Multimode fibers are promising for compact imaging and spectroscopy. However, current implementations are typically limited to a single function and often lack robustness against environmental disturbances. Unlike approaches that solely analyze the fiber end-face, we exploit the high information density of the leaky field from a fiber taper. A lensless system with a deep learning framework is developed, simultaneously capturing multi-modal data from the taper leaky field and the end-face speckle. This approach achieves spectral reconstruction with a resolution of 0.05 nm and enables high-quality image recovery. By fusing both light fields, we significantly enhance image quality (MNIST SSIM up to 0.99), demonstrating a robust, all-fiber platform for integrated spectroscopic and imaging applications. (c) 2026 Chinese Laser Press

We report a narrow-linewidth Er/Yb co-doped fiber (EYDF) amplifier tunable from 1570 to 1610 nm with an output power exceeding 330 W and a 3 dB linewidth below 150 pm. It is the highest, to the best of our knowledge, output power for the 1.5 μm-band tunable fiber lasers to date. The maximum output power reached 450 W with the optical efficiency of 35.3% when operating at 1570 nm. The main amplifier was in-band pumped by 1535 nm fiber lasers to avoid 1 μm-band amplified spontaneous emission (ASE). A piece of EYDF was inserted before the main amplifier to filter out the 1.5 μm-band ASE that originated from the pre-amplifiers, which permitted a powerful amplification for all tunable wavelengths without ASE damage. We demonstrated a robust approach for achieving high-power, tunable, narrow-linewidth 1.5 μm-band fiber lasers with high ASE suppression ratios.

Spectral beam combining is an effective approach to overcome the single-fiber output power limitation of fiber lasers. For spectral beam combining systems, high-performance narrow-linewidth fiber laser sources play a crucial role in determining the output power, combining efficiency, beam quality, thermal management, and compactness. In spectral beam combining systems, a widely adopted scheme for narrow-linewidth fiber lasers is to broaden the spectrum of a single-frequency seed through phase modulation, followed by power amplification of the phase-modulated seed. This approach offers strong capability in spectral control while maintaining a narrow linewidth. In this work, the modulation waveform is optimized to reduce the spectral power density. In addition, a low-NA large-mode-area gain fiber is adopted in the main amplifier stage to further mitigate stimulated Brillouin scattering. Experimentally, a 5 GHz-level narrow-linewidth fiber laser with an output power of 3 kW is achieved. The beam quality reaches M2 = 1.26/1.21, and no transverse mode instability is observed. To the best of our knowledge, this represents the highest output power reported for a 5 GHz-level narrow-linewidth fiber laser within the full gain bandwidth of ytterbium-doped fiber. The results of this work are expected to provide a higher performance laser source for spectral beam combining systems.

We report a dual-wavelength pumped narrow-linewidth Er/Yb co-doped fiber (EYDF) amplifier with a record output power of 721 W at 1568 nm. The main amplifier was pumped by 1018 nm and 1535 nm fiber lasers. At the maximum output power, the 3-dB linewidth was 107 pm, and the optical efficiency was 30.2%. No slope-efficiency roll-off was observed at the highest power level, indicating that further power scaling is feasible. This work demonstrates an effective pumping scheme for power scaling of EYDF amplifiers.

Deep learning (DL) has been applied to phase control in coherent beam combining (CBC) recently. However, existing DL-based approaches for filled-aperture CBC essentially convert the phase-locking path into tiled-aperture schemes. Consequently, common-path phase locking in DL-based filled-aperture CBC remains unrealized. Common-path refers to a phase-locking scheme in which the phase information is extracted from the combined beam after the same combining system. In this paper, a common-path phase-locking method is proposed. By exploiting the intrinsic nonuniformity, each laser source is effectively labeled, enabling a mapping between the combined speckle and the multi-source phase. A neural network is employed to reconstruct the phase. Simulations with 25-channel CBC demonstrate a phase-locking accuracy of up to lambda/39. Notably, it remains effective under dynamic phase disturbances. Our work presents a common-path phase-locking approach based on a neural network for filled-aperture CBC, which can offer a new solution for the field.

This paper proposes an energy-managed spatiotemporal mode-locked (STML) fiber laser, in which the potential enhancement in soliton energy and intriguing spatiotemporal dynamics of solitons are explored. In STML lasers, counteracting modal dispersion is crucial for achieving stable STML solitons. Here, we demonstrate that the energy-managed mechanism is capable of restraining intermodal walk-off in a walk-off-sensitive anomalous-dispersion STML laser. The walk-off suppression not only occurs at an intentionally introduced spectral filter but also in multimode fibers because of enhancing intermodal spatiotemporal interaction for suppressing inter-modal dispersion. In the cavity, the effects of filter bandwidth and mode excitation on walk-off suppression are investigated. Experimentally, thanks to the energy management, pulses with 8.9 nJ energy and 5.58 ps duration are achieved from the STML fiber laser. Via adopting a narrower filter and a lower repetition rate, a single-pulse energy of 16.4 nJ is obtained, which represents nearly twofold energy improvement over the previous report in all-fiber STML lasers at the 1.5 mu m band, to the best of our knowledge. This approach not only facilitates high-energy pulse generation but also provides insights into suppressing intermodal walk-off in STML fiber lasers. (c) 2026 Chinese Laser Press

Temporal solitons arise from the balance of dispersion and nonlinearity. Recent advances have extended beyond conventional second-order dispersion solitons, demonstrating that pure high-even-order dispersion solitons (PHEODSs), which emerge from the interplay of negative even-order dispersion and nonlinearity, possess superior energy-scaling capabilities. Multimode fiber lasers, with their rich spatiotemporal degrees of freedom, provide an ideal platform for investigating PHEODS dynamics. In this work, we numerically characterize the properties and diverse nonlinear phenomena of PHEODSs in multimode fiber lasers. We demonstrate bi-stability in a multimode cavity and uncover a direct transition to chaos via soliton explosion, bypassing conventional intermediate pulsating states. Furthermore, we identify a novel pulsating regime that simultaneously exhibits chaotic dynamics and dual-period pulsation, revealing a distinct instability pathway for PHEODSs. These insights deepen the understanding of novel dynamical evolution of PHEODS under non-equilibrium conditions.

High-precision metrology has laid the foundation for semiconductor fabrication and life sciences. However, existing displacement measurement approaches are incapable of performing flexible probing within complex equipment interiors. Here, we present a in situ, non-contact nano-displacement measurement approach. Leveraging a multimode fiber probe empowered by deep learning, fine feature information can be efficiently extracted from superoscillatory speckles, achieving single-ended detection with 10 nm resolution and 99.95% accuracy. A physical model is established to correlate the displacement with higher-order modes proportion in the fiber. Sub-millimeter-sized probe enables detecting targets with different structures in confined spaces. Robust recognition is achieved through joint learning, under varying fiber bending conditions and different metal materials. With extreme compression ratios of less than 0.1%, the system delivers high accuracy, low training costs, and high-speed processing. The imaging capability of the probe is also experimentally validated, proving potential as a powerful tool in applications such as lithography, weak force sensing, and super-resolution micro-endoscopy.

The evolution of soft robots into embodied intelligent systems relies fundamentally on precise proprioception. However, a universal solution for capturing continuous deformations during diverse interactions, particularly in spatially confined interventional scenarios, remains lacking. Here, we introduce a deep learning-enabled versatile shape perception method based on a single-ended multimode fiber (MMF). By leveraging the intrinsic integration advantages of optics, our minimalist reflective architecture physically eliminates the dependence on complex demodulation units and distal devices. Furthermore, treating chaotic optical speckle fields as data streams encoding high-dimensional shape information, reconfigurable neural decoders resolve a single physical channel into versatile perception modes tailored to heterogeneous tasks: discrete state confirmation on soft grippers (>99% accuracy), continuous shape tracking on bionic dexterous hands (~5-fold spatial resolution enhancement), and intuitive 3D morphological reconstruction of soft surgical robots (IoU>0.93). Overall, our work establishes a versatile framework for breaking hardware adaptability limits via computation, laying a solid foundation for closed-loop control in digital twins of soft robots.

Pure-quartic solitons (PQSs) provide a promising route toward high-energy pulse generation through the balance between fourth-order dispersion (FOD) and Kerr nonlinearity. Compared with single-mode fiber lasers, multimode cavities introduce intermodal coupling, providing rich spatiotemporal degrees of freedom for exploring high-dimensional PQS dynamics. However, the influence of spectral filtering on these multimode dynamics remains largely unexplored. Here, we numerically characterize the properties and diverse nonlinear phenomena of PQSs in a multimode fiber laser by exploring a parameter space spanning the filter profile, filter bandwidth, gain, and FOD. Notably, we demonstrate breathing PQS molecules with multiple pulsating periods. With other parameters fixed, increasing the magnitude of FOD destabilizes the molecular state and promotes explosion events. Furthermore, super-Gaussian filtering enables reentrant stabilization from chaotic evolution to a stable PQS molecule. These results highlight the important role of spectral filtering in multimode PQS fiber lasers and provide an effective approach for stabilizing and regulating complex spatiotemporal dynamics.

In this paper, a 439 W, 1567 nm, narrow-linewidth Er/Yb co-doped fiber (EYDF) laser system pumped by 1018 nm fiber lasers is demonstrated. The 1018 nm fiber lasers are utilized as pumping source to suppress the similar to 1 mu m amplified spontaneous emission. It is the highest output power reported for EYDF lasers to date. A novel EYDF model considering the pair-induced quenching (PIQ) and the excited state absorption (ESA) of Er ions is built to predict the experiment more accurately. Simulation results reveal that ESA and PIQ both contribute to the decline of laser efficiency. Moreover, the scheme of the main amplifier is optimized theoretically based on the model to reach higher output power.

Harnessing multimode nonlinear pulse amplification is an effective way to generate pulses that have broader spectra, shorter durations, and higher energies. Yet, as energy levels increase, a formidable challenge arises—spatiotemporal deterioration (STD), which compromises beam and compression quality. To address these issues, this study examines the effects of co-pumping, counter-pumping, and bidirectional pumping on STD in a double-cladding, large-mode-area Yb-doped nonlinear pulse amplifier. Grounded in a rigorous theoretical framework, we introduce advanced simulation methods and present a novel spatiotemporal quality factor to evaluate modal pulse performance. Our findings highlight a significant difference in amplification dynamics: co-pumping promotes gain-managed nonlinear amplification which extends the spectrum beyond the gain bandwidth but results in considerable STD and increased pedestal energy—limitations that ultimately restrict peak power. Conversely, counter-pumping enables self-similar amplification, a method that is more resilient to STD, leading to enhanced beam quality and higher peak power after compression. By deepening our understanding of nonlinear pulse dynamics, this research contributes to the theory and design principles of high-energy ultrafast fiber amplifiers.

Image transmission through multimode fibers (MMFs) poses a complex inversion challenge due to the intricate light transport and potential information loss. While recent advances in deep neural networks (DNNs) have shown promise in modeling the MMF input‐output relationship, commonly‐used networks such as fully connected (FC) models and convolutional neural networks (CNNs) fall short of leveraging the inherent sparsity of MMF systems, which leads to learning inefficiency and poor angular generalization. Here, an ultra‐compact Radon transform‐facilitated cross‐domain learning framework, called Radon Transmission network (RTMnet), is presented. Inspired by the physical sparsity in MMF's rotational memory effect, the Radon transform is applied to the captured speckle and performs physics‐guided learning of MMF image transmission in the sinogram domain. RTMnet enables high‐fidelity MMF image transmission with an order‐of‐magnitude reduction in computational demand compared to traditional DNN models. Arbitrarily rotated handwritten digit images can be faithfully reconstructed using a limited training data of only 7000 non‐rotated digits. This enhancement in learning efficiency underscores RTMnet's physics consistency and its potential to effectively generalize in resource‐constrained fiber‐based applications such as miniaturized endoscopy systems.

Chirp tuning of ultrashort pulses is crucial for nonlinear fiber amplification and nonlinear dynamics investigations. Here we demonstrate all-fiber chirp tuning via a chirped fiber Bragg grating (CFBG) pair. Two identically long CFBGs were placed reversely to cancel out most of their huge dispersion (∼40 ps/nm or ∼22.4 ps2 @1030 nm), while the controllable temperature gradient along them could be used for precise chirp tuning with a tuning range of ∼ps2, verified by dispersion measurement and ultrashort pulse broadening. This relatively large chirp tuning could be used in prechirp management in nonlinear fiber amplifiers, exemplified by the optical spectrum tailoring therein. In addition, we also show this precise chirp tuning capability could be very helpful for pulse temporal quality diagnosis, which is indispensable for seed pulse optimization. We believe this all-fiber chirp tuning technique would find wide applications in nonlinear amplification and ultrafast nonlinear dynamics investigations.

This publisher’s note corrects content in Appl. Opt. 64 , 8551 ( 2025 ) APOPAI 0003-6935 10.1364/AO.568420 .

Laser beam combining techniques, such as coherent and spectral beam combination, are effective strategies for the further power scaling of fiber lasers. In practical applications, beam quality and polarization extinction ratio (PER) of the narrow-linewidth fiber laser sources can significantly affect the performance of the combining system, including the combining efficiency, beam quality, and thermal regulation. In this paper, a narrowlinewidth linearly polarized fiber laser with high-purity single-mode output and high PER is demonstrated. A theoretical model for the optimization of our amplifier is firstly constructed, considering mode coupling and thermal-induced polarization coupling. Expression of the birefringence employed here is the recently corrected stress-induced birefringence. With this model, we optimize the numerical aperture, bending radius and coiling configurations of gain fiber for suppressing mode coupling and polarization coupling. In experiment, we achieve a 3.116 kW linearly polarized narrow-linewidth fiber laser with the beam quality of Mx2 = 1.09/My2 = 1.06 and a PER of 22.1 dB at maximum power. The thresholds for transverse mode instability, stimulated Brillouin scattering, and self-pulsing are not reached. This work provides an effective design method for high-performance narrow-linewidth linearly polarized fiber lasers. To the best of our knowledge, our results represent the highest level of both beam quality and PER achieved for narrow-linewidth linearly polarized fiber lasers at this power level.

Skyrmions, as topologically structured light fields, have attracted considerable attention due to their unique topological properties and potential applications such as optical communication and advanced sensing technologies. However, their longitudinal evolution, as a dimension ripe for exploitation, typically remains uncontrolled and non-deterministic, hindering its in-depth exploration and application scenarios. Here, this paper presents a novel method using dielectric metasurfaces for precisely modeling the longitudinal dynamics evolution of skyrmions. We introduce a new mechanism that allows for the accurate period modulation of skyrmions stokes properties along the propagation direction by controlling the differences in numerical apertures of a zero-order right-circularly polarized beam and a first-order left-circularly polarized beam. Crucially, the evolution period can be arbitrarily designed, and the propagation distance can be expanded by increasing the waist radius of input beams. To validate this approach, we showcase this paradigm through displacement sensing applications, where single-snapshot polarization measurements directly infer absolute position within a compact metasurface-integrated platform, offering a compact and simple alternative to conventional scanning-based approaches for displacement sensing. Our approach advances the understanding of dynamically controlled topological light fields and enables compact devices for precision metrology and optical information technologies.

This article establishes a model for analyzing polarization extinction ratio (PER) characteristics of high-power linearly polarized fiber lasers. By combining thermal-induced polarization coupling with mode coupling, the distribution characteristics of PER along the fiber are calculated, and the main physical factors affecting PER are summarized. The model is employed to analyze the correlations between PER and the fiber length, bending radius, as well as pumping scheme of the main amplifier in the linearly polarized fiber laser. Subsequently, the experimental testing examined the impact of coiling shape on PER. Finally, a high-power linearly polarized fiber laser based on an oscillator is constructed using optimized parameters, producing an output power of 3 kW and a PER of 20.8 dB.

To scatter the residual pump light that is not fully absorbed and the signal light leaking into the cladding due to factors such as bending, splicing, and other factors, a segmented cladding light stripper (CLS) was fabricated using CO2 laser ablation. A three-segment CLS with a total length of 9 cm was developed. Integrated into a test system, the CLS demonstrated a stripping ratio of 30.9 dB, with an output power of only 0.593 W under an injected pump power of 734 W. Without active cooling, the maximum temperature of the CLS remained below 52.1°C, exhibiting uniform thermal distribution, no significant hotspots, and stable operation. By integrating a laser-ablated cladding light stripper into a 2014 W laser system, exceptional cladding light stripping performance was achieved. Comparative experiments with a corrosion cladding light stripper revealed no significant difference in the system's output power. These results collectively demonstrate that the laser-ablated cladding light stripper is practically applicable to high-power fiber laser systems, with high stripping efficiency.

We report a 544 W, 1568 nm, Er/Yb fiber amplifier dual-wavelength pumped by 1018 nm and 1535 nm fiber lasers.