Search Results (2,077)

Non-mechanical beam steering technology based on liquid crystal optical switches and liquid crystal polarization gratings holds significant application prospects in fields such as laser communication, radar detection, and optical information processing. Traditional nematic liquid crystal optical switches exhibit slow response speeds, whereas novel ferroelectric liquid crystal optical switches, despite their fast response, are hampered in engineering applications by complex fabrication processes, the large number of devices required for cascading, and substantial module thickness. To address these issues, this paper proposes and demonstrates a fast non-mechanical beam steering scheme by cascading a stressed polymer network liquid crystal (SPNLC) optical switch with a liquid crystal polarization grating. The SPNLC is fabricated by mechanically shearing a polymerized liquid crystal–polymer composite, enabling sub-millisecond response and continuous linear phase modulation without the need for an alignment layer. A 30-μm-thick SPNLC half-wave plate was prepared, which introduces a phase retardation of 3.6 μm under a driving voltage of 300 V, and the rise time and fall time are measured to be approximately 526 μs and 560 μs at a driving voltage of 20 V with a 1 kHz square wave, and 470 μs and 538 μs at 27 V under the same waveform conditions. Cascaded with a passive polarization grating, the waveplate enables fast electrical switching of the beam between the ±1st diffraction orders. Furthermore, a two-dimensional multi-angle beam deflector was constructed based on a supra-binary cascade scheme. Experimental results confirm that the system possesses sub-millisecond response, large phase retardation, continuous tunability, and an alignment-layer-free fabrication process, demonstrating its feasibility for large-range fast beam scanning. Full article

Femtosecond laser processing enables spatially controlled modification of the structure, composition, and functionality of advanced materials through highly localized energy deposition and laser–matter interaction mechanisms. This review discusses the role of ultrafast laser irradiation in the engineering of oxide-based functional systems, including functional oxides, oxide-containing layers, interfaces, and heterogeneous structures whose properties are substantially determined by an oxide component. The mechanisms governing laser-induced oxidation, phase transformation, elemental redistribution, defect generation, and hierarchical micro-/nanostructure formation are considered. Particular attention is given to the ability of femtosecond laser processing to create surfaces with tailored interactions with light, liquids, biological environments, and external stimuli, enabling responsive devices and advanced manufacturing strategies. Laser-modified oxide layers and nanostructured interfaces are analyzed as pathways for controlling surface energy, optical properties, chemical activity, and functional response. The relationship between laser-generated architectures and their applications in sensing, actuation, wetting control, and multifunctional systems is discussed. By connecting ultrafast laser surface engineering with emerging 4D manufacturing concepts, this review highlights femtosecond laser technologies as a versatile platform for designing systems with spatially programmed functionality and, where stimulus-dependent behavior is demonstrated, time-dependent performance. Such approaches provide opportunities for integrating adaptive oxide-based functional systems into advanced manufacturing. Full article

Accurate crack width measurement is essential for the condition assessment of reinforced concrete (RC) bridges, yet most unmanned aerial vehicle (UAV) inspections remain limited to pixel-level observations that cannot be converted into reliable metric units without an external scale reference. This paper presents a lightweight, drone-agnostic UAV-mounted metrology system that enables standards-aligned metric crack width measurement directly from inspection imagery. The payload integrates a focusable diffractive optical element (DOE) red laser that projects a cross pattern of known angular geometry, three TF-Luna time-of-flight (ToF) distance sensors, and an ESP-WROOM-32 microcontroller that provides dual-rate sampling, Bluetooth Low Energy (BLE) streaming, and on-board logging. A two-stage calibration links the synchronized distance measurements to the physical length of the projected cross, yielding an image-specific pixel-to-millimeter scale that is applied to pixel-level crack widths obtained from a vision-based segmentation pipeline. The system is field-deployed on the Puente Huamani Bridge in Pisco, Peru, where measurements of 39 cracks classified under AASHTO MBEI condition states are compared against independent manual measurements by six inspectors. The proposed system reduces measurement variability across all condition states (CS), lowering the average coefficient of variation from 0.36 to 0.10 for fine CS1 cracks, from 0.27 to 0.11 for CS2, and from 0.22 to 0.07 for CS3. Cross-platform adaptability is demonstrated through an additional deployment on a DJI Matrice 350 RTK at the Low Level Bridge in Edmonton, Canada. The results indicate that the system provides a practical, low-cost, and scalable solution for repeatable, standards-aligned UAV-based bridge crack assessment. Full article

The Greater Cape Floristic Region (GCFR) in South Africa is a fire-prone biodiversity hotspot where high species richness, structural complexity, and small plant sizes (0.0001–4 m²) pose substantial challenges for remote sensing-based biodiversity assessment. Spectral similarity among species and the mismatch between plant size and sensor pixel dimensions limit the capacity of current and forthcoming spaceborne systems to resolve individual species and accurately detect plot-level diversity changes. We therefore developed a physics-based simulation framework that couples fynbos trait measurements with radiative transfer modeling in the DIRSIG (Digital Imaging and Remote Sensing Image Generation) environment towards quantifying information loss across spectral and spatial scales and to define theoretical limits for biodiversity monitoring. We constructed a three-dimensional virtual scene of post-fire fynbos communities in Grootbos Private Nature Reserve, integrating high-resolution imagery, terrestrial laser scanning (TLS), and structure-from-motion (SfM)-derived point clouds. Field measurements of mean diameter and percent cover were used to scale vegetation models and constrain species abundance. We distributed plant instances using a blue noise sampling algorithm, guided by density maps derived from unmanned aerial system (UAS) imagery. Species-specific optical properties were parameterized using field-measured reflectance data and the PROSPECT radiative transfer model, while terrain structure was derived from SfM-based digital terrain models. The integrated scene was used to simulate multispectral (DJI Mavic 3 MSI), hyperspectral (AVIRIS-NG), and light detection and ranging (LiDAR) observations. Agreement between simulated outputs were evaluated against corresponding field-acquired datasets using spectral signatures and vegetation indices. This framework enables systematic assessment of sensor specification effects on spectral biodiversity metrics and provides a pathway for evaluating theoretical limits of species discrimination across airborne and satellite platforms. Full article

Visible light communication (VLC) has emerged as a transformative optical wireless technology for sixth-generation (6G) networks, offering license-free spectrum access, inherent electromagnetic-interference immunity, high spatial confinement, and the unique ability to combine high-speed wireless connectivity with solid-state lighting infrastructure. However, the transition from conventional VLC links to practical 6G optical wireless systems requires far more than advanced modulation and signal processing. Future VLC performance will be strongly determined by the co-design of photonic front-ends, including high-speed transmitters, spectrally engineered emitters, reconfigurable optical interfaces, intelligent receivers, and energy-autonomous detection units. This article provides a comprehensive, device-centered review of photonic hardware and artificial intelligence (AI) enablers for next-generation 6G VLC systems. Particular attention is given to micro-LEDs, laser diodes, color-conversion materials, including perovskite quantum dots, advanced photodetectors, imaging receivers, wavelength-shifting fiber receivers, solar-cell-based receivers, optical reconfigurable intelligent surfaces (RISs), metasurfaces, beam-steering components, and optical wireless power transfer. This review discusses how AI can support inverse photonic design, transmitter and receiver calibration, nonlinear impairment mitigation, channel-aware beam control, and energy-aware resource management. Unlike broader VLC surveys that mainly emphasize network architecture, this article provides a device-centered perspective on AI-enabled photonic integration for 6G VLC, supported by a comprehensive survey of recent experimental demonstrations. Key challenges related to bandwidth, optical efficiency, receiver field of view, mobility, safety, standardization, and practical deployment are summarized, followed by a research roadmap for 2025–2032. Full article

Yb³⁺-containing glasses and glass-ceramics are attractive photonic materials because Yb³⁺ can act simultaneously as a near-infrared absorber, an energy-transfer sensitizer, a luminescent center, and a composition-dependent modifier of glass structure and crystallization. This brief review focuses on crystallization from parent glasses to glass-ceramics and examines glass-network chemistry, local Yb³⁺ coordination, phase separation, viscosity, heating rate, treatment temperature, holding time control nucleation, crystal growth, phase selection, rare-earth partitioning, transparency, and optical performance. Representative oxyfluoride, phosphate, oxyapatite, borosilicate, and aluminosilicate systems are compared using thermal analysis, X-ray diffraction, electron microscopy, vibrational spectroscopy, and optical spectroscopy. The available data show that Yb₂O₃ or YbF₃ does not have a universal effect on crystallization: low concentrations can promote fluoride-rich clustering or lower the apparent crystallization barrier, whereas higher concentrations can increase packing density, stabilize the residual glass, change the competitive phase assemblage, or suppress crystallization. Crystallization-enhanced luminescence is most consistently obtained when Yb³⁺ and the activator partition into low-phonon-energy nanocrystals while crystal size and refractive-index mismatch remain sufficiently small to preserve transparency. This review also identifies major reporting gaps, including limited quantification of crystalline fraction, partition coefficients, luminescence lifetime, quantum efficiency, and long-term thermal stability. Practical design guidelines and unresolved questions are proposed to support the rational development of transparent Yb³⁺-containing glass-ceramics for lasers, sensing, optical amplification, and related photonic applications. Full article

For gravitational wave observation, an optical design of the telescope has been implemented to perfectly match the laser interferometry system, and stray light analysis is used to quantify the impact of mirror roughness noise on interferometric measurement sensitivity. An off-axis six-mirror afocal optical design, comprising a parabolic primary, hyperbolic secondary and plane-parabolic collimation group, delivers an optical system with a 400 mm entrance pupil, 100× expansion ratio, and λ/30@1064 nm Root Mean Square (RMS) wavefront quality. To obtain a feasible exit pupil position which can easily integrate the laser interferometer, the theoretical mathematical relationships among the exit pupil position, primary–secondary mirror spacing, and radius of curvature of the secondary mirror and the sixth mirror are derived. Accordingly, the effective exit pupil position is extended to 174 mm to match the laser interferometer. The sixth mirror is the primary source of backscattered light. With the RMS roughness of the primary, secondary, and three folding mirrors set to 6.4 Å, 1.6 Å, and 3.7 Å, respectively, the Point Source Transmittance (PST) value can be kept below 3.6 × 10⁻¹⁰ when the RMS roughness of the sixth mirror is less than 1.1 Å. Tolerance analysis is carried out to obtain the feasible engineering distribution of optical parameters, and the statistical results show that the system RMS wavefront error is smaller than 0.01λ@1064 nm. Full article

A high-stability actively mode-locked fiber laser (AMLFL) is proposed and experimentally demonstrated. This AMLFL is based on a distributed feedback laser diode (DFB-LD) injection locking with Fabry-Perot (F-P) etalon frequency stabilization. In this system, a wavelength modulation method is employed to generate the feedback signal for frequency stabilization. The stabilization mechanism utilizes the linear response characteristic of the first-order derivative of the F-P etalon transmission peak. This achieves wavelength stabilization of the DFB-LD. Subsequently, the stabilized light source is injected into the ring cavity of the AMLFL. The proposed system does not require modification to the existing AMLFL cavity. It also features a simple structure and low implementation cost. Experimental results show that, with frequency stabilization, the wavelength drift of a selected spectral line is reduced to within the 10 pm resolution of the OSA. Meanwhile, the standard deviations of the 5 GHz spectral component power fluctuation and the average output optical pulse power are 0.01 dB and 0.01 dB, respectively. Full article

Diffractive optical elements (DOEs) have become core components for converting Gaussian beams into flat-top beams due to their advantages of flexible design, compact size, and precise control over light field distribution. However, during the fabrication of multi-step DOEs, some processes such as ion beam etching tend to produce etching depth errors, which cause deviations of the surface micro–nano phase structures from the designed values and thus severely degrade the beam shaping performance. This paper proposes a focusing DOE for flat-top beam shaping, which combines the focusing phase with the phase optimized by the weighted constraint iterative algorithm to establish a phase distribution resilient to etching depth errors. Thus, the proposed focusing DOE exhibits significantly improved robustness to etching depth errors and effectively reduces the structural complexity of laser optical systems. Our experimental results show that the designed DOE can stably convert the incident Gaussian beam into flat-top beams within the etching depth error range of ±30 nm, with both the flat-top beam uniformity and diffraction efficiency above 95%, and the maximum tolerable etching depth error reaches ±90 nm. Full article

Accurate detection of atmospheric turbulence intensity is essential for atmospheric optics and laser communication, yet efficient inversion methods remain insufficient. This work explores the feasibility of utilizing Gaussian beams and Gaussian Vortex beams for the inversion of atmospheric turbulence intensity (C_n²). We constructed an SLM-based turbulence simulation platform to generate phase screens with different turbulence intensities and acquire corresponding beam spot datasets. A ConvNeXt-based convolutional neural network is optimized, and its performance is compared with the traditional beam average width fitting method. Furthermore, a novel fusion inversion model is proposed by integrating beam average width parameters and beam spot feature information. Experimental results indicate that, for nine refined C_n² turbulence grades, the optimized CNN achieves an inversion accuracy of 98%, while the beam average width method obtains 84.56% based on Gaussian Vortex beams. In contrast, the corresponding accuracies decreased to 95% and 73.84% when adopting conventional Gaussian beams. Compared with the standalone CNN model, the proposed fusion model achieves absolute accuracy improvements of 7.0% in indoor experiments and 2.0% in outdoor field tests. The results demonstrate that Gaussian Vortex beams combined with beam average width features exhibit superior performance in C_n² inversion. The proposed fusion model presents reliable and promising inversion capability, which provides a feasible technical solution for the design and optimization of atmospheric turbulence monitoring systems. Full article

Existing long-wave infrared (LWIR) BaGa₄Se₇ optical parametric oscillators (BGSe-OPOs) adopt linear-cavity configurations yet struggle to balance high beam quality and high output energy. To overcome this limitation, we report a compact Type I phase-matched ring cavity BGSe-OPO pumped by a 1.06 μm laser. Operating at 8.5 μm, the OPO generates 1.2 mJ single pulses with a peak power of 0.25 MW and an optical-to-optical conversion efficiency of 2%. The estimated beam quality factor M² is 9, representing a threefold enhancement relative to linear-cavity under identical pump conditions. The system features a compact footprint of 400 × 200 mm² and a far-field divergence angle of 4 mrad after 6× beam expansion, enabling practical applications in far-field monitoring. Full article

In this work, we developed a measurement platform that employs high-power LEDs as excitation sources in conjunction with a charge-coupled device to perform spatially resolved photoluminescence (PL) and electroluminescence (EL) mapping of commercial LED chips. Two optical configurations (i.e., normal and oblique incidence) were designed to directly compare PL and EL distributions. Unlike conventional laser-based systems, high-power LEDs provide a cost-effective, compact, and scalable solution for PL mapping and provide a broad area of illumination, making them highly suitable for rapid chip-level inspection with strong potential for future wafer-scale scaling. The PL spectra obtained under high-power LED excitation exhibited strong correspondence with the EL spectra. Spatial mappings revealed key emission features, such as metallic contacts, defect-related spots, and surface contamination. The oblique-collection geometry yielded a more intense PL signal and clearer localized emission variations relative to the normal-collection geometry. These findings demonstrate that high-power LED-based PL mapping represents a practical and noninvasive alternative to EL, providing a reliable and scalable pathway for optical inspection of LED chips in both research and industrial applications. Full article

Laser technology has recently gained renewed interest in hysteroscopic surgery due to advances in fiber-optic delivery systems, device miniaturization, and the growing adoption of office-based procedures. In this context, laser energy represents a potential alternative to conventional mechanical and electrosurgical techniques, particularly in settings where precision and tissue preservation are clinically relevant. This narrative review provides a comprehensive and clinically oriented overview of the role of laser technology in modern hysteroscopy. A literature search was conducted in PubMed, Scopus, and Web of Science up to December 2025, focusing on studies addressing technical aspects, clinical applications, safety, and outpatient feasibility of laser-assisted hysteroscopy. Different laser systems, including Nd:YAG, diode, CO₂, Ho:YAG, and KTP lasers, are discussed in terms of physical properties and tissue interaction. Current clinical applications include the management of intrauterine adhesions, submucous myomas, endometrial polyps, septate uterus, and selected cases of endometrial ablation. Available evidence suggests that modern diode laser platforms are particularly suited for office-based procedures due to their combined cutting and coagulative effects and compatibility with small-caliber hysteroscopes. However, most of the current literature is based on small, heterogeneous studies, and robust comparative data with standard hysteroscopic techniques remain limited. As a result, laser hysteroscopy cannot yet be considered a standard approach across indications. To move beyond a purely technical appraisal, this review also frames laser hysteroscopy as a potential translational platform in which laser–tissue interaction, biomarker-informed patient selection, endometrial repair biology, fertility outcomes, and adhesion-formation mechanisms may be integrated into future functional precision medicine pathways. In conclusion, laser technology represents a promising and evolving tool in operative hysteroscopy, with potential advantages in selected clinical scenarios. Further prospective and comparative studies are required to better define its role and to support its broader integration into routine clinical practice. Full article

We propose and experimentally demonstrate an integrated photonic terahertz (THz) frequency-hopping (FH)/dehopping system using electro-optically wavelength-tunable lasers to enhance physical-layer security in terahertz wireless links. The FH THz signal is generated around the 300 GHz band by photomixing a fixed-wavelength laser and an electro-optically tunable laser, while a synchronized FH local oscillator (LO) signal is generated at the receiver for secure photonic dehopping. By utilizing a waveguide-integrated THz combiner and THz detector, the FH LO remains internally coupled and unexposed to potential eavesdroppers. A signal with a 40 GHz hopping span around the 300 GHz band and a 50 Mhops/s FH rate is dehopped to a 5 GHz intermediate frequency. This system simplifies the receiver complexity while enabling secure, high-speed physical-layer terahertz communications. Full article

Methane is the second most important anthropogenic greenhouse gas after carbon dioxide, and its accurate measurement is essential for climate monitoring. In this work, a laser-locked cavity ring-down spectroscopy (LL-CRDS) system was developed for continuous atmospheric methane measurements. By locking the laser frequency to a longitudinal mode of the optical cavity, long-term wavelength stability was achieved, enabling highly stable methane measurements. Laboratory tests demonstrated a precision of 0.4 ppb at an integration time of 3.6 s, a minimum Allan deviation of 0.3 ppb at 15 s, and long-term stability better than 23 ppb over one month without recalibration. Field measurements with a commercial CRDS analyzer showed excellent agreement, with an average deviation of 1.4 ppb. These results demonstrate the suitability of LL-CRDS for long-term atmospheric methane monitoring requiring high precision and low maintenance. Full article