Transverse mode instability has become a major bottleneck limiting further power scaling and beam quality in high power fiber laser. This study combines experimental and theoretical approaches to systematically investigate the effect of low temperatures on the transverse mode instability threshold in ytterbium-doped fiber lasers. Experimentally, a customized cooling system was employed to lower the temperature of the ytterbium-doped fiber from 0 degrees C to -60 degrees C. Results indicate that the transverse mode instability threshold increases significantly as the temperature decreases, with a maximum improvement of approximately 30%. Theoretically, based on a thermally-induced mode coupling model, the variations of key parameters such as the thermo-optic coefficient and absorption/emission cross-sections at low temperatures were analyzed. The simulation results show a good agreement with the experimental data, which reveals the physical mechanism behind transverse mode instability suppression: firstly, the reduced temperature mitigates gain saturation, leading to a more uniform axial distribution of the thermal load; secondly, the decrease in the thermo-optic coefficient weakens the refractive index modulation by the temperature field, thereby effectively suppressing intermodal energy transfer. This work provides new experimental evidence and theoretical support for understanding mode instability in fiber lasers under low-temperature conditions.

Fiber lasers are increasingly employed in radiative applications, where maintaining laser performance under irradiation is of great importance. Deuterium (D2) D 2 ) loading has been proven efficient in enhancing the radiation resistance of fibers. Nevertheless, such treatment commonly suffers from gas out-diffusion , the full suppres- sion of radiation-induced darkening has not yet been achieved. In this work, we introduced a pretreatment- - deuterium solution doping technique, which stabilized deuterium within the fiber preform. Combined with D2 2 loading, the laser output power under irradiation remained at its initial level. The solution doping process locked OD groups within the fiber core, suppressing color center formation at the source. Coupled with the dynamic repair function of D2 2 loading, this approach achieved complete suppression of radiation-induced darkening under 200 Gy (Si) gamma-ray irradiation, providing a promising strategy for the development of high- performance radiation-resistant fiber lasers. (c) 2026 Chinese Laser Press

Stimulated Raman Scattering (SRS) is a crucial nonlinear effect that limits the power scaling and spectral stability of high-power fiber lasers, and its threshold characteristics exert a vital influence on the application of laser systems in low-temperature environments. Through the design of two types of fiber lasers, this study investigates the effect of low temperature on both the Raman gain and the SRS threshold in silica optical fibers. In Experiment I, a 70-m-long germanium-doped fiber (GDF) was connected to a self-built fiber amplifier and cooled in a lowtemperature chamber. The experimental results indicate that during the cooling of the GDF from 20 degrees C to -60 degrees C, the spectral intensity of SRS gradually increased at each measured temperature point. Experiment II employed a random Raman fiber laser system based on a 700-m GDF to track the SRS threshold drift under low-temperature conditions, thereby quantitatively establishing the temperature dependence of the SRS threshold. As the ambient temperature decreased from 20 degrees C to -20 degrees C, a continuous reduction in the SRS threshold power was observed, with a total decrease of 23.6%. This work demonstrates experimentally, for the first time, that reducing the cooling temperature enhances the Raman gain in silica optical fibers, thereby providing a theoretical foundation and technical support for the design and optimization of high-power fiber laser systems operating in lowtemperature environments.

Enhancing the operational adaptability and stability of laser systems across diverse environments critically relies on improving their performance over a broad temperature range. This paper presents an ytterbium-doped all-fiber laser oscillator capable of stable operation ranging from –50 °C to 50 °C, consistently delivering a 2kW laser output for 1 minute throughout this temperature range. The beam quality factor (M²) measured at room temperature is 1.30. The laser system demonstrates a power conversion efficiency ranging from 62.0% to 72.8% under wide-temperature operation, with no observed stimulated Raman scattering (SRS) or thermal-induced mode instability (TMI). Furthermore, output power was elevated to 3 kW within a temperature range of –10 °C to 20 °C.

Transverse mode instability (TMI), which arises from nonlinear thermal-optical coupling, imposes a major obstacle to the power scaling in traditional fiber oscillators with single resonant cavity. Herein, we proposed a bidirectional output all-fiber laser oscillator at 1050 nm employing a composite cavity, formed by incorporating a fiber Bragg grating (FBG) within the resonator. Combining theoretical simulation and experimental comparison, we investigated the influence of composite-cavity FBG reflectivity on TMI behaviors through contrast experiments with conventional single-cavity structure. Evidence from experiments indicates that an optimal FBG reflectivity window exists for the composite cavity bidirectional output fiber lasers. Compared to the single-cavity configuration, the optimized composite cavity architecture significantly elevates the TMI threshold under different pumping schemes, with the maximum TMI threshold enhancement of 30.9%, and preserves excellent beam quality (M2 < 1.5) even at an output power level of 5.3 kW. These findings open a new horizon for understanding the mechanism of thermally-induced mode instability, and provide a promising approach for inhibiting TMI effect in high-power bidirectional output fiber laser oscillator.

Objective Bidirectional-output fiber lasers have broad application prospects in industrial, medical, communication and other fields due to their unique features of achieving two laser outputs through a resonant cavity. However, the reported high-power bidirectional-output fiber lasers are mainly concentrated in the conventional wavelength band of 1080 nm. Compared with fiber lasers with conventional wavelengths, short-wavelength fiber lasers with wavelengths less than 1060 nm have a wide demand in fields such as biological imaging, nonlinear frequency conversion, and spectral beam combination. However, they are susceptible to nonlinear effects such as amplified spontaneous emission (ASE) and transverse mode instability (TMI), due to the wider absorption cross-section of short wavelength Yb-ions. Methods In this study, a novel short-wavelength composite cavity bidirectional-output all-fiber laser is constructed and shown in Fig. 1. The laser resonant cavity consists of two output-coupler fiber Bragg gratings (OCFBG-A and OCFBG-B) with reflectivity of approximately 10 degrees o, one fiber Bragg grating (FBG) with a reflectivity of approximately 50 degrees o, and two pieces of ytterbium doped fibers (YDF#1 and YDF#2) with a core/cladding diameter of 20/400 mu m. FBG is placed inside the resonant cavity and fused with YDF#1 and YDF#2 at both ends. The central wavelengths of the OCFBG-A, OCFBG-B and FBG are approximately 1050 nm. Wavelength-locked fiber-pigtailed 976 nm laser diodes (LDs) are utilized as the pump sources, which are injected into the resonant through two (6+1) x1 pump/signal combiners. The signal laser is output through fiber endcaps (QBH-A and QBH-B) with a core diameter of 25 mu m. Results and Discussions When the maximum pump power of 6407 W is injected, the total output power reaches 5489 W, with 2278 W of end A and 3211 W of end B, and the corresponding optical-to-optical conversion efficiency of 85.7%, as shown in Fig. 2(a). Figure 2(b) shows the output spectra at the maximum output powers, indicating the center wavelength is 1050 nm, and the Raman suppression ratios at both ends are--21.9 dB and--20.1 dB, respectively. Figure 2(c) shows the temporal signals and the corresponding Fourier transform spectra recorded from A and B ends, which confirms that there is no sign of TMI during the power scaling. The measured beam quality factors (M2) of both ends at the maximum power are 1.52 and 1.34, respectively [Fig. 2(d)]. Conclusions We propose and demonstrate a novel short-wavelength composite cavity bidirectional-output all-fiber laser, and the near single-mode bidirectional output with a central wavelength of 1050 nm and a total output power of 5.5 kW is achieved. The research results are of great significance for suppressing nonlinear effects and transverse mode instability in short-wavelength fiber lasers and bidirectional-output fiber lasers.

Significance With the development of the semiconductor pump source, the rare-earth doped fiber, and the fiber device manufacturing techniques, the ytterbium-doped all-fiber nanosecond-pulsed lasers have developed unprecedentedly, playing an increasingly important role in scientific research, industrial production, and national defense. The all-fiber nanosecond-pulsed amplifier based on the master oscillator power amplifier (MOPA) structure is currently the mainstream strategy to boost the nanosecond pulse energy, and 100 mJ level pulse energy is now available with the single module nanosecond fiber laser. However, for nanosecond fiber laser systems producing 10 mJ level output pulse energy, which require at least 50 mu m level core diameter as the fundamental support, the laser beam quality typically degrades significantly, far from the high beam quality criterion of M-2<2. These low beam quality fiber lasers are not applicable to high brightness applications, and will be an obstacle to the promotion of laser practical performance. In addition to nonlinear effects such as stimulated Raman scattering (SRS), the excess high-order mode components in large core diameter fibers are the most critical issue to improve the beam quality at high pulse energy output. This paper summarizes the progress of research on all-fiber nanosecond-pulsed lasers based on uniform core diameter fibers and tapered fibers. Furthermore, the technical scheme to realize the all-fiber nanosecond-pulsed laser with synergistic development of pulse energy and beam quality is primarily investigated, in the terms of fiber design and laser system global optimization. Progress With continuous and thorough research on nanosecond-pulsed fiber amplifiers, differentiated by the longitudinal core diameter variability, the gain medium of the MOPA system can be roughly classified into two categories. One is the fiber with a uniform core diameter (hereinafter referred to as uniform fibers), and the other is the fiber with a variable core diameter, that is, the recently proposed tapered fibers. According to their internal structure, uniform fibers include photonic crystal fiber (PCF), chirally-coupled-core (3C) fiber, and large mode area double-clad fiber (LMA-DCF), etc. For PCFs, the unique core diameter-independent and endless single-mode property allows near-diffraction-limited and high pulse energy laser output within PCFs with large core diameters. In 2012, Stutzki et al. reported a 26 mJ, M-2=1.3 nanosecond fiber laser system based on a 135 mu m large-pitch PCF (Fig. 1). Similarly, by properly arranging spirally distributed side cores around the main core, high-performance laser output can also be obtained from 3C fiber-based nanosecond fiber amplifiers. For example, Zhu et al. demonstrated a near single-mode, three-stage MOPA system with a pulse energy of 9.1 mJ by incorporating a 55 mu m 3C fiber as the power amplifier medium (Fig. 2). However, for some objective reasons, such as the difficulty in PCF fusion, 3C fiber fabrication, and applicable fiber pump combiner, all-fiber nanosecond-pulsed lasers based on 3C fibers and PCFs have seldom been reported. In high-energy all-fiber applications, LMA-DCF remains the most commonly used gain medium, and the core diameter is one of the most critical parameters, as it largely determines the laser beam quality and extractable pulse energy. For a MOPA system built with LMA-DCF with a relatively small core diameter at the 30 mu m level, a near single-mode, mJ-level pulsed result can typically be obtained. When the core diameter increases to the 50 mu m level, the theoretical extractable energy reaches the 10 mJ level, but the beam quality degrades correspondingly. In 2013, Malinowski et al. successfully amplified the seed pulse to 10.6 mJ within a 50 mu m step-index gain fiber, resulting in a measured beam quality of M-2=7.3 due to the increased number of supported high-order modes. Moreover, LMA-DCF with larger core diameters will produce higher pulse energies but more degraded beam quality. Pulse energies in the tens of mJ and hundreds of mJ levels have been reported in all-fiber and spatially coupled nanosecond MOPA systems, respectively. Regarding tapered fibers, their longitudinal geometry profiles determine their superior suppression effect on nonlinear effects and stimulated Brillouin scattering (SBS) in particular. This has promoted tapered fiber-based systems focusing mainly on single-frequency, narrow linewidth nanosecond fiber lasers. In these studies, limited by the gain bandwidth, only sub-mJ to mJ-level, near single-mode pulsed lasers can be achieved. For wide-spectrum and high pulse energy research, in 2021, Huang et al. demonstrated an all-fiber nanosecond MOPA system as depicted in Fig. 13, in which the power amplifier medium is a tapered fiber with a tapering ratio of 2 and a large-end core diameter of 62 mu m. A high-performance pulse output with 8.3 mJ pulse energy and beam quality of M-2=3.5 is recorded, which is the highest reported pulse energy in laser systems configured with tapered fibers. Conclusions and Prospects In this paper, we review the current progress in research on high pulse energy all-fiber nanosecond-pulsed amplifiers based on uniform fibers and tapered fibers. The degradation of beam quality at high pulse energy indeed restricts the application expansion of nanosecond lasers. Consequently, the development of all-fiber lasers to synergistically enhance beam quality and pulse energy is of high priority. Based on this, we propose a number of reasonable optimization strategies covering gain fiber design and system configuration. The key issue is to suppress high-order modes in large core diameter gain fibers. In this regard, tapered fibers can effectively reduce interference between modes, which has been proven to be a promising method for future performance improvement of pulsed lasers. In addition, the combination of tapered fiber and the newly emerging oscillating-amplifying integrated configuration contributes to efficient and stable pulsed output. Although the rapid growth of all-fiber nanosecond amplifiers also exposes the challenges ahead, the latest progress in theoretical and technical solutions will further optimize the comprehensive performance of nanosecond lasers. In the future, we believe that all-fiber nanosecond-pulsed lasers will provide more possibilities for widespread applications.

In this study, we present a low-numerical-aperture (NA) confined-doped fiber architecture that synergistically mitigates transverse mode instability (TMI) through combined optical waveguide engineering and spatially tailored gain distribution. The individual and combined benefits of low-NA fiber design and the confined-doped fiber design strategy on TMI mitigation are numerically investigated. Building upon these theoretical analyses, a self-developed fiber, featuring a core/cladding diameter of approximately 26/400 mu m, a core NA of approximately 0.045 and a core doping ratio of approximately 75%, is fabricated. Further experimental validation in a master oscillator power amplifier demonstrates 6.74 kW output power with near-single-mode (M ${}<^>2\sim$ 1.49) beam quality, validating the design's efficacy. This study establishes a novel fiber design paradigm that concurrently addresses TMI mitigation, beam quality maintenance and power scalability, offering a viable pathway toward robust high-power fiber laser sources with near-diffraction-limited beam quality.

Wavelength extension of high-power fiber lasers holds critical importance for spectral combining systems. In this work, we demonstrate a 5.1 kW all-fiber amplifier operating at 1100 nm based on master oscillator power amplifier (MOPA). When designing fiber lasers operating at wavelengths above 1080 nm, effective suppression of stimulated Raman scattering (SRS) and transverse mode instability (TMI) must be prioritized. The length of the ytterbium-doped fiber (YDF) was optimized to mitigate SRS while maintaining high power conversion efficiency. Wavelength-stabilized laser diodes (LDs) at 981 nm were employed to reduce quantum defect and enhance the TMI threshold. By optimizing the trade-off between total pump absorption and SRS intensity, a slope efficiency of 75.7 % and an optical signal-to-noise ratio (OSNR) of 23.5 dB were achieved. At 5100 W, the high beam quality was maintained with M2x/M2y = 2.39/2.33. Experimental results demonstrate that SRS significantly degrades beam quality through spectral broadening and power transfer to Stokes waves. This work establishes an important reference for extending monolithic fiber amplifier wavelengths beyond conventional bands while maintaining multi-kilowatt performance.

Dual-wavelength fiber lasers (DWFL) have tremendous application prospects in industrial processing, electronic countermeasures, biomedicine and so on due to their advantages of flexible dual-wavelength output. In this work, we have constructed a 1 μm dual-wavelength fiber laser based on a cascaded resonant cavity with fiber Bragg gratings (FBGs), and the dual-wavelength laser output at the central wavelengths of 1060 nm and 1080 nm was simultaneously achieved. The laser performance involving output power and spectral evolution of this dual-wavelength fiber laser were carefully compared and investigated under two different cascading configurations, including 1060-1080 and 1080-1060. The experimental results reveal that the 1060-1080 configuration was more favorable for the dual-wavelength fiber lasers to generate high-power and high-spectral-purity dual-wavelength laser compared to the 1080-1060 configuration. Furthermore, based on the 1060-1080 configuration, a continuous-wave dual-wavelength laser output at 1060 nm with 40.43 W and 1080 nm with 302.65 W was simultaneously achieved, with the nonlinear effect suppression over 40 dB at the maximum power. To the best of our knowledge, this is the first demonstration of 1 μm cascaded resonant cavity dual-wavelength fiber laser. This work offers a significant guidance for designing and implementing the high-power compactness dual-wavelength fiber laser within 1 μm spectral region.

Significance Linearly polarized fiber lasers have a wide range of applications in areas such as beam combination and nonlinear frequency conversion. Mode instability, nonlinear effects, and other polarization-dependent factors, however, limit the enhancement in the fiber laser output power and thereby hinder the increase in the output power of linearly polarized lasers. In recent years, theoretical breakthroughs and technological advances in the laser fiber fabrication process alongside nonlinear effect/mode instability effect mitigation methods, and laser cavity design have prompted a rapid progress for high power linearly polarized fiber lasers, resulting in a continuous improvement in their overall performance. This paper aims to present the research results and development of linearly polarized fiber lasers globally from the aspects of laser linewidth, operation waveband, operation regime, and emerging power-scaling methods. An outlook on the development trend of linearly polarized fiber lasers is also discussed. Progress First, general progress in linearly polarized fiber lasers with different linewidths, that is, single-frequency, narrow-linewidth, and conventional fiber lasers, alongside superfluorescent fiber sources, and supercontinuum fiber sources, is summarized and reviewed. Second, linearly polarized fiber lasers operating at other wavebands are reviewed, including the Er-doped fiber laser at--1.5 mu m, Tm-doped fiber laser at--2 mu m, Yb-doped fiber laser at the long waveband (1.1-1.2 mu m), Nd-doped fiber laser at--0.9 mu m, Raman fiber laser at 1.1 -1.2 mu m, and fiber lasers with manipulated output wavelength (central wavelength tunability, multiwavelength operation, and sweeping wavelength). Third, the research progress in pulsed linearly polarized fiber lasers with pulse durations ranging from nanosecond, picosecond to femtosecond is introduced. Then, the polarization dependence of nonlinear effects and mode instability is summarized, and mitigation methods of these two effects are briefly introduced. Finally, based on the aforementioned progress, some emerging techniques for further power scaling of linearly polarized fiber lasers are discussed, including, but not limited to, employment of low-quantum-defect fiber lasers schemes, exploitation of new laser materials such as single-crystal fibers, and adaptation of the coherent beam combination method. Conclusions and Prospects Linearly polarized fiber lasers have made rapid progress in multiple types of linewidths, multiwaveband operation, and pulsed laser outputs with different durations, thus opening up the potential to not only further improve the performance in laser processing, coherent detection, and other fields, but also enable new application fields in the generation of mid-infrared lasers, visible/ultraviolet light, and structured light generation. However, compared with their randomly polarized fiber laser counterparts, linearly polarized fiber lasers still present a large gap in spectral coverage range and output power. Therefore, one of the future directions for linearly polarized fiber laser research is the development of high-performance polarization-maintaining fibers and high-quality multi-waveband fiber devices. Another potential focus is the continuous improvement in the output power and performance of the laser, including the employment of low-quantum defect schemes, new gain media, and coherent beam combination technology, to meet the application requirements. Lastly, new laser bands can be explored to broaden the spectral range of linearly polarized lasers, such as the direct generation of linearly polarized visible lasers in an oscillator scheme and the generation of a wider range of tunable linearly polarized lasers based on nonlinear effects, to meet diversified application requirements. A series of scientific and engineering problems must be addressed, including the comprehensive suppression of mode instability and nonlinear effects, polarization state evolution, control and compensation, and broad-spectrum polarizability measurements. Addressing the relevant physical and technical problems will not only promote the performance of linearly polarized fiber lasers to a new level but also has great significance for the development of laser science and is expected to be promoted to other new applications.

This study presents a comprehensive investigation of high-power dichroic mirror spectral beam combination (DM-SBC) system with active tilt control through theoretical analysis and experimental validation. First, we establish an active-tilt-control simulation utilizing the stochastic parallel gradient descent (SPGD) algorithm, systematically examining the influence of key algorithm parameters including the gain coefficient gamma and iteration frequency f on the combining performance. Experimental implementation successfully demonstrates DM-SBC integration of three custom-developed kW-level fiber lasers with central wavelengths at 1050 nm, 1070 nm, and 1085 nm, achieving a maximum combined output power of 12 kW. The activation of active tilt control yields significant beam quality improvements, reducing average M2 values from 2.8/1.7 (x/y directions) to 1.8/1.6, while enhancing the metric function J by approximately two orders of magnitude. Both numerical simulations and experimental measurements consistently demonstrate the effectiveness of the proposed active control scheme in optimizing DM-SBC performance, particularly in beam quality enhancement and system stability improvement.

High-power fiber laser oscillators have been widely used in industrial processing, material processing, biomedical and other fields due to their compact structure, simple logic and strong power scalability. With the continuous improvement of performance requirements for lasers in industrial applications, bidirectional output fiber laser based on a single resonator structure have a broad application prospect. This paper first establishes a theoretical model for a 1050 nm bidirectional output fiber laser oscillator based on the steady-state rate equation, and simulates the relationship between the length of the gain fiber and output power, efficiency, and the intensity of stimulated Raman scattering (SRS). A high-power bidirectional output fiber laser with a central wavelength of 1050 nm is built using an ytterbium-doped fiber with a core/cladding diameter of 20/400 mu m. The output characteristics of the 1050 nm bidirectional output fiber laser oscillator under different pump methods (unidirectional pump, bidirectional pump) are experimentally studied in detail. With a total pump power of 5262 W, A-end output power of 1419 W and B-end output power of 3051 W were achieved, with a total output power of 4470 W, and the optical-to-optical conversion efficiency reached 84.9%. The corresponding beam qualities (M-2 factor) of both ends were 1.27 and 1.31 when the output powers reached 1458 W and 2733 W, respectively. By further optimizing the length of the gain fiber, the amplified spontaneous emission (ASE) and SRS were effectively suppressed. With a total pump power of 5262 W, the Raman suppression ratios at A-end and B-end were increased by about similar to 6.6 dB and similar to 8.1 dB, respectively. It is expected that higher output power can be achieved by increasing the pump power and optimizing the laser structure in the future.

We proposed and demonstrated a high-power bidirectional output all-fiber laser oscillator emitting at 1050 nm wavelength employing a novel composite cavity architecture. The laser incorporates two 10%-reflectivity output-coupler fiber Bragg gratings (FBGs) at both ends, and an additional FBG of 50%-reflectivity inserted within the resonant cavity. Compared to traditional bidirectional output fiber lasers with single resonant cavity, this composite cavity laser can significantly enhance the threshold of transverse mode instability (TMI), exhibiting similar to 19% and similar to 36% improvement in A-end pump and B-end pump schemes, respectively. Moreover, under bidirectional pump scheme, a total output power of 5.5 kW with no signs of TMI is achieved for the first time. The optical-to-optical conversion efficiency is 85.7% at the full output power, and the beam quality (M-2 factor) at respective outputs is 1.52 and 1.34. This work provides significant guidance for developing TMI-free high-power bidirectional output fiber lasers.

Coherent beam combining (CBC) of laser arrays is increasingly attracting attention for generating free-space structured light, unlocking greater potential in aspects such as power scaling, editing flexibility and high-quality light field creation. However, achieving stable phase locking in a CBC system with massive laser channels still remains a great challenge, especially in the presence of heavy phase noise. Here, we propose an efficient phase-locking method for a laser array with more than 1000 channels by leveraging a deep convolutional neural network for the first time. The key insight is that, by elegantly designing the generation strategy of training samples, the learning burden can be dramatically relieved from the structured data, which enables accurate prediction of the phase distribution. We demonstrate our method in a simulated tiled aperture CBC system with dynamic phase noise and extend it to simultaneously generate orbital angular momentum (OAM) beams with a substantial number of OAM modes.

Transverse mode instability (TMI) significantly limits the power scaling of ytterbium-doped fiber lasers. In this Letter, what we believe to be a novel TMI mitigation strategy is proposed and demonstrated in a bidirectional output fiber laser. On the basis of the continuous wave (CW) pump, integrating a quasi-continuous wave (QCW) pump can effectively improve the TMI threshold of the system. In the experiment, a QCW pump with a repetition rate of 1 kHz and a duty cycle of 10% was injected into a CW-pumped fiber laser oscillator, which successfully broke the power limit and alleviated the beam quality degradation. Moreover, when applying a pump modulation depth of approximately 68%, the TMI threshold was notably increased from 624 W in the free-running condition to 1093 W at end B, which is a 469 W (75%) improvement. At this time, the beam quality factor M2 at end B is approximately 1.48, and the stimulated Raman scattering suppression ratio is about 28 dB. Compared to conventional TMI mitigation methods, this approach provides active control in the time domain of fiber lasers, without compromising the optical structures, thereby effectively mitigating TMI and offering broad application prospects. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

Guar gum based bacterial cellulose (GG-BC) was generated from the soy sauce residue hydrolysate by in-situ fermentation, and its structure and performance were learned systematically. The GG concentration of 0.2 % was most suitable for GG-BC production with the yield of 1.21 g/L. During the in-situ fermentation, GG was implanted into the nano network of BC and thus altered its microstructure and properties. According to the FT-IR and NMR results, GG-BC had similar functional group structure and cellulose structural framework to those of BC. The degree of polymerization (DP) of GG-BC was 526.32-832.16, which was higher than that (426.32) of BC. Also, the GG-BC with low GG addition (0.2 % and 0.4 %) had a higher crystallinity than BC. Moreover, the GG-BC had a better heat tolerance than BC based on its higher temperature reaching the maximum degradation rate. The GG-BC with suitable GG addition had better texture characteristics, UV barrier property, swelling rate, and antioxidant activity than those of BC, showing that the in-situ fermentation with GG addition could promote the performance of GG-BC. Overall, this study can provide an attractive technology for both solving the environmental issue brought by soy sauce residue and producing high value-added GG-BC with good performance efficiently.

We present a comprehensive investigation on the laser properties of longitudinal spindle-shaped Yb-doped fibers (SYDFs), focusing on transverse mode instability (TMI) and stimulated Raman scattering (SRS), by conducting theoretical and experimental comparisons with traditional uniform double-clad fibers. The underlying physical mechanisms for TMI and SRS characteristics in SYDF amplifiers are revealed through detailed theoretical analysis. The experimental comparisons indicate that the SYDF showcases a slightly weaker TMI threshold than that of the uniform fiber with the same core-to-cladding ratio, showing ∼4.6% and ∼6.1% lower in the co-pump and counter-pump schemes, respectively. But the SRS suppression ratio of the SYDF amplifier was ∼7.6 dB higher than that of the uniform fiber at the same power level of 3.5 kW. When the output power of these two fiber amplifiers scaled to 6 kW, the SYDF still exhibited a stronger laser performance as compared to traditional uniform fiber. To the best of our knowledge, this is the first comprehensive comparison between SYDFs and uniform fibers in both experimental and theoretical regimes. This work provides significant reference for the design and development of what we believe to be new silica-based fibers to alleviate TMI and SRS in high-power fiber lasers.