstrate that strategic nitrogen doping in vacancy-engineered TFs is a powerful route to tailor electronic excitation, optical absorption, and nonlinear susceptibility. The results offer valuable insight into the rational design of next-generation carbon-based materials for optoelectronic, photonic, and NLO device applications. Full article

Terahertz (THz) has attracted substantial attention owing to its unique advantages in high-speed communications. However, conventional THz waveguide systems are inherently constrained by high transmission losses, stringent fabrication precision requirements, and extreme sensitivity to structural defects. Topological edge states with topological protection have driven significant advancements in THz wave manipulation. Nevertheless, the width of the topological waveguide based on edge states remains restricted. In this work, we put forward a type of spin photonic crystal with three-layer heterostructures, where large-area topological waveguide states are demonstrated. The results show that these topological waveguide states are localized within the region of Dirac photonic crystals. They also display spin-momentum-locking characteristics and maintain strong robustness against defects and sharp bends. Furthermore, a THz beam splitter and a topological beam modulator are implemented. The designed heterostructures expand the applications of multi-functional topological devices and provide a prospective pathway for overcoming the waveguide bottleneck in THz applications. Full article

Highly integrable silicon carbide (SiC) has emerged as a promising platform for photonic integrated circuits (PICs), offering a comprehensive set of material and optical properties that are ideal for the integration of nonlinear devices and solid-state quantum defects. However, despite significant progress in nanofabrication technology, the development of SiC on an insulator (SiCOI)-based photonics faces challenges due to fabrication-induced material optical losses and complex processing steps. An alternative approach to mitigate these fabrication challenges is the direct deposition of amorphous SiC on an insulator (a-SiCOI). However, there is a lack of systematic studies aimed at producing high optical quality a-SiC thin films, and correspondingly, on evaluating and determining their optical properties in the telecom range. To this end, we have studied a single-source precursor, 1,3,5-trisilacyclohexane (TSCH, C₃H₁₂Si₃), and chemical vapor deposition (CVD) processes for the deposition of SiC thin films in a low-temperature range (650–800 °C) on a multitude of different substrates. We have successfully demonstrated the fabrication of smooth, uniform, and stoichiometric a-SiCOI thin films of 20 nm to 600 nm with a highly controlled growth rate of ~0.5 Å/s and minimal surface roughness of ~5 Å. Spectroscopic ellipsometry and resonant micro-photoluminescence excitation spectroscopy and mapping reveal a high index of refraction (~2.7) and a minimal absorption coefficient (<200 cm⁻¹) in the telecom C-band, demonstrating the high optical quality of the films. These findings establish a strong foundation for scalable production of high-quality a-SiCOI thin films, enabling their application in advanced chip-scale telecom PIC technologies. Full article

This study investigates the propagation characteristics and field distribution of photonic crystals composed of epsilon-near-zero (ENZ) materials and metal cylinders. The research reveals that the cutoff frequency of the photonic crystal formed by combining metal cylinders with an ENZ background is independent of the volume fraction of the metal cylinders and exhibits a stop-band profile within the measured frequency range. This unique behavior is attributed to the scattering of long-wavelength light when the wavelength approaches the effective wavelength range of the ENZ material. Taking advantage of this feature, the study selectively filters specific wavelength ranges from the mid-frequency band by varying the ratio of cylinder radius to lattice constant (R/a). Decreasing the R/a ratio enables the design of waveguide devices that operate over a broader guided wavelength range within the intermediate-frequency band. The findings emphasize the importance of the interaction between light and ENZ materials in shaping the transmission characteristics of photonic crystal structures. Full article

This study details how 3-(naphthalen-2-yl)-1-phenylprop-2-en-1-one (3NPEO) behaves in terms of photophysics when exposed to different solvents. The solvatochromic effect study reveals significant polarity shifts in the excited states of the 3NPEO compound, likely due to an intramolecular proton transfer mechanism. Measurements of dipole moments provide insight into their resonance structures in both ground and excited states. Electrochemical analysis revealed a reversible redox process, indicating a favorable charge transport potential. HOMO and LUMO energies of the compound were computed via oxidation and reduction potential standards. 3NPEO exhibits optimal one-photon and two-photon absorption characteristics, validating its suitability for visible wavelength laser applications in photonic devices. Furthermore, molecular docking and dynamics simulations demonstrated strong interactions between 3NPEO and the progesterone receptor enzyme, supported by structure–activity relationship (SAR) analyses. In vitro cytotoxicity assays on the MDAMB-231 breast cancer cell line showed moderate tumor cell inhibitory activity. Apoptosis studies confirmed the induction of both early and late apoptosis. These findings suggest that 3NPEO holds promise as a potential anticancer agent targeting the progesterone receptor in breast cancer cells. Overall, the findings highlight the substantial influence of solvent polarity on the photophysical properties and the design of more effective and stable therapeutic agents. Full article

Graphene-based micro-ring modulators are promising candidates for next-generation optical interconnects, offering compact footprints, broadband operation, and CMOS compatibility. However, most demonstrations to date have relied on conventional straight bus coupling geometries, which limit design flexibility and require extremely small coupling gaps to reach critical coupling. This work presents a comprehensive comparative analysis of straight, bent, and racetrack bus geometries in graphene-on-silicon nitride (Si₃N₄) micro-ring modulators operating near 1.31 µm. Based on finite-difference time-domain simulation results, a proposed racetrack-based modulator structure demonstrates that extending the coupling region enables critical coupling at larger gaps—up to 300 nm—while preserving high modulation efficiency. With only 6–12% graphene coverage, this geometry achieves extinction ratios of up to 28 dB and supports electrical bandwidths approaching 90 GHz. Findings from this work highlight a new co-design framework for coupling geometry and graphene coverage, offering a pathway to high-speed and high-modulation-depth graphene photonic modulators suitable for scalable integration in next-generation photonic interconnects devices. Full article

In this study, three alternating donor–acceptor (D–A) type [12]cycloparaphenylene ([12]CPP) derivatives ([12]CPP 1a, 2a, and 3a) were designed through precise molecular engineering, and their multidimensional photophysical responses and chiroptical properties were systematically investigated. The effects of the alternating D–A architecture on electronic structure, excited-state dynamics, and optical behavior were elucidated through density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The results show that the alternating D–A design significantly reduced the HOMO–LUMO energy gap (e.g., 3.11 eV for [12]CPP 2a), enhanced charge transfer characteristics, and induced pronounced red-shifted absorption. The introduction of an imide-based acceptor ([12]CPP 2a) further strengthened the electron push-pull interaction, exhibiting superior performance in two-photon absorption, while the symmetrically multifunctionalized structure ([12]CPP 3a) predominantly exhibited localized excitation with the highest absorption intensity but lacked charge transfer features. Chiral analysis reveals that the alternating D–A architecture modulated the distribution of chiral signals, with [12]CPP 1a displaying a strong Cotton effect in the low-wavelength region. These findings not only provide a theoretical basis for the molecular design of functionalized CPP derivatives, but also lay a solid theoretical foundation for expanding their application potential in optoelectronic devices and chiral functional materials. Full article

In classic all-dielectric one-dimensional photonic crystals, transparent bands exhibit strong angular dispersion. Herein, we realize an angle-dispersion-free near-infrared transparent band in a one-dimensional photonic hypercrystal containing hyperbola-dispersion metamaterials. As the incident angle increases from 0° to 80°, the relative shifts of the wavelengths of four transmittance peaks within the transparent band are smaller than 1.5% and the bandwidth of the transparent band marginally fluctuates from 1098.2 to 1132.5 nm. Particularly, the angle-dispersion-free property of the transparent band is quite robust with respect to the layer thickness disturbance. Our work not only offers a viable method of achieving angle-dispersion-free transparent bands but also facilitates the development of transparency-based optical devices. Full article

An optical power splitter (OPS) with arbitrary splitting ratios has attracted significant research interest for its broad applications in photonic integrated circuits. A series of OPSs with arbitrary splitting ratios based on silicon nitride (Si₃N₄) platforms are presented. The devices are designed with ultra-compact dimensions using three-dimensional finite-difference time-domain (3D FDTD) analysis and an inverse design algorithm. Within a 50 nm bandwidth (1525 nm to 1575 nm), we demonstrated a 1 × 2 OPS with splitting ratios of 1:1, 1:1.5, and 1:2; a 1 × 3 OPS with ratios of 1:2:1 and 2:1:2; and a 1 × 4 OPS with ratios of 1:1:1:1 and 2:1:2:1. The target splitting ratios are achieved by optimizing pixel distributions in the coupling region. The dimensions of the designed devices are 1.96 × 1.96 µm², 2.8 × 2.8 µm², and 2.8 × 4.2 µm², respectively. The designed devices achieve transmission efficiencies exceeding 90% and exhibit excellent power splitting ratios (PSRs). Full article

Hierarchical surface structuring is a critical aspect of advanced materials design, impacting fields ranging from optics to biomimetics. Among several laser-based methods for complex structuring of photo-responsive surfaces, the broadband vectorial interferometry proposed here offers unique performances. Such a method leverages a polychromatic laser source, an unconventional choice for holographic encoding, to achieve deterministic multiscale surface structuring through interference light patterning. Azopolymer films are used as photosensitive substrates. By exploring the interaction between optomechanical stress modulations at different spatial periodicities induced within the polymer bulk, we demonstrate the emergence of hierarchical Fourier surfaces composed of multiple deterministic levels. These structures range from sub-micrometer to tens of micrometers scale, exhibiting a high degree of control over their morphology. The experimental findings reveal that the optical encoding scheme significantly influences the resulting topographies. The polarization light patterns lead to more regular and symmetric hierarchical structures compared to those obtained with intensity patterns, underscoring the role of vectorial light properties in controlling surface morphologies. The proposed method is fully scalable, compatible with more complex recording schemes (including multi-beam interference), and it is applicable to a wide range of advanced technological fields. These include optics and photonics (diffractive elements, polarimetric devices), biomimetic surfaces, topographical design, information encoding, and anti-counterfeiting, offering a rapid, reliable, and versatile strategy for high-precision surface structuring at a submicrometric scale. Full article

Interest in germanium electronic devices is experiencing a comeback thanks to their suitability for a wide range of new applications, like CMOS transistors, quantum technology or infrared photonics. Among these applications, Ge-based thermophotovoltaic converters could become the backbone of thermo-electrical batteries. However, these devices are still far from the efficiency threshold needed for industrial deployment, with surface recombination as the main limiting factor for the material. In this work, we discuss the main passivation techniques developed for germanium photovoltaic and thermophotovoltaic devices, summarizing their main advantages and disadvantages. The analysis reveals that surface recombination velocities as low as 2.7 cm/s and 1.3 cm/s have already been reported for p-type and n-type germanium, respectively, although improving surface recombination velocities below 100 cm/s would result in marginal efficiency gains. Therefore, the main challenge for the material is not reducing this parameter further but developing robust and reliable processes for integrating the current techniques into functional devices. Full article

InGaN-based photovoltaic devices have attracted great attention due to their remarkable theoretical potential for high efficiency. In this paper, the influence of different distributions of step-gradient indium content within the intrinsic region on the photovoltaic performance of P-I-N type InGaN/GaN solar cells is numerically investigated. Through the comprehensive analysis of carrier dynamics, it is found that for the device with the indium content decreasing stepwise from 50% at the top to 10% at the bottom in intrinsic region, the photovoltaic conversion efficiency is increased to 10.29%, which can be attributed to joint influence of enhanced photon absorption, reduced recombination rate, and optimized carrier transport process. Full article

Enhancing light absorption in two-dimensional (2D) materials, particularly few-layer structures, is critical for advancing optoelectronic devices such as light sources, photodetectors, and sensors. However, conventional absorption enhancement strategies often suffer from unstable resonant wavelengths and low-quality factors (Q-factors) due to the inherent weak light–matter interactions in 2D materials. To address these limitations, we propose an all-dielectric metasurface graphene-perfect absorber based on toroidal dipole bound state in the continuum (TD-BIC) with an ultra-narrow bandwidth and stable resonant wavelength. The proposed structure achieves tunable absorption linewidths spanning three orders of magnitude (6 nm to 0.0076 nm) through critical coupling modulation. Furthermore, the operational wavelength can be flexibly extended to any near-infrared region by adjusting the grating width. This work establishes a novel paradigm for enhancing the absorption of 2D materials in photonic device applications. Full article

Tunneling modes in all-dielectric one-dimensional photonic crystals can be utilized for multi-channel filtering. However, these tunneling modes generally blue shift upon increasing the incident angle. When hyperbolic metamaterials are introduced into one-dimensional photonic crystals, the competition between the propagation phase shifts in the dielectric materials and hyperbolic metamaterials can result in different angle dependencies, including blue shift, abnormal zero shift, and abnormal red shift. When the reduction in the propagation phase in the dielectric layer exceeds the increment in the propagation phase in the hyperbolic metamaterial, the tunneling modes are blue-shifted; conversely, when the phase increment in the hyperbolic metamaterial exceeds the phase reduction in the dielectric layer, the tunneling modes are abnormally red-shifted. When the phase changes in the two materials are the same, the tunneling modes are angle independent. In this study, we investigated the multiple filtering effects of one-dimensional photonic structures composed of hyperbolic metamaterials. These composed structures exhibited multiple tunneling modes based on one-, two-, or three-angle dependencies and can be applied in novel optical devices with different angle-dependence requirements. Full article