Search Results (2,728)

To promote the development of long-distance high-speed underwater optical wireless communication (UWOC) based on visible light, this study proposes a high-bandwidth UWOC system based on micro-light-emitting-diodes (micro-LEDs) adopting the Non-Return-to-Zero On-Off Keying (NRZ-OOK) modulation. The numerical simulations reveal that optimizing the structural parameters of gallium nitride (GaN)-based micro-LED through dimensional scaling and quantum well layer reduction may significantly enhance optoelectronic performance, including modulation bandwidth and luminous efficiency. Moreover, experimental validation demonstrated maximum real-time data rates of 420 Mbps, 290 Mbps, and 250 Mbps at underwater distances of 2.3 m, 6.9 m, and 11.5 m, respectively. Furthermore, the underwater audio communication was successfully implemented at an 11.5 m UWOC distance at an ultra-low level of incoming optical power (12.5 µW) at the photodetector (PD) site. The channel characterization yielded a micro-LED-specific attenuation coefficient of 0.56 dB/m, while parametric analysis revealed wavelength-dependent degradation patterns, exhibiting positive correlations between both attenuation coefficient and bit error rate (BER) with operational wavelength. This study provides valuable insights for optimizing underwater optical systems to enhance real-time environmental monitoring capabilities and strengthen security protocols for subaquatic military communications in the future. Full article

This review summarizes the recent advances in the application of nanomaterial coatings in optical fiber sensors, with a particular focus on deposition techniques and the research progress over the past five years in humidity sensing, gas detection, and biosensing. Benefiting from the high specific surface area, abundant surface active sites, and quantum confinement effects of nanomaterials, advanced thin-film fabrication techniques—including spin coating, dip coating, self-assembly, physical/chemical vapor deposition, atomic layer deposition (ALD), electrochemical deposition (ECD), electron beam evaporation (E-beam evaporation), pulsed laser deposition (PLD) and electrospinning, and other techniques—have been widely employed in the construction of functional layers for optical fiber sensors, significantly enhancing their sensitivity, response speed, and environmental stability. Studies have demonstrated that nanocoatings can achieve high-sensitivity detection of targets such as humidity, volatile organic compounds (VOCs), and biomarkers by enhancing evanescent field coupling and enabling optical effects such as surface plasmon resonance (SPR), localized surface plasmon resonance (LSPR), and lossy mode resonance (LMR). This paper first analyzes the principles and optimization strategies of nanocoating fabrication techniques, then explores the mechanisms by which nanomaterials enhance sensor performance across various application domains, and finally presents future research directions in material performance optimization, cost control, and the development of novel nanocomposites. These insights provide a theoretical foundation for the functional design and practical implementation of nanomaterial-based optical fiber sensors. Full article

This paper presents a hybrid computational architecture for efficient and robust digital transmission inspired by helical genetic structures. The proposed system integrates advanced modulation schemes, such as multi-pulse-position modulation (MPPM), high-order quadrature amplitude modulation (QAM), and chirp spread spectrum (CSS), along with Reed–Solomon error correction and quantum-assisted search, to optimize performance in noisy and non-line-of-sight (NLOS) optical environments, including VLC channels modeled with log-normal fading. Through mathematical modeling and simulation, we demonstrate that the number of helical transmissions required for genome-scale data can be drastically reduced—up to 95% when using parallel strands and high-order modulation. The trade-off between redundancy, spectral efficiency, and error resilience is quantified across several configurations. Furthermore, we compare classical genetic algorithms and Grover’s quantum search algorithm, highlighting the potential of quantum computing in accelerating decision-making and data encoding. These results contribute to the field of operations research and supply chain communication by offering a scalable, energy-efficient framework for data transmission in distributed systems, such as logistics networks, smart sensing platforms, and industrial monitoring systems. The proposed architecture aligns with the goals of advanced computational modeling and optimization in engineering and operations management. Full article

Broadband optical amplifiers operating in the 2 μm spectral region are critical for advancing mid-infrared photonic systems, yet achieving high gain with low noise remains challenging. In this work, we demonstrate a high-performance tapered fiber amplifier incorporating PbS quantum dots (QDs) as the gain medium. By optimizing the tapering geometry and QD doping concentration, we achieve a broadband on-off gain of >15 dB across a 200 nm bandwidth (1900–2100 nm). The unique combination of PbS QDs’ size-tunable bandgap and the tapered fiber’s enhanced evanescent field interaction enables efficient pump-probe overlap, resulting in a broader gain bandwidth compared to conventional rare-earth-doped fiber amplifiers. This work establishes a promising platform for compact, high-bandwidth mid-infrared light sources and amplifiers. Full article

By analyzing atomic force microscopy images, we studied the spatial distribution of nanoholes etched by InAl droplets in In_0.52Al_0.48As surfaces, employing molecular beam epitaxy. We identified two temperature regimes, which exhibit significantly different droplet aggregation behavior. The droplet density shows an exponential decrease with increasing temperature in the low-temperature regime (300–390 °C), which is characterized by an activation energy of 0.34 eV, whereas for the high-temperature regime (435–505 °C), the exponential decrease persists but with a much larger activation energy of 2.20 eV. The increased activation energy is accompanied by a strong elongation of the denuded zone around the nanoholes in the distribution of the nearest neighbors along the [011] direction, whereas the distribution is almost isotropic in the low-temperature regime. In both temperature regimes, we observe a narrowing of the capture-zone size distribution with increasing temperature; however, the distribution broadens with the transition to the high-temperature regime before narrowing again with further increasing temperature. By employing nucleation theory, we find that the critical nucleus size does not appear to be significantly different between the two temperature regimes. However, Ostwald ripening is probably relevant, so nucleation theory does not describe our experiments completely. We propose a change in the surface reconstruction, with a more anisotropic arrangement in the high-temperature regime as the underlying reason for the significantly different behavior in the two regimes. Full article

The implementation of efficient free-space channels is fundamental for both classical and quantum free-space optical (FSO) communication. This can be challenging for fiber-coupled receivers, due to the time variant inhomogeneity of the refractive index that can cause strong fluctuations in the power coupled into the single-mode fiber (SMF), and requires the use of adaptive optics (AO) systems to correct the atmospheric-induced aberrations. In this work, we present two adaptive optic systems, one using a fast-steering prism (FSP) for the correction of tip-tilt and a second one based on a multi-actuator deformable lens (MAL), capable of correcting up to the third order of Zernike’s polynomials. We test both systems at telecom wavelength both with artificial turbulence in the laboratory and on a free-space channel, demonstrating their effectiveness in increasing the fiber coupling efficiency. Full article

Miller’s rule originated as an empirical relation between the nonlinear and linear optical coefficients of materials. It is now accepted as a useful tool for guiding experiments and computational materials discovery, but its theoretical foundation had long been limited to a derivation for the classical Lorentz model with a weak anharmonic perturbation. Recently, we developed a mathematical framework which enabled us to prove that Miller’s rule is equally valid for quantum anharmonic oscillators, despite different dynamics due to zero-point fluctuations and further quantum-mechanical effects. However, our previous derivation applied only to one-dimensional oscillators and to the special case of second- and third-harmonic generation in a monochromatic electric field. Here we extend the proof to three-dimensional quantum anharmonic oscillators and also treat all orders of the nonlinear response to an arbitrary multi-frequency field. This makes the results applicable to a much larger range of physical systems and nonlinear optical processes. The obtained generalized Miller formulae rigorously express all tensor elements of the frequency-dependent nonlinear susceptibilities in terms of the linear susceptibility and thus allow a computationally inexpensive quantitative prediction of arbitrary parametric frequency-mixing processes from a small initial dataset. Full article

This study investigated the optimization of optical film configurations to mitigate angular color deviation—a persistent challenge in quantum dot (QD) backlight displays. A white backlight was implemented by placing a yellow CdSe-based QD film on a blue edge-lit backlight, followed by various combinations of prism and diffusion films. Optical characteristics, including luminance, spectral distribution, and chromaticity coordinates, were systematically measured over a viewing-angle range of −70° to 70° for different film arrangements. Applying one or two prism films significantly enhanced normal luminance and improved color conversion efficiency by forming vertical optical cavities; however, this also introduced the side-lobe phenomenon, leading to color non-uniformity. Placing a diffusion film between the QD and prism films did not resolve these issues, whereas positioning it as the topmost layer above the prism films effectively eliminated color dispersion and produced a uniform luminance distribution. These results provide practical design guidelines for optimizing optical film stacks in QD-enhanced backlight units to achieve superior color uniformity in LCD displays. Full article

We propose a novel method for controlling the frequency of semiconductor lasers. This technique facilitates the production of devices with fast frequency tuning and intrinsic linearization of laser frequency sweeps. The electrical contact layer positioned between the lower undoped cladding and the waveguide, along with the upper laser contact, is used for the optical gain pumping. Since the laser pumping current does not pass through the lower cladding, changes in carrier concentration within the cladding affect the laser frequency while minimally impacting the device’s output power. Control of the free carrier concentration in the lower cladding is achieved using the space-charge-limited current (SCLC) technique. This novel approach establishes a linear relationship between the laser frequency shift (∆f) and voltage (V) applied to the cladding—an essential feature for light detection and ranging (LIDAR) system development. The proposed technique is applicable to all semiconductor lasers. As an example, we present the calculated characteristics of a quantum cascade laser (QCL) operating at a 10 µm wavelength. Full article

This work reports the synthesis and characterization of Carbon Quantum Dots (CQDs) embedded in an organic–inorganic hybrid SiO₂: PMMA matrix, designed as a novel plastic scintillator material. The CQDs were synthesized through a solvo-hydrothermal method and incorporated using a sol–gel polymerization process, resulting in a mechanically durable and optically active hybrid. Structural analysis with X-ray diffraction and TEM confirmed crystalline quantum dots approximately 10 nm in size. Extensive optical characterization, including band gap measurement, photoluminescence under 325 nm UV excitation, lifetime evaluations, and quantum yield measurement, revealed a blue emission centered at 426 nm with a decay time of 3–3.6 ns. The hybrid scintillator was integrated into a compact cosmic ray detector using a photomultiplier tube optimized for 420 nm detection. The system effectively detected secondary atmospheric muons produced by low-energy cosmic rays, validated through the vertical equivalent muon (VEM) technique. These findings highlight the potential of CQD-based hybrid materials for advanced optical sensing and scintillation applications in complex environments, supporting the development of compact and sensitive detection systems. Full article

A new series of luminescent Zn(II) complexes based on mono- and bis-imidazo[1,5-a]pyridine ligands was synthesized to investigate the correlation between structural modifications and photophysical behaviour. Systematic variations in substituent groups, coordination geometry, and π-conjugation extent enabled precise tuning of absorption and emission properties. Spectroscopic analysis revealed that Zn(II) coordination enhances molecular rigidity and induces a conformational change in the ligands, resulting in improved quantum yields (up to 37%) and significant blue shifts in emission. Notably, in bis-ligand systems, each imidazo[1,5-a]pyridine unit retains its distinct emissive signature upon complexation, demonstrating their optical and electronic independence. This modular behaviour confirms that individual emissive centres can be predictably manipulated without mutual interference, offering a powerful design strategy for multichromophoric materials. Structural, vibrational, and mass spectrometric characterizations further corroborate the stability and coordination patterns of the synthesized complexes. These insights lay the groundwork for engineering efficient and tunable Zn(II)-based luminophores for applications in optoelectronics, sensing, and bioimaging. Full article

There has been considerable scientific interest in third-order nonlinear optical materials for photonic applications. In particular, materials exhibiting a strong electronic optical Kerr effect serve as essential components in the ultrafast nonlinear photonic devices and are instrumental in the development of all-optical signal processing technologies. Therefore, the accurate prediction of material-relevant properties, such as second hyperpolarizabilities, remains a key topic in the search for efficient photonic materials. However, the field standards in quantum chemical computation are still inconsistent, as studies often lack a firm statistical foundation. This work presents a comprehensive in silico investigation based on multiple full-factorial experiments, aiming to clarify the strengths and limitations of various computational approaches. Our results indicate that the coupled-cluster approach at the CCSD level in its current response-equation implementations is not yet able to outperform the range-separated hybrid density functionals, such as LC-BLYP(0.33). The exceptional performance of the specifically tailored basis set Sadlej-pVTZ is also described. Not only was the presence of diffuse functions found to be mandatory, but also adding ample polarization functions is shown to be inefficient resource-wise. HF/Sadlej-pVTZ is proven to be reliable enough to use in molecular screening. Meta functionals are confirmed to produce poorly consistent results, and specific guidelines for constructing range-separated functionals for polarizability calculations are drawn out. Additionally, it was shown that many of the contemporary solvation models exhibit significant limitations in accurately capturing nonlinear optical properties. Therefore, further refinement in the current methods is pending. This extends to the statistical description as well: the mean absolute deviation descriptor is found to be deficient in rating various computational methods and should rather be replaced with the parameters of the linear correlation (the slope, the intercept, and the R²). Full article

High-power laser diodes (LDs) inherently generate considerable heat during current loading, which presents substantial challenges to the stable operation of laser systems. This study reports a machine learning-based approach that is to be applied to LD temperature control systems, in which a fuzzy neural network (FNN) algorithm is integrated with a proportional-integral-derivative (PID) controller to create an FNN-PID control architecture. The proposed algorithms synergistically integrate fuzzy rule-based systems with neural network learning frameworks, and, furthermore, facilitate adaptive parameter optimization while preserving the interpretability of the decision-making process. Applying the optimized algorithm temperature controller to the LD with output optical power of 110 W @ 888 nm, compared with the conventional PID, the FNN-PID algorithm has shortened the temperature settling time by 77% during 100 W heat generation in LD, the long-term temperature fluctuation is decreased from ±0.126% to ±0.06%, the corresponding optical power steady-state precision is decreased from ±0.09% to ±0.04%, and the step response time of temperature and corresponding power are reduced by 73.4% and 70% from 25 °C to 27 °C, respectively. The FNN-PID outperforms conventional methods (the PID algorithm and the Fuzzy-PID algorithm) in managing thermal fluctuations, and it offers potential for precise laser control applications to enhance beam quality and stability. Full article

The external cavity frequency doubling technique serves as a potent method for generating short-wavelength lasers, yet achieving high-power outputs remains challenging due to the thermal lens effect. This study systematically investigates the generation mechanism of the thermal lens effect and its impact on laser performance. By optimizing the bow-tie cavity design and leveraging a large beam waist of 106 µm to suppress thermal-induced distortions, we demonstrate a tunable 420 nm laser with up to 800 mW of output power and a peak conversion efficiency of 77%. The fundamental light source, a Ti:Sa laser locked to an ultra-stable cavity, ensures a narrow linewidth, flexible tunability, and long-term frequency stability. This high-performance blue laser enables the efficient Rydberg excitation of rubidium atoms, presenting critical applications in quantum computing, quantum simulation, and quantum precision measurement. Full article

Soft nanocomposites were prepared by dispersing lipophilic carbon quantum dots (CQDs) in the liquid crystal compound 8CB. The quality of the dispersion was evaluated using fluorescence microscopy, while the microstructure of the samples was examined via polarized optical microscopy. We investigated the influence of CQDs on the orientational order parameter S as a function of temperature and sample composition by measuring birefringence. Additionally, the Fréedericksz transition threshold, along with the characteristic response and relaxation times, was measured for each sample as a function of temperature and applied voltage amplitude. The extracted rotational viscosity ${\gamma }_1$ exhibits a pretransitional divergence upon cooling toward the smectic-A phase. Its temperature dependence was analyzed using established models from the literature, and the corresponding activation energy was determined. Notably, our analysis suggests that the presence of CQDs alters the power-law dependence of ${\gamma }_1$ on the orientational order parameter S. The influence of CQDs on the elastic constants has been investigated. Full article