Femtosecond laser focusing within transparent materials enables the fabrication of complex three-dimensional optical waveguide structures, offering broad potential for waveguide lasers and integrated photonic devices. Achieving optical waveguides with high beam quality, low propagation loss, and strong supercontinuum generation is essential for advancing integrated photonic systems. In this work, we design and fabricate a parabolically tapered concentric annular waveguide (Hereinafter collectively referred to as parabolically tapered waveguide) inside a sapphire crystal using femtosecond laser direct writing. The fabricated structure exhibits a large input radius and a small output radius. At an output radius of 4 mu m, a low propagation loss of 0.505 dB (at 632.8 nm) and a near-diffraction-limited beam quality (M2 = 1.06) are achieved. Under 1030 nm fs laser excitation, the designed structure exhibits supercontinuum broadening with a -20 dB bandwidth of 84.9 nm, which is significantly wider than that of the depressed cladding waveguide (59.1 nm) and the bulk material (22.9 nm). These results highlight the advantages of parabolically tapered waveguides in optical field confinement and nonlinear enhancement, providing a valuable strategy for the development of high-performance threedimensional integrated photonic devices.

All-dielectric metasurfaces have been extensively investigated for their support of both local and nonlocal resonances in optical sensing applications. Typically, traditional sensors based on local resonance suffer from a trade-off between the sensitivity (S) and quality (Q) factor, whereas nonlocal resonance leverages strong interactions between adjacent unit cells to reduce sensing detection limits while enhancing the figure of merit (FOM). Here, we propose and experimentally demonstrate a high-performance optical polarization-independent sensor based on a hexagonal lattice all-dielectric metasurface, which could excite two toroidal dipole (TD) resonances in the near-infrared wavelength range. The nonlocal tuning of TD resonance through parameter space enables the excitation of bound states in the continuum (BIGs) at a short wavelength (theoretical Q-factor of 4.18 & times; 107). Parameter optimization achieves quasi-BIG with strong nonlocal characteristics and a Q-factor of 4373, which is more than 20-fold higher than that of other localized TD resonances experimentally. Simulations and experiments have consistently demonstrated that nonlocal resonance significantly outperforms local resonance in refractive index (RI) sensing, owing to its superior lateral control of the electric field via nonlocal leakage modes. This work proposes an effective method to address the trade-off between the S and Q-factor in traditional sensors by utilizing nonlocal leakage modes, while also demonstrating a positive correlation between sensor performance and nonlocality. To our knowledge, this work represents the highest experimental S (1480 nm/RIU) and FOM (4228 RIU-1) values reported for RI sensing by utilizing leaky modes in nonlocal metasurfaces. The sensor provides theoretical and experimental support for integrated highly sensitive optical sensors. (c) 2026 Chinese Laser Press

Laser wire directed energy deposition (LWDED) has garnered significant attention for the fabrication of large metallic components. However, the complex coupling effects among its process parameters pose challenges for porosity control. Optimizing parameter combinations to effectively minimize porosity is therefore critical to the broader adoption of this technology. In this study, systematic experiments and modeling were conducted to optimize the LWDED process parameters and predict porosity. First, single-factor and orthogonal experiments were performed to evaluate the individual effects of laser power, scanning speed, wire feeding speed, and air pressure on porosity. Subsequently, range analysis and analysis of variance were employed to determine the influence of each parameter and the significance of their interactions. Four machine learning models-SVR, RF, GPR, and XGBoost-were then trained and compared. Among them, the SVR model exhibited the best predictive performance, achieving an R2 of 0.8960, an RMSE of 0.19, and an MAE of 0.15, outperforming the other three models. Based on this, the SVR model was further utilized to establish the mapping between process parameters and porosity. Contour maps and three-dimensional surface plots were generated to visualize porosity variation patterns under interacting parameters. Validation experiments showed that the maximum relative error between model predictions and experimental measurements was 0.514%, with an average error of 0.251%. This study provides a reliable reference for selecting low-porosity parameter combinations in the LWDED fabrication of 5356 aluminum alloy components.

Supercontinuum generation is a key technology in nonlinear optics, supporting a wide range of applications in frequency metrology and spectroscopy. Integrated photonics offers a promising route toward compact and efficient supercontinuum sources, yet extending the bandwidth while maintaining high spectral flatness remains a central challenge. Here we demonstrate an integrated broadband supercontinuum source based on segment-chirped periodically poled lithium niobate (SC-PPLN) nanophotonic waveguides. By discretizing the chirped poling profile into independently optimized segments, this approach enables high-fidelity ferroelectric domain inversion with near-ideal duty cycles and establishes broadband quasi-phase matching, overcoming the domain inhomogeneity and efficiency limitations commonly encountered in conventional chirped poling. The engineered phase-matching landscape supports efficient wavelength conversion and simultaneous activation of multiple second- and third-order nonlinear processes. Experimentally, we achieve a spectrally flat supercontinuum spanning three optical octaves, from 320 nm in the ultraviolet to 2600 nm in the mid-infrared. These results establish segment-chirped poling as a practical strategy for broadband wavelength conversion and supercontinuum generation in integrated photonics.

The computational infrared speckle wavemeter features a compact structure and high resolution but typically relies on InGaAs cameras for speckle pattern recording. Compared to silicon-based cameras, InGaAs cameras are significantly more expensive and less sensitive, limiting their practical applications. While second-harmonic generation (SHG) can shift infrared light into a wavelength range detectable by silicon-based cameras, its conversion efficiency drops sharply at low input power, resulting in weak signals and reduced detection performance. To overcome these limitations, we propose a wavemeter scheme based on sum-frequency generation (SFG) in a thin-film lithium niobate waveguide. This approach enables efficient infrared-to-visible conversion, enhancing detection sensitivity under weak-light conditions. At an input power of 1.0 mW, spectral line reconstruction with a 5 pm resolution is achieved using the transmission matrix method. Furthermore, by incorporating a ResNet-50 neural network, the system achieves a recognition accuracy exceeding 96.5% even at an input power as low as 0.5 mW, with 1 pm wavelength spacing. The proposed method offers a low-cost, high-sensitivity, and compact solution for near-infrared weak-light detection, expanding the applicability of speckle-based computational wavemeters in practical scenarios.

We demonstrate the generation of dissipative soliton resonance (DSR) in a passively mode-locked fiber laser utilizing the nonlinear polarization rotation effect induced by a helical small-period long-period fiber grating (HSP-LPG). The HSP-LPG, fabricated via femtosecond laser direct writing technology, has a period of 30 mu m and a length of 6 mm. It exhibits polarization-dependent loss values of dB at 1464.70 nm, 14.23 dB at 1518.00 nm and 22.05 dB at 1572.40 nm, respectively, which have effectively facilitated the achievement of stable mode locking. Through careful adjustment of the polarization controller, a dissipative soliton resonance was achieved with a SNR of 61.50 dB. As the pump power increases, the pulse width of the DSR increases from 15.70 ns to 37.70 ns. To analyze how resonator parameters affect the evolution of DSR pulses, an improved genetic algorithm is employed to systematically explore their impact mechanism. It turns out that the formation of DSR square pulses is directly determined by pump power, saturation energy, and phase delay angle. This work indicates that the polarization-dependent helical grating serves as an excellent polarizer applicable in ultrafast fiber laser, contributing to a more profound comprehension of the pulse dynamics operating within the DSR operating region.

The limited gain bandwidth of the gain medium constrains pulse duration and peak power of femtosecond lasers, presenting significant challenges in strong-field physics and ultrafast material processing. Here, we introduce a nonlinear pulse post-compression (NLPC) scheme utilizing three-dimensional tapered waveguides (3D-TWs), directly inscribed inside sapphire via an ultrafast laser. The tapered geometry significantly enhances nonlinear interactions and promotes mode selection, leading to efficient spectral broadening. Coupled with grating-based dispersion compensation, this approach compresses 581 fs pulses down to 84 fs, increases peak power by a factor of four, and improves beam quality to near-diffraction-limited conditions (M2 = 1.02). The results conceptually verify the feasibility of employing femtosecond-laser-inscribed 3D waveguides for pulse compression, indicating preliminary potential for pulse shortening and peak-power enhancement and offers insights for developing integrated pulse compression schemes in crystal waveguides.

Photonic-crystal surface-emitting lasers (PCSELs) are a new type of semiconductor laser with the potential for high-power output and high-beam-quality operation. Integrating a distributed Bragg reflector (DBR) into PCSELs can significantly enhance device performance. However, the growth of high-aluminum-content DBRs on photonic crystal layers with buried air holes presents two major challenges. First, the low mobility of aluminum atoms increases the propagation of surface roughness from the substrate into the DBR, increasing defect density. Second, the high growth temperatures required for DBR growth can deform the thermally unstable air holes. In this work, we investigated a metal–organic chemical vapor deposition (MOCVD) regrowth process for fabricating DBRs on PCSELs. By adjusting the epitaxial growth temperature and V/III ratio, we effectively controlled the diffusion of adatoms on both the sample surface and inside the holes. As a result, the root mean square (RMS) surface roughness decreased by ~96%, and uniform buried air holes were obtained, with a filling factor of ~ 18.8% and a depth of ~ 270 nm, without significant deformation. Finally, we fabricated a PCSEL device with a DBR structure, exhibiting a beam divergence angle of ~ 0.5° and a peak power of about 0.86 W. This study provides a key process solution for the development of PCSELs with high-quality DBR structures, enabling further improvement in optical output performance.

Optoelectronic devices are extensively studied in the fields of computing and memory. Two-dimensional ferroelectrics present an attractive platform for ultrathin integrations with enhanced functionality. This study reports an optoelectronic synapse based on a PtSe2/α-In2Se3/MoS2 ferroelectric heterojunction that exhibits high-performance multistate memory and artificial synaptic behavior through effective modulation of ferroelectric polarization via electric-field-induced polarization and amplified light-induced depolarization effects. By strategically incorporating two active interfaces into the double heterojunction, the light-induced depolarization effect is remarkably amplified. This enables time-resolved encoded pulse recognition beyond spatial or intensity resolution. The device recognizes up to 8 time-sequence-encoded pulse states from "000" to "111", with each state distinguished by over 500 pA. It also effectively emulates synaptic short-term plasticity and long-term potentiation during "Learning" and "Forgetting" processes, with tunable parameters such as light wavelength, power, and pulse number controlling the response. This device offers a promising approach to designing 2D ferroelectric heterojunctions for optoelectronic neuromorphic applications.

K9 glass is prone to developing color center defects under gamma irradiation, which exhibit strong absorption at specific laser wavelengths. However, most of these color centers exhibit an annealing phenomenon in natural environmental conditions, wherein their absorptive characteristics gradually diminish or even disappear. Hence, this study proposes employing a high-temperature accelerated annealing approach to address the color centers induced in K9 glass by gamma irradiation, aiming to attain stable absorption characteristics for specific wavelengths. Initially, experiments were conducted to generate color centers in K9 glass using gamma irradiation to investigate the influence of different irradiation doses on the optical absorption characteristics of K9 glass. Subsequently, the gamma-irradiated K9 glass was subjected to natural annealing at room temperature, wherein the unstable color centers exhibited a slow recovery process during annealing. Building upon this, high-temperature annealing was employed to expedite the recovery of unstable color centers in darkened K9 glass. Finally, a comprehensive analysis of the mechanisms behind gamma irradiation and high-temperature annealing in K9 glass was conducted using various material characterization techniques. The research findings hold significant importance for efficiently obtaining K9 glass with stable absorption at specific wavelengths, thereby further enhancing the optical performance of K9 glass in extreme environments.

Fringe projection profilometry (FPP) is a widely employed technique owing to its rapid speed and high accuracy. However, when FPP is utilized to measure shiny surfaces, the fringes tend to be saturated or too dark, which significantly compromises the accuracy of the 3D measurement. To overcome this challenge, this paper proposes an efficient method for the 3D measurement of shiny surfaces based on FPP. Firstly, polarizers are employed to alleviate fringe saturation by leveraging the polarization property of specular reflection. Although polarizers reduce fringe intensity, a deep learning method is utilized to enhance the quality of fringes, especially in low-contrast regions, thereby improving measurement accuracy. Furthermore, to accelerate measurement efficiency, a dual-frequency complementary decoding method is introduced, requiring only two auxiliary fringes for accurate fringe order determination, thereby achieving high-efficiency and high-dynamic-range 3D measurement. The effectiveness and feasibility of the proposed method are validated through a series of experimental results.

Supercontinuum generation (SCG) in crystal is of great value in ultrafast and nonlinear optics. The stability of the long-term operation of SCG is crucial, and it requires a deeper understanding of the evolution of SCG over time. In this study, the evolution of SCG over time in sapphire under varying pump pulse energy was explored in detail, revealing its recoverability. Experimental results show that SC degradation and recovery are primarily affected by the accumulation of defects inside the material and the temperature fluctuations. By controlling the temperature of the sapphire, we succeeded in dramatically extending the stabilization duration of SCG under high-repetition-rate ultrashort laser pulses from a few minutes to several tens of minutes. This finding highlights the crucial role of temperature management in stabilizing SC and provides valuable insights for achieving longer and more stable SC output in future practical applications.

Icing phenomena present significant challenges across various industrial and daily applications. Superhydrophobic surfaces in the Cassie - Baxter (CB) state are widely recognized as an effective passive anti-icing strategy. However, the inherent instability of the CB metastable states under cryogenic conditions poses a significant challenge to the practical implementation of superhydrophobic surfaces in passive anti-icing systems. To overcome this limitation and enhance the stability of the CB state, a dual-period stabilized micro-nano structure (DPMNS) has been developed through a dual-beam femtosecond laser processing strategy on aluminum alloy surface. By precisely controlling the energy ratio and temporal delay between laser pulses, we achieved programmable fabrication of hierarchical surface architectures. A systematic analysis reveals that the depth ratio (R = h1/h2) between primary and secondary structures enhances the solid-liquid interfacial energy barrier. This enhanced energy barrier effectively suppress the transition from the CB state to the Wenzel state, as evidenced by low-temperature contact angle measurements. Through these optimizations, we achieved a static icing time of 476 s at -15 degrees C. Compared to single-period micro-nano structures, the icing delay time increased by 56.6 %. Furthermore, compared to structures fabricated by single-beam processing, the icing delay time improved by 271.9 %, representing a remarkable 43.3-fold increase over an untreated aluminum alloy surface. To evaluate the robustness of the structures, rigorous testing procedures were conducted, including saltwater immersion, hightemperature exposure, high-speed water flow impact, and sandpaper abrasion. The results consistently demonstrated superior anti-icing performance of the DPMNS compared to single-period structures under repeated tests. This laser-based hierarchical structuring approach provides a scalable and durable solution for combating ice accretion in aerospace, energy infrastructure, and cryogenic applications.

Black phosphorus (BP) is a promising two-dimensional (2D) material with extraordinary optical anisotropic properties in the near-infrared region (NIR). It is widely exploited in NIR photodetecting, NIR imaging, and NIR polarization detecting. Despite its superior anisotropy, the polarized response is still limited to several layers. We present a polarization-enhanced black phosphorus photodetector based on a nonlocal metasurface. Benefiting from enhanced light–BP interaction, the device responsivity is improved by 7 times over that of non-enhancement. At zero bias, our device has a responsivity of 9.13 mA/W with 1514 nm incidence. Our photodetector performs an ability to enhance the selective polarization photoresponse of BP armchair direction or zigzag directions by changing the BP placement. Enhanced by polarization sensitive resonance, the cross polarization response ratio (PR) increases from ∼2.3 to ∼13.1. Our results indicate that the device has potential for NIR polarization imaging and polarization multiplexing detecting areas.

Dispersion compensating fibers (DCFs) have a main role in compensating for residual dispersion. Their tiny core sets them apart from standard fibers. Construction of low-loss, all-fiber DCF architectures is essential to meet a variety of application requirements with conventional single-mode fiber (SMF). A highly efficient and reliable method is adopted to obtain a low-loss connection between DCF and SMF by a femtosecond laser direct-writing technology, thus it can enable the mode-field distribution and mode area of a DCF to be precisely controlled to match those of the SMF. The optimization loss of 3.28 dB in the fusion splice endpoint from SMF to DCF is obtained by adopting this method. We have also verified theoretically and experimentally the process parameters which affect the splicing loss, namely length, diameter, and pulse energy. Further, the mode-field adapter of SMF/DCF/SMF has been applied in normal dispersion mode-locked fiber lasers, which generates a dissipative soliton with a central wavelength of 1558.00 nm and a 3 dB-bandwidth of 20 nm. The laser can operate stably with a signal-to-noise ratio of 62 dB. Our method provides a simpler, more reliable and novel way to prepare mode-field adapters.

Accurate identification of light wavelengths with high spectral resolution is crucial for precision measurements, bio-imaging, metrology, and various other applications. In speckle-based wavelength recognition systems using multimode fibers (MMFs), spectral resolution can be enhanced by increasing the fiber length. However, longer fibers compromise system stability and reliability. In this paper, we propose a speckle-based wavelength recognition technique that employs defect-engineered multimode fibers prepared with a femtosecond laser. Our method introduces random defect arrays within standard multimode fibers to excite additional higher-order modes, thereby significantly improving spectral resolution. Specifically, incorporating 30 random defect arrays into a 5 cm multimode fiber results in a spectral resolution enhancement from approximately 250 pm to 100 pm. Further, integrating this technique with neural networks enables the classification of light into three bands (1500 nm, 1550 nm, and 1600 nm) with a prediction accuracy exceeding 99% on a dataset with 20 pm intervals. The fibers utilized in this study are characterized by their short length, compact size, stability, and ease of operation, making them well-suited for integration into miniaturized devices. The defect-engineered multimode fiber approach offers novel insights into highly integrated and reliable wavelength recognition systems.

Titanium dioxide (TiO2) exhibits exceptional photocatalytic activity and holds considerable potential for degrading organic pollutants. However, optimizing its fabrication to meet the growing demands for efficient pollutant degradation remains a critical challenge. This study explores a novel approach combining femtosecond laser processing in burst mode with anodization to enhance the growth of anatase-phase TiO2. Hierarchical TiO2 nanostructures were fabricated on a titanium (Ti) surface, followed by the formation of well-ordered TiO2 nanotubes (TNTs) through anodization and annealing. Photocatalytic degradation tests using methylene blue (MB) solution revealed a 13% improvement in efficiency for burst-mode-treated samples compared to single-pulse laser processing and a 26% enhancement over samples subjected only to anodization and annealing. This approach not only advances microstructural processing and surface modification techniques but also demonstrates significant potential for enhancing the photocatalytic performance of TiO2, paving the way for more effective pollutant degradation applications.

The acoustic signals generated during the laser paint removal process contain valuable information that reflects the state of paint removal. However, it is often overshadowed by complex environmental noise, posing significant challenges for real-time monitoring of paint removal based on acoustic signals. This paper introduces a real-time acoustic monitoring method for laser paint removal using deep learning techniques for the first time. Initially, the original acoustic signals from both clean and unclean paint removal processes are collected and denoised to extract time-domain, frequency-domain, and time-frequency-domain features. The mel frequency cepstral coefficients (MFCC) from the time-frequency domain are then used as inputs to train a convolutional neural network (CNN). The trained CNN model achieves a real-time discrimination accuracy of 97% and an AUC-ROC score of 99%, outperforming classical deep learning models of back propagation neural network (BP), support vector machine (SVM), and recurrent feedforward neural network (RF) that use time and frequency domain features as input. Furthermore, a real-time paint removal monitoring system based on this CNN model was developed, utilizing the NVIDIA Jetson Nano as the core controller. The system demonstrated continuous monitoring capabilities over a period of 1 hour, with a single judgment time of about 60 ms and an accuracy of 94.3%, thereby achieving real-time online monitoring.

The fiber Bragg grating (FBG) is fabricated by the femtosecond laser writing technique with a plane-by-plane (Pl-by-Pl) method in the double-cladding fiber (DCF). The refractive index modified (RIM) region formed by this method is 12 μm × 8 μm in size. Due to the Pl-by-Pl method, high-order Bragg resonances with reflectance greater than 99% can be achieved. The fabricated high-quality FBG features a narrow full width at 3 dB bandwidth of approximately 0.45 nm, a high reflectivity above 99%, and almost no side-mode peaks. To investigate the application of fabricated FBGs, we have built a thulium-doped all-fiber oscillator with purely forward-pumped structures. A thulium-doped fiber laser (TDFL) at a central wavelength of 1953.79 nm was constructed by using the prepared fiber grating. The signal-to-noise ratio (SNR) is above 56 dB. When the pump power is 19 W, the total output power of the continuous wave is 4 W, and the output efficiency is 25.6%. In addition, the numerical calculation has been carried out to further optimize the output power. This work provides a possible approach for designing and implementing a continuous Tm-doped fiber laser with enhanced output efficiency.