Search Results (388)

This study examines the influence of key technological parameters—marking speed, raster step (Δx), pulse duration, power density, and effective energy—on the laser marking of copper using Yb-doped fiber and CuBr MOPA lasers. Two experimental setups were used: the fiber laser, with 100 ns and 200 ns pulses, and the CuBr laser with 30 ns pulses. Marking speed ranged from 10 to 80 mm/s, with raster steps from 3 to 20 µm for the fiber laser and 3 to 27 µm for the CuBr laser. The study compares different pulse durations and evaluates the impact of laser wavelength on the marking process. Optimal effective energy ranges were identified: 17.4–43.1 kJ/cm² for the Yb-doped fiber laser and 9.90–43.1 kJ/cm² for the CuBr laser. The originality of this work lies in its direct comparison of Yb-doped fiber and CuBr MOPA lasers for copper marking, alongside the simultaneous optimization of multiple parameters. The study provides novel guidelines for high-contrast copper marking, a material with known laser-processing challenges. The identified optimal energy ranges and process parameters can significantly improve the efficiency and quality of industrial copper marking applications. Full article

Tungsten powder/polytetrafluoroethylene (W/PTFE) composites have the potential to replace traditional metallic materials as casings for controllable power warheads. Under explosive loading, they generate high-density and relatively uniformly distributed metal powder particles, thereby enhancing close-range impact effects while reducing collateral damage. To characterize the material’s response under impact loading, plate impact tests were conducted to investigate the effects of tungsten content (70 wt%, 80 wt%, and 90 wt%) and tungsten particle size (200 μm, 400 μm, and 600 μm) on the impact behavior of the composites. The free surface velocity histories of the target plates were measured using a 37 mm single-stage light gas gun and a full-fiber laser interferometer (DISAR), enabling the determination of the shock velocity–particle velocity relationship to establish the equation of state. Experimental data show a linear relationship between shock velocity and particle velocity, with the 80 wt% and 90 wt% composites exhibiting similar shock velocities. The fitted slope increases from 2.792 to 2.957 as the tungsten mass fraction rises from 70 wt% to 90 wt%. With particle size increasing from 200 μm to 600 μm, the slope decreases from 3.204 to 2.756, while c₀ increases from 224.7 to 633.3. Comparison of the Hugoniot pressure curves of different specimens indicated that tungsten content significantly affects the impact behavior, whereas variations in tungsten particle size have a negligible influence on the Hugoniot pressure. A high tungsten content with small particle size (e.g., 90 wt% with ~200 μm) improves the overall compressive properties of composite materials. Based on the experimental results, a mesoscale finite element model consistent with the tests was developed. The overall error between the numerical simulations and experimental results was less than 5% under various conditions, thereby validating the accuracy of the model. Numerical simulations revealed the coupling mechanism between tungsten particle plastic deformation and matrix flow. The strong rarefaction unloading effect initiated at the composite’s free surface caused matrix spallation and jetting. Multiple wave systems were generated at the composite–copper interface, whose interference and coupling ultimately resulted in a nearly uniform macroscopic pressure field. Full article

Brain natriuretic peptide (BNP) is an important biomarker for the diagnosis and prediction of chronic heart failure (CHF). Aiming at the problems of the low sensitivity and poor portability of traditional BNP detection methods, this study proposes a Surface-enhanced Raman-scattering (SERS) fiber-optic sensor based on a multimode fiber (MMF)–no core fiber (NCF) structure. The sensor achieves BNP detection by significantly amplifying the Raman signal of the toluidine blue (TB) marker through the synergistic effect of NCF’s unique optical transmission modes and localized surface plasmon resonance (LSPR). To optimize the sensor performance, we first investigated the effect of the NCF length on the Raman signal, using Rhodamine 6G (R6G), and determined the optimal structural parameters. Combined with the microfluidic chip integration technology, the antibody–BNP–antibody sandwich structure was adopted, and TB was used as the Raman label to realize the quantitative detection of BNP. Experimental results demonstrate that the detection limit of the sensor is lower than the clinical diagnostic threshold and exhibits stability. The sensor sensitivity can be adjusted by regulating the laser power. With its stability and high portability, this sensor provides a new solution for the early diagnosis of heart failure and demonstrates broad application prospects in biomarker detection. Full article

Anti-resonant hollow-core fibers have exhibited excellent performance in applications such as high-power pulse transmission, network communication, space exploration, and precise sensing. Employing anti-resonant hollow-core fibers instead of light guiding arms for transmitting laser energy at the 2.79 μm band can significantly enhance the flexibility of medical laser handles, reduce system complexity, and increase laser transmission efficiency. Nevertheless, common anti-resonant hollow-core fibers do not have the ability to maintain the polarization state of light during laser transmission, which greatly affects their practical applications. In this paper, we propose a polarization-maintaining anti-resonant hollow-core fiber applicable for transmission at the mid-infrared 2.79 μm band. This fiber features a symmetrical geometric structure and an asymmetric refractive index cladding composed of quartz and a type of mid-infrared glass with a higher refractive index. Through optimizing the fiber structure at the wavelength scale, single-polarization transmission can be achieved at the 2.79 μm wavelength, with a polarization extinction ratio exceeding 1.01 × 10⁵, indicating its stable polarization-maintaining performance. Simultaneously, it possesses low-loss transmission characteristics, with the loss in the x-polarized fundamental mode being less than 9.8 × 10⁻³ dB/m at the 2.79 µm wavelength. This polarization-maintaining anti-resonant hollow-core fiber provides a more reliable option for the light guiding system of the 2.79 μm Er; Cr: YSGG laser therapy device. Full article

In this work, we propose and demonstrate a novel approach to suppressing stimulated Raman scattering in an oscillating–amplifying integrated fiber laser (OAIFL) by changing the spectral bandwidth of the output-coupler fiber Bragg gratings (OC-FBGs). The reflectance bandwidth of the fiber Bragg grating (FBG) in the oscillating section was systematically investigated as a critical parameter for SRS mitigation. Three types of long-period FBGs with distinct reflectance bandwidths (1.2 nm, 1.3 nm, and 2 nm) were comparatively studied as output couplers. The experimental results demonstrated a direct correlation between FBG bandwidth and SRS suppression efficiency, with the configuration of the OC-FBG with a 2 nm bandwidth achieving optimal suppression performance. Concurrently, the output power was enhanced to 5.02 kW with improved power scalability. And excellent beam quality was obtained with M² < 1.3. Remarkably, in the architecture of this laser, increasing the bandwidth of the output couplers in the oscillating section had a relatively minor effect on the optical-to-optical (O-O) efficiency, which reached up to 78%. Additionally, this modification also reduced the 3 dB bandwidth of the laser output, thereby achieving a beam output with enhanced monochromaticity. Full article

We reported on a generation of 27 nm spectral bandwidth, two-port output ultrashort pulses directly from an all-normal-dispersion passively mode-locked Yb-fiber laser. Based on the nonlinear polarization rotation (NPR) mode-locking technique, high pump power and optical devices with high damage thresholds were introduced to achieve broad spectral bandwidth and strong output power. The dual wavelengths were emitted from the clockwise and counterclockwise ports, respectively, and self-started mode-locking was achieved. The bidirectional output laser generates stable pulses with up to 223.5 mW average power at a 46.04 MHz repetition rate, corresponding to a pulse energy of 5 nJ. The bidirectional ultrashort outputs of the laser provide potential applications in supercontinuum generation and medical and biological applications. Full article

The spectral characteristics of pump laser diodes (LDs) introduce significant ambiguity into the performance evaluation of high-power ytterbium-doped fiber lasers (YDFLs), obscuring their intrinsic efficiency and hindering reliable system design. Here, we introduce a rigorous quantitative framework that decouples these pump-induced effects by referencing laser performance to the absorbed, rather than the launched, pump power. Our analysis demonstrates that the widely reported discrepancies in conventional optical-to-optical (OO) and slope efficiencies are governed almost entirely by variations in pump absorption, while the influence of the quantum defect is negligible. This approach provides a robust metric for intrinsic laser performance that is independent of the LD’s spectral properties, proving particularly valuable for systems pumped by non-wavelength-stabilized LDs (nWS-LDs). We uncover a non-monotonic evolution of the unabsorbed residual pump power, revealing that the peak thermal load on system components occurs at an intermediate operational state, not at maximum pump power. This finding challenges conventional thermal management strategies and is critical for ensuring the long-term operational reliability of high-power YDFLs. Full article

We report on the generation of 1300 nm ultrashort laser pulses via the soliton self-frequency shift in a high-nonlinearity fiber, pumped by the 41.9 MHz, 67.9 fs, 1073 nm femtosecond laser emitted from an Yb-doped fiber laser system. A numerical simulation was applied to investigate the spectral broadening process driven by the soliton self-frequency shift with increased pump power. The experimental results are in good agreement with the numerical results, delivering a 33 mW, 57.8 fs 1300 nm Raman soliton filtered by a longpass filter. The impact of the polarization direction of the injected pump laser on the soliton self-frequency shift process was also further investigated. The root means squares of the Yb-doped fiber laser and the nonlinearly spectral broadened laser were 0.19%@1h and 0.23%@1h, respectively. Full article

This study focuses on the analysis of soliton solutions within the framework of the time-fractional cubic–quintic nonlinear Schrödinger equation (TFCQ-NLSE), a powerful model with broad applications in complex physical phenomena such as fiber optic communications, nonlinear optics, optical signal processing, and laser–tissue interactions in medical science. The nonlinear effects exhibited by the model—such as self-focusing, self-phase modulation, and wave mixing—are influenced by the combined impact of the cubic and quintic nonlinear terms. To explore the dynamics of this model, we apply a robust analytical technique known as the sub-ODE method, which reveals a diverse range of soliton structures and offers deep insight into laser pulse interactions. The investigation yields a rich set of explicit soliton solutions, including hyperbolic, rational, singular, bright, Jacobian elliptic, Weierstrass elliptic, and periodic solutions. These waveforms have significant real-world relevance: bright solitons are employed in fiber optic communications for distortion-free long-distance data transmission, while both bright and dark solitons are used in nonlinear optics to study light behavior in media with intensity-dependent refractive indices. Solitons also contribute to advancements in quantum technologies, precision measurement, and fiber laser systems, where hyperbolic and periodic solitons facilitate stable, high-intensity pulse generation. Additionally, in nonlinear acoustics, solitons describe wave propagation in media where amplitude influences wave speed. Overall, this work highlights the theoretical depth and practical utility of soliton dynamics in fractional nonlinear systems. Full article

To enable accurate evaluation of satellite laser communication terminals under solar outage interference, this paper presents the design and implementation of a solar radiation simulation system targeting the 1540–1560 nm communication band. The system reconstructs co-propagating interference conditions through standardized and continuously tunable output, based on high irradiance and spectral uniformity. A compound beam homogenization structure—combining a multimode fiber and an apodizator—achieves 85.8% far-field uniformity over a 200 mm aperture. A power–spectrum co-optimization strategy is introduced for filter design, achieving a spectral matching degree of 78%. The system supports a tunable output from 2.5 to 130 mW with a 50× dynamic range and maintains power control accuracy within ±0.9%. To suppress internal background interference, a BRDF-based optical scattering model is established to trace primary and secondary stray light paths. Simulation results show that by maintaining the surface roughness of key mirrors below 2 nm and incorporating a U-shaped reflective light trap, stray light levels can be reduced to 5.13 × 10⁻¹² W, ensuring stable detection of a 10⁻¹⁰ W signal at a 10:1 signal-to-background ratio. Experimental validation confirms that the system can faithfully reproduce solar outage conditions within a ±3° field of view, achieving consistent performance in spectrum shaping, irradiance uniformity, and background suppression. The proposed platform provides a standardized and practical testbed for ground-based anti-interference assessment of optical communication terminals. Full article

To enable the highly sensitive detection of acetylene (C₂H₂) dissolved in transformer oil, a high-power quartz-enhanced photoacoustic spectroscopy (QEPAS) sensing system is proposed. A standard 32.7 kHz quartz tuning fork (QTF) was employed as an acoustic transducer, coupled with an optimized acoustic resonator to enhance the acoustic signal. The laser power was boosted to 150 mW using a C-band erbium-doped fiber amplifier (EDFA), achieving a detection limit of 469 ppb for C₂H₂ with an integration time of 1 s. The headspace degassing method was utilized to extract dissolved gases from the transformer oil, and the equilibrium process for the release of dissolved C₂H₂ was successfully monitored using the developed high-power QEPAS system. This approach provides reliable technical support for the real-time monitoring of the operational safety of power transformers. Full article

By measuring the transfer function of the single-mode multi-aperture vertical-cavity surface-emitting laser (SM MA VCSEL) transmitting over a long single-mode fiber at 850 nm, we confirm that the chirp of the SM MA VCSEL under study is dominated by transient chirp with an alpha value of −3.81 enabling a 19 GHz bandwidth over 10 km of single-mode fiber. The detailed measurement of the VCSEL with different bias currents also allows us to recover other key characteristics of the VCSEL, thereby enabling us to practically construct the optical eye diagrams that closely match the experimentally measured ones. The link-level transfer function can be obtained using an analytical equation including effects of modal dispersion and laser chirp–chromatic dispersion (CD) interaction for an MMF of a given length and bandwidth grade. The narrow linewidth and chirp characteristics of the SM MA VCSEL enable transmission performance that surpasses that of conventional MM VCSELs, achieving comparable transmission distances at moderate modal bandwidths for OM3 and OM4 fibers and significantly longer reaches when the modal bandwidth is higher. The transmission performance was also confirmed with the modeled eye diagrams using extracted VCSEL parameters. The chirp properties also provide sufficient bandwidth for SM MA VCSEL transmission over kilometer-scale lengths of single-mode fibers at a high data rate of 100G or above with sufficient optical power coupled into the fibers. Advanced transmission distances are possible over multimode and single-mode fibers versus chirp-free devices. Full article

A high-power, narrow-linewidth, all-fiber polarization-maintaining (PM) amplifier has been demonstrated. A lasing power of 5870 W has been delivered in master oscillator power amplifier architecture with cascaded white noise source (WNS) phase modulation and bidirectional pumping schemes. The maximal power was limited by the onset of stimulated Brillouin scattering. At the maximum power operation, the amplifier exhibited a 3 dB spectral linewidth of 0.43 nm with beam quality being M² < 1.33 and polarization extinction ratio (PER) being 16.3 dB. To the best of our knowledge, this represents the highest spectral brightness and PER achieved by PM fiber laser systems around 6 kW-level operation. Full article

The use of analog radio-over-fiber (RoF) systems combined with power-over-fiber (PoF) systems has been proposed in recent years for applications involving remote sensors used in hazardous environments or where electrical wiring may be impractical. This article presents a hybrid architecture topology that combines PoF and RoF, using Raman amplification to obtain RF gain. The first emphasis is placed on the use of two types of high-power laser sources (HPLSs) for the PoF system: a 1480 nm Raman-based HPLS and a 1550 nm HPLS that is based on an erbium-doped fiber amplifier (EDFA). The second emphasis of this paper is on how these two HPLSs simulate Raman scattering (SRS) in the fiber, considering different lengths of SMF 28 for the link. Thus, a comparative analysis is proposed considering the effects induced on the RF signal, mainly focused on its RF power gain ($G_{RF}$), noise figure (NF), and spurious-free dynamic range (SFDR). The obtained results show that the architecture using a PoF system based on the 1550 nm HPLS benefits from a lower noise figure degradation, even when the noise generated by the optical amplification is considered. Full article

Light detection and ranging (LiDAR) sensors are essential for applications where high-resolution distance and velocity measurements are required. In particular, frequency-modulated continuous wave (FMCW) LiDAR, compared with other LiDAR implementations, provides superior receiver sensitivity, enhanced range resolution, and the capability to measure velocity. Integrating LiDARs into electronic and photonic semiconductor chips can lower their cost, size, and power consumption, making them affordable for cost-sensitive applications. Additionally, simple designs are required, such as FMCW signal generation by the direct modulation of the current of a semiconductor laser. However, semiconductor lasers are inherently nonlinear, and the driving waveform needs to be optimized to generate linear FMCW signals. In this paper, we employ pre-distortion techniques to compensate for chirp nonlinearity, achieving frequency nonlinearities of 0.0029% for the down-ramp and the up-ramp at 55 kHz. Experimental results demonstrate a highly accurate LiDAR system with a resolution of under 5 cm, operating over a 210-m range through single-mode fiber, which corresponds to approximately 308 m in free space, towards meeting the requirements for long-range autonomous driving. Full article