Search Results (162)

In airborne LiDAR measurements of shallow water bathymetry, conventional data processing often overlooks the radiative losses associated with multiple scattering events, affecting detection accuracy. This study presents a Monte Carlo-based approach to construct a mathematical model that accurately characterizes the multiple returns in airborne laser bathymetric systems. The model enables rapid simulation of laser propagation through water, accounting for multiple scattering events. Based on the Beer–Lambert law and incorporating the parameters of typical Jerlov 1 clear coastal water, the proposed model achieves a seamless integration of the H-G phase function with a Monte Carlo random process, enabling accurate simulation and validation of pulse temporal broadening in waters with varying optical transparency. Unlike most existing studies, which primarily focus on modeling the laser emission process, this work introduces a novel perspective by analyzing the probability of light reception in LiDAR return signals, offering a more comprehensive understanding of signal attenuation and detection performance in underwater environments. The results demonstrate that, for detecting underwater targets at depths of 10 m, considering three or more scattering events improves the accuracy by ~7%. For detecting underwater targets at depths of 50 m, considering three or more scattering events improves the accuracy by 15~33%. These findings can help enhance the detection accuracy and efficiency of experimental systems. Full article

Accurate visual inspection of underwater infrastructure, such as bridge piers and retaining walls, is often hindered by severe image degradation due to light attenuation and scattering. This paper introduces an unsupervised enhancement framework tailored for restoring underwater images containing structural cracks. The method combines a physical modeling of underwater light transmission with a deep image translation architecture that operates without requiring paired training samples. To address the loss of fine structural details, this paper incorporates a multi-scale feature integration module and a region-focused discriminator that jointly guide the enhancement process. Moreover, a physics-guided loss formulation is designed to promote optical consistency and texture fidelity during training. The proposed approach is validated on a real-world dataset collected from submerged structures under varying turbidity and illumination levels. Both objective evaluations and visual results show substantial improvements over baseline models, with better preservation of crack boundaries and overall visual quality. This work provides a robust solution for preprocessing underwater imagery in structural inspection tasks. Full article

Purpose: A novel enhanced monofocal intraocular lens (IOL) has been developed to improve functional intermediate vision, maintaining a distance vision comparable to a standard monofocal lens and avoiding the drawbacks of multifocal IOLs. The aim of this study is to perform optical bench analysis and to evaluate refractive and visual outcomes and patient satisfaction. Methods: This prospective comparative single-center study was conducted in Careggi Hospital, University of Florence (Italy). We included 100 eyes from 50 patients who underwent bilateral cataract surgery. One group received the standard monofocal Tecnis GCB00 IOL, while the other group received the novel enhanced monofocal Evolux IOL. We evaluated binocular visual and refractive outcomes at 6 months after surgery. Binocular defocus curves and contrast sensitivity (CS) were also assessed. Optical quality was also analyzed in terms of higher-order aberrations (HOAs), modulation transfer function (MTF), objective scatter index (OSI), Strehl ratio, effective lens position (ELP), and halo analysis. A Patient-Reported Spectacle Independence Questionnaire (PRSIQ) was performed to assess spectacle independence outcomes. Finally, we analyzed the optical bench of both lenses. Results: All eyes implanted with Evolux achieved excellent distance vision, comparable to that achieved with GCB00. Evolux showed better intermediate and near vision, without any loss of visual quality, contrast sensitivity, or the presence of halos and photic phenomena. The optical bench analysis confirmed the different optical properties of the two lenses and supported the behavior obtained with the clinical defocus curve. Conclusions: These preliminary results show good refractive accuracy and visual outcomes for the enhanced monofocal IOL Evolux after cataract surgery. Further studies are needed to confirm our findings in terms of the number of patients and the period of follow-up. Full article

In this paper, the optical properties and lattice thermal conductivity of Ti₂AlB₂ were studied by first-principles calculations. The real part of the dielectric constant, ε₁, attains a significant value of 47.26 at 0.12 eV, indicating strong polarization capabilities and energy storage capacity. Regarding optical properties, Ti₂AlB₂ exhibits significant absorption peaks at photon energies of 4.19 eV, 6.78 eV, and 10.61 eV, and 14.32 eV, with absorption coefficients of 184,168.1 cm⁻¹, 228,860.8 cm⁻¹, 366,350.8 and 303,440.6 cm⁻¹, indicating a strong absorption capacity. The loss function exhibits peaks at 19.80 eV and the refractive index reaches a maximum of 8.30 at 0.01 eV. Reflectivity is notably higher in the 0–5 eV range, exceeding 44%, which demonstrates excellent reflective properties. This suggests that Ti₂AlB₂ has potential as an optical coating material across certain frequency bands. The lattice thermal conductivity of Ti₂AlB₂ is obtained at 27.2 W/(m·K). The phonon relaxation time is greater in the low-frequency region, suggesting that phonons have a longer duration of action during the heat transport process, which may contribute to higher thermal conductivity. Although the phonon group velocity is generally low, several factors influence thermal conductivity, including phonon relaxation time and Grüneisen parameters. The high Grüneisen parameter of Ti₂AlB₂ indicates strong anharmonic vibrations, which may enhance phonon scattering and consequently reduce thermal conductivity. However, Ti₂AlB₂ still exhibits some lattice thermal conductivity, suggesting that the contributions of phonon relaxation time and group velocity to its thermal conductivity may be more significant. The unique optical properties and thermal conductivity of Ti₂AlB₂ indicate its potential applications in optical coatings and high-temperature structural materials. Full article

Noble metal nanostructures have garnered significant attention for their exceptional optical properties, particularly Localized Surface Plasmon Resonance (LSPR), which enables pronounced near-field electromagnetic enhancements. Among these, bowtie nanoantennas (BNAs) are distinguished by their intense plasmonic coupling within nanogap regions, making them highly effective for applications such as surface-enhanced Raman scattering (SERS). However, the practical utility of conventional BNAs is often hindered by small hotspot areas and significant scattering losses at their peak near-field enhancement wavelengths. To overcome these limitations, we have designed a novel notch metal-insulator-metal bowtie nanoantenna (NMIM-BNA) structure. This innovative design integrates dielectric materials with Ag-BNA nanostructures and strategically positions arrays of silver (Ag) nanorods within the central nanogap. By coupling the larger NMIM-BNA framework with these smaller Ag nanorod arrays, higher-order plasmon modes (often referred to as dark modes) are effectively excited. Consequently, the NMIM-BNA exhibits substantial electric field enhancement, particularly at the Fano dip wavelength, arising from the efficient coupling of these higher-order plasmon modes with dipole plasmon modes. Compared to conventional Ag-BNA nanoantennas, our NMIM-BNA provides a significantly larger hotspot region and an enhanced near-field amplification factor, underscoring its strong potential for advanced SERS applications. Full article

The refractive index is an important optical property of materials which can be used to understand the composition of materials. Therefore, refractive index sensing plays a vital role in biological diagnosis and therapy, material analysis, (bio)chemical sensing, and environmental monitoring. Conventional optical refractive index sensors based on optical fibers and ridge waveguides have relatively large sizes of a few millimeters, making them unsuitable for on-chip integration. Photonic crystals (PCs) have been used to significantly improve the compactness of refractive index sensors for on-chip integration. However, PC structures suffer from defect-introduced strong scattering, resulting in low transmittance, particularly at sharp bends. Valley photonic crystals (VPCs) can realize defect-immune unidirectional transmission of topological edge states, effectively reducing the scattering loss and increasing the transmittance. However, optical refractive index sensors based on VPC structures have not been demonstrated. This paper proposes a refractive index sensor based on a VPC Mach–Zehnder interferometer (MZI) structure with a high forward transmittance of 0.91 and a sensitivity of 1534%/RIU at the sensing wavelength of λ = 1533.97 nm within the index range from 1.0 to 2.0, which is higher than most demonstrated optical refractive index sensors in the field. The sensor has an ultracompact footprint of 9.26 μm × 7.99 μm. The design can be fabricated by complementary metal–oxide semiconductor (CMOS) fabrication technologies. Therefore, it will find broad applications in biology, material science, and medical science. Full article

In future hybrid fiber and radio access networks, wavelength division multiplexing passive optical networks (WDM-PON) based fifth-generation (5G) fronthaul systems are anticipated to coexist with current protocols, potentially leading to non-linearity impairment due to stimulated Raman scattering (SRS). To meet the loss budget requirements of 5G fronthaul networks, this paper investigates the power changes induced by SRS in WDM-PON based 5G fronthaul systems. The study examines wavelength allocation schemes utilizing both the C-band and O-band, with modulation formats including non-return-to-zero (NRZ), optical double-binary (ODB), and four-level pulse amplitude modulation (PAM4). Simulation results indicate that SRS non-linearity impairment causes a power depletion of 1.3 dB in the 20 km C-band link scenario, regardless of whether the modulation formats are 25 Gb/s or 50 Gb/s NRZ, ODB, and PAM4, indicating that the SRS-induced power changes are largely independent of both modulation formats and modulation rates. This effect occurs when only the upstream and downstream wavelengths of the 5G fronthaul are broadcast. However, when the 5G fronthaul wavelengths coexist with previous protocols, the maximum power depletion increases significantly to 10.1 dB. In the O-band scenario, the SRS-induced maximum power depletion reaches 1.5 dB with NRZ, ODB, and PAM4 modulation formats at both 25 Gb/s and 50 Gb/s. Based on these analyses, the SRS non-linearity impairment shall be fully considered when planning the wavelengths for 5G fronthaul transmission. Full article

The 2 μm wavelength is ideal for light detection and ranging and gas sensing due to its eye-safe operation, strong molecular absorption targeting, and low atmospheric scattering—critical for environmental monitoring and free-space communications. The existing 2 μm systems rely on mechanical beam steering, which limits speed and reliability. Integrated photonic solutions have not yet been demonstrated in this wavelength. We propose a focal plane array design to address these challenges. Compared to optical phased arrays requiring complex phase control for each antenna, FPAs have a simple switch-based control and high suppression of background noise. Although FPAs need an external lens for beam collimation, they significantly reduce system complexity. This study introduces a compact, low-loss 1 × 8 focal plane array operating in the 2 μm range, employing a cascaded Mach–Zehnder interferometer switch array on a silicon nitride platform. The device demonstrates a field of view of 16.8°, background suppression better than 17 dB, and excess loss of −1.4 dB. This integrated photonic beam steering solution offers a highly promising, cost-effective approach for rapid beam switching. This integrated photonic beam steering solution offers a highly promising, cost-effective approach for rapid beam switching. Full article

This study explores the biosynthesis, characterization, and evaluation of silver nanoparticles coated with chitosan (AgChNPs) for liquid nanocomposite and biofilm formation in integrated pest management (IPM). AgChNPs were synthesized using Galega officinalis leaf extract as a reducing agent, with varying chitosan concentrations (0.5%, 1%, and 2%) and pH levels (3, 4, and 5). Synthesis was optimized based on nanoparticle size, stability, and polydispersity index (PDI) over 21 days. Biofilms incorporating AgChNPs were analyzed for chemical, physical, mechanical, and thermal properties via Ultraviolet-visible spectroscopy (UV-vis), Dynamic Light Scattering (DLS), Zeta Potential Analysis, Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Transmission Electron Microscopy with Energy Dispersive X-ray Spectroscopy (TEM-EDX), and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) to quantify silver ionization. TEM confirmed spherical nanoparticles (5.54–61.46 nm), and FTIR validated G. officinalis functionalization on chitosan. AgChNPs with 1% chitosan at pH 4 exhibited optimal properties: a size of 207.88 nm, a zeta potential of +42.30 mV, and a PDI of 0.62. Biofilms displayed tunable mechanical strength, with a tensile strength of 3.48 MPa using 5% glycerol and 2% chitosan and an elongation at break of 24.99 mm. TGA showed a two-step degradation process (98.19% mass loss). Ag ionization was 62.57 mg/L in the liquid nanocomposite and 184.07 mg/kg in the biofilms. These findings highlight AgChNPs’ potential for controlled-release properties and enhanced mechanical performance, supporting sustainable agricultural applications. Full article

Fluorescence enhancement technologies play a crucial role in biological and chemical sensors. Currently, effective fluorescence sensors primarily rely on noble metals and high-index dielectric nanostructures. While effective, they are plagued by optical losses and complex fabrication processes. In contrast, low-index material nanostructures offer significant advantages, including the absence of optical losses, ease of fabrication, and cost-effectiveness, but they face the challenge of weaker electric field enhancement. Here, we designed a low-index, randomly oriented polyvinyl acetate (PVAc) nanofiber sensor via scalable electrospinning, enabling multiple scattering within the disordered nanofibers and resulting in an impressive surface-enhanced fluorescence factor of 1170. This sensor achieves a detection limit for rhodamine 6G as low as 7.24 fM, outperforming the reported fluorescence biosensors. Further results of photoluminescence decay dynamics and random lasing validate the effectiveness of multiple scattering in enhancing fluorescence within the polymer nanofiber sensor. With its excellent performance and scalable production process, this randomly oriented, low-index polymer nanofiber sensor offers a promising new pathway for efficient surface-enhanced fluorescence based on multiple scattering. Furthermore, PVAc nanofibers can be extended to other low-index materials capable of forming randomly oriented nanostructures, offering significant potential for cost-effective, high-performance fluorescence sensor applications. Full article

Target strength (TS) is an important design factor for improving the survivability of an underwater vehicle, and various efforts are ongoing to enhance it. Among the design techniques to improve TS, absorbing materials attached to the surface of an underwater vehicle can play a key role by reducing the reflected and scattered acoustic waves. In this study, the acoustic performance of target strength absorbing materials (TSAMs) is first analyzed, and then the simplified procedure of TS analysis considering TSAMs is suggested. The 4-microphone method and transfer matrix method evaluating equivalent material properties of TSAMs are derived, and their effectiveness is cross-validated through a series of analyses for a multi-layer acoustic absorbing structure. From the observed results, it is concluded that the transfer matrix method is more suitable for practical TS analysis than the 4-microphone method because of the relatively low calculation and time costs required for the acoustic performance evaluations of TSAMs. In addition, a simplified TS analysis procedure considering the echo reduction (ER) and transmission loss (TL) is proposed based on the combining method of physical optics and geometric optics (PO/GO combined method) and equivalent material properties. Using the suggested procedure, a series of TS analyses are performed using the Benchmark Target Strength Simulation (BeTSSi) to validate its applicability and effectiveness. Full article

Minimizing optical losses in resonant cavities is crucial for improving photonic device performance. This study focuses on the development of a simulation tool to analyze scattering losses in Fabry–Pérot interferometers (FPIs), offering precise modeling of waveguide dynamics and contributing to accurate loss predictions across various platforms. Optical cavities often suffer from scattering losses due to surface roughness and material defects. Our approach integrates theoretical models and simulations to quantify these losses, utilizing the FPI as a model system. We identified upper and lower reflectivity thresholds, beyond which accurate measurement of losses becomes unreliable. For reflectivity below a certain threshold, measurement errors arise, while excessively high reflectivity can reduce fringe visibility and introduce detector sensitivity issues. Simulations were used to validate the model’s ability to predict reflectivity and attenuation in waveguides with varying loss levels. The software’s flexibility to adjust transmission parameters for different cavity configurations enhances its utility for a broad range of photonic systems. Our study offers a novel methodology for optical loss analysis, with practical applications in optimizing photonic devices. By providing a reliable tool for precise loss measurement, this work supports advancements in optical technologies, enabling the design of more efficient, high-performance devices across various applications. Full article

In view of the necessity of measuring the air content in oil in two-phase flows in the context of general industry, a review of the most popular methods of measuring the air content in oil was carried out. This review includes an assessment of their advantages and disadvantages and of whether they meet criteria such as the degree of filling, the size and number of bubbles, verification, the absence of additional pressure drops, simplicity, and repeatability. In the review, the following methods were examined: the classic trapping method, a modified trapping method, a trapping method using hydrostatic pressure loss, the pressure loss due to frictional flow resistance, the pressure loss with a rapid increase in diameter, the pressure drop in a Venturi tube, the pressure drop in an orifice, a method using the Coriolis effect, the electrical resistance method, the electrical conductivity method, the electromagnetic method, the electrical capacitance method, the thermal anemometry method, the liquid–solid contact electrification method, the photographic method, holography, light scattering, sound dispersion, the ultrasonic transit-time method, X-ray radiation, gamma radiation, neutron radiation, and fiber-optic methods. Full article

Traditional photonic crystal films are becoming increasingly popular in the fields of smart sensing and optical devices due to their high brightness level, but at the same time there is a lack of color saturation and angle dependence, which seriously affects the application of structural color in visual response and display fields. Here, the optical performance of the photonic crystal films was improved by doping a certain amount of carbon black and carbon quantum dots during the film preparation process. Doping carbon quantum dots can effectively compensate for the optical brightness loss caused by the introduction of black substances by utilizing their self-sustained photoluminescence behavior that matches the photonic bandgap. In addition, the introduction of black nanoparticles can effectively enhance surface-resonant scattering, resulting in low angle-dependent structural colors, further expanding the application of structural color in optical display fields. Full article

Background and Objective: Emerging as a hybrid imaging modality, cone-beam X-ray luminescence computed tomography (CB-XLCT) has been developed using X-ray-excitable nanoparticles. In contrast to conventional bio-optical imaging techniques like bioluminescence tomography (BLT) and fluorescence molecular tomography (FMT), CB-XLCT offers the advantage of greater imaging depth while significantly reducing interference from autofluorescence and background fluorescence, owing to its utilization of X-ray-excited nanoparticles. However, due to the intricate excitation process and extensive light scattering within biological tissues, the inverse problem of CB-XLCT is fundamentally ill-conditioned. Methods: An end-to-end three-dimensional deep encoder-decoder network, termed DeepCB-XLCT, is introduced to improve the quality of CB-XLCT reconstructions. This network directly establishes a nonlinear mapping between the distribution of internal X-ray-excitable nanoparticles and the corresponding boundary fluorescent signals. To improve the fidelity of target shape restoration, the structural similarity loss (SSIM) was incorporated into the objective function of the DeepCB-XLCT network. Additionally, a loss term specifically for target regions was introduced to improve the network’s emphasis on the areas of interest. As a result, the inaccuracies in reconstruction caused by the simplified linear model used in conventional methods can be effectively minimized by the proposed DeepCB-XLCT method. Results and Conclusions: Numerical simulations, phantom experiments, and in vivo experiments with two targets were performed, revealing that the DeepCB-XLCT network enhances reconstruction accuracy regarding contrast-to-noise ratio and shape similarity when compared to traditional methods. In addition, the findings from the XLCT tomographic images involving three targets demonstrate its potential for multi-target CB-XLCT imaging. Full article