Developing narrow-linewidth and stable 2.0 mu m high-power laser sources is essential for mid-infrared applications. Here, we report the self-pulse dynamics and pulse suppression strategies in Tm-doped fiber within a multi-longitudinal-mode composite cavity seed source. The evolution of self-pulses in Tm-doped fiber under different configurations was experimentally investigated. The results demonstrate that the composite cavity significantly suppresses self-locked mode pulses on shorter time scales, improving time-domain stability by up 75% compared to a single cavity. Furthermore, based on the optimization of the composite cavity seed laser and system integration, a narrow-linewidth laser output has been achieved in the backward pumping MOPA amplifier structure. The maximum unsaturated output power reaches 432.1 W, with a slope efficiency of 58.9%, 3 dB spectral linewidth of 0.0833 nm, and a beam quality factor M-2 value of similar to 1.60. Notably, the limitation of TMI and SBS effects was not observed at high power output levels. The amplification structure based on a multi-longitudinal-mode composite cavity paves the way for developing compact, high-power, narrow-linewidth Tm-doped fiber lasers for practical applications.

Improving the nonlinear effect thresholds and performance of fiber laser systems becomes essential for developing high-power narrow-linewidth fiber lasers. We have designed and fabricated the novel LMA-30/400 Ybdoped fiber with an ultra-low cladding absorption of 0.22 dB/m@915 nm and a core NA of 0.065. Investigating the influence of bending diameter on cladding absorption indicates that enlarging the bending diameter can effectively reduce cladding absorption. A narrow-linewidth laser with a maximum output power of 5020 W has been achieved based on white-noise phase modulation under non-stabilized 976 nm LD pumping, where the spectral linewidth Delta(lambda 3dB) of 0.135 nm, the slope efficiency of 81.4 % and the beam quality of M-2 of similar to 1.21. Importantly, no Transverse Mode Instability (TMI) was observed even at the 5-kW level. This work provides valuable insights for the future development of ultra narrow-linewidth lasers with high power and high beam quality.

热效应是影响高功率光纤激光系统安全运行的重要因素之一.探索光纤激光系统热效应产生的源头,积极开展热效应控制技术研究,采取合理措施抑制热集中现象,大幅提高光纤激光系统的模式不稳定阈值以避免模式劣化现象,对于进一步提升光纤激光系统安全稳定输出功率具有非常重要的现实意义.以广泛使用的端面集中泵浦技术为例,概述了高功率连续光纤激光系统的主要热效应来源,提出了针对不同热效应需要采取的解决方案与合理化建议.最后着重介绍了长距离分布式侧面泵浦技术和泵浦增益一体化复合功能激光光纤,展望了万瓦级超高功率光纤激光器的未来发展前景.

万瓦级YDF掺镱双包层有源激光光纤是高功率光纤激光器的核心增益介质,是制约我国光纤激光技术进步的瓶颈短板,万瓦级以上超高功率激光光纤的理论设计与制备工艺等关键技术亟需突破.

相较于普通有源激光光纤( YDF) ,保偏型有源激光光纤( PM-YDF)需要设计低数值孔径纤芯结构,构建合适的双折射系数,制备芯包比合适的稀土掺杂光纤预制棒,制备超大尺寸的硼棒,拉制熊猫保偏光纤等诸多环节,真正体现着"细节决定成败"的工业规范要求.保偏型有源激光光纤是激光光纤材料分类中技术含量相对较高的产品,因其制作难度大,工艺流程复杂,国内尚无相关产品得以报道.

LMA-14/250-YDF有源激光光纤逐渐取代了LMA-20/400-YDF有源激光光纤,其具有巨大的成本优势和良好的稳定性,已成为工业光纤激光产业中主流的千瓦级光纤激光材料,产品竞争力强,市场容量大。LMA-14/250-YDF光纤需满足Yb掺杂浓度高（915nm处的吸收系数为0.7～0.9dB/m）、纤芯背景损耗低（1200nm处的损耗系数≤15dB/km）、斜率效率高（谐振腔结构的斜率效率≥70%）和抗光子暗化（功率波动≤3%）等严格的产业化先决条件。因此,LMA-14/250-YDF光纤的制备工艺难度大,技术含量很高,我国目前广泛使用的LMA-14/250-YDF有源激光光纤还是以进口产品为主,相关的国产光纤鲜有报道。

Yb-doped F-rich aluminophosphosilicate LMA-25/400-YDF laser fiber was fabricated by chelate precursor doping technique. 3.03 kW@1080nm laser output was achieved in an oscillator configuration with an optical-to-optical efficiency of 71.5% and shown excellent stability.

We fabricated and reported a pedestal fiber with Yb/Ce-codoped aluminosilicate (Al2O3-SiO2) core and germanosilicate (GeO2-SiO2) pedestal. This newly-optimized chelate precursor doping technique enables us to make homogeneous large-core pedestal fiber with strong pump absorption from Yb3+ ions about 3.66dB/m at 915nm. The fiber core was homogeneously doped with 4450ppm Yb3+, 11600ppm Al3+ and 1800ppm Ce3+, and surrounded by pedestal layers with 25000ppm Ge4+. The results indicate all-gas-phase chelate precursor doping technique is highly competitive for the fabrication of pedestal fiber towards narrow-linewidth fiber laser.

A single-mode bismuth-doped tellurite glass fiber using a multi-stage fiber fabrication method was fabricated. It features low propagation loss of 0.86 dB/m and high effective nonlinear parameter γ of 417 W–1•km–1 at 1550 nm.

A series of 75TeO(2)-(20-x)ZnO-5Na(2)O-xBi(2)O(3) (mol%) glasses with x = 0, 6, 8, and 10 (TZN-Bi) were fabricated via the special melt-quench technique and characterized as candidates for fiber laser glasses. Optical absorption studies revealed that increasing the Bi2O3 content increased the cutoff wavelength and Urbach energy (Delta E) and decreased the optical band gap energy (E-opt): these trends were attributed to the structural changes occurring in these glasses. In addition to optimizing the linear transmittance and absorption, Bi2O3 increased the nonlinear refractive indexes and the Raman gain coefficients. The TZN-Bi glasses exhibited large third-order optical nonlinearities with a maximum n(2) of 2.85 x 10(-15) cm(2)/W. The peak Raman gain coefficients (29 x 10(-11) cm/W) were approximately 30 times that of SiO2. These results indicate that the Bi2O3-modified glasses are promising candidates in optical applications such as Q-switching elements and Raman gain amplifiers. (C) 2019 Elsevier B.V. All rights reserved.

We fully demonstrated an ytterbium (Yb) doped triple-clad laser fiber with intense pump absorption, high efficiency, and laser stability. P5+/Al3+ molar ratio in the central region of fiber core was specially designed to be ~1.08 for compensating P2O5 evaporation, while the ratio in the outer region was set as ~0.92 for obtaining a flattened refractive index profile. Applying a two-stage deposition process, one-time collapse technique, low-temperature multi-times sintering, and suitable flow of pure POCl3 during sintering and collapsing process were instrumental in decreasing and offsetting element evaporation. Measured in an all-fiber master oscillator power amplifier configuration, the 7-m-long fiber obtained 1.39 kW near-single-mode laser output at 1079.6 nm with a slope efficiency of 85.2% and a beam quality M2 of 1.36. Output laser spectrum with no sign of nonlinear-related peaks and a narrow 3-dB-bandwidth of ~0.33 nm was obtained. The fiber-based laser setup was kept at the maximum power for 1 h with power degradation less than 0.21%. The results demonstrated Yb-doped aluminophosphosilicate triple-clad fiber is a highly competitive candidate for commercial high-power laser and high-power narrow-linewidth fiber laser.

Based on a master oscillator power amplifier configuration, laser performance of commercial Nufern-20/400-8M Ybdoped aluminophosphosilicate ternary laser fiber was investigated. Pumped by 976 nm laser diodes, 982 W laser output power was obtained with a slope efficiency of 84.9%. Spectrum of output was centered at 1066.56nm with 3dB bandwidth less than 0.32 nm, and the nonlinearity suppression ratio was more than 39dB. Beam quality of Mx2 and M2y were 1.55 and 1.75 at 982 W, respectively. The laser performance indicated that Nufern-20/400-8M Yb-doped aluminophosphosilicate ternary laser fiber is highly competitive for industry fiber laser use.

We fabricated a (8+1)-type pump-gain integrated functional laser fiber with 8 passive pump-fibers and 1 signal-gain fiber. 8.74 kW laser output with optical-to-optical efficiency of 81% was achieved in counter-pump MOPA setup.

By using the MCVD system and the all-gas-phase chelate precursor doping technique, we fabricated an Yb-doped aluminophosphosilicate fiber with 20 mu m-core and 400 mu m-clad in diameter, i.e., 20/400 Yb-APS fiber. The fiber core was doped with 1100 ppm Yb3+, 7200 ppm Al3+, and 8000 ppm P5+. With a molar ratio of Al/P close to 1:1, low refractive index difference and suitable numerical aperture was obtained for large-mode-area fiber design. Directly forward pumped by 976 nm laser diodes, 11-m-long 20/400 Yb-APS fiber presented 3.03 kW laser output at 1080 nm with a slope efficiency of 76.6% and beam quality M-2 of similar to 1.58. Up to this power level, no signs of instable beam profile, beam quality worsening, and laser power roll-over were obtained, indirectly justified no obvious mode instability in the whole laser setup. To directly characterize its power stability and photodarkening effect, the fiber laser was kept at similar to 2.1 kW for over 500 min with power degradation less than 1.1%. These results indicated that the all-gas-phase chelate precursor doping technique is highly competitive for Yb-APS fiber fabrication toward high-power laser, and the fabricated fiber is very suitable for 2 kW-level or above commercial fiber laser development.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text C. Gao, C. Li, Y. Wang, H. Zhan, K. Peng, L. Zhang, L. Ni, X. Wang, L. Jiang, S. Liu, Y. Li, J. Wang, F. Jing, and A. Lin, "5kW 30/600Yb-doped Aluminophosphosilicate Laser Fiber," in Conference on Lasers and Electro-Optics, OSA Technical Digest (online) (Optica Publishing Group, 2018), paper SF3I.1. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

We fabricated an ytterbium-doped phosphorus-low aluminophosphosilicate ternary laser fiber. Owing to photodarkening and mode instability, the fiber-based kW-level laser setup showed obvious degradation of laser power and slope efficiency as compared to that with cladding-power-stripper-free.

We fabricated an Yb-doped triple-clad fiber consisting in adding to aluminophosphosilicate core and F300-pump cladding, low-refractive-index fluorine doped silica cladding, and demonstrated its laser performance based on an all-fiber oscillator. MCVD system, all-gas-phase chelate precursor doping technique, and a simple over-cladding process were applied to make Yb-doped aluminophosphosilicate triple-clad fiber preform. Ultra-thin substrate tube and a two-stage deposition process were proposed to decrease and offset elements evaporation. The outer region of fiber core was tested with similar to 1050 ppm Yb2O3, similar to 10,800 ppm Al2O3 , and similar to 9950 ppm P2O5 , while the central region was doped with similar to 600 ppm Yb2O3 , 8100 ppm Al2O3 , and similar to 7000 ppm P2O5 , respectively (ppm is in molar here). Two-stage deposition process and triple-clad design results in pump absorption from Yb3+ ions about 0.67 dB/m at 915 nm. Tested in an all-fiber oscillator configuration forward-pumped by 915 nm laser diodes, 28 m-long triple-clad fiber presented 560 W laser output with optical-to-optical efficiency of 68.7%, and the corresponding beam quality M-2 is similar to 1.18. The results indicate all-gas-phase chelate precursor doping technique in combination with overcladding technique is potential to manufacture high power triple-clad fiber, and ultra-thin substrate tube as well as two-stage deposition process are very effective ways to decrease and offset element evaporation.

By a chelate precursor doping technique, we designed and fabricated an ytterbium/cerium codoped aluminosilicate fiber for noticeable suppression of photodarkening and demonstrated its laser performance. Cerium/ytterbium ions ratio of 0.5 was specially designed to mitigate photodarkening. Aluminum/fluorine ions ratio of 1 was devised to keep low numerical aperture of fiber core. The measurements showed the fiber core was homogeneously doped with ∼0.12 mol% Yb2O3, ∼0.05 mol% Ce2O3, ∼0.5 mol% Al2O3, and ∼0.2 mol% SiF4, respectively. Tested in a master oscillator power amplifier system, the fiber presented 1930 W laser output power with optical-to-optical efficiency of 79.2%. Stabilized at 1850 W for over 500 min, the output power presented a relatively small power degradation of <1.04%, directly justifying a strong photodarkening resistance. These results demonstrated that ytterbium/cerium codoped aluminosilicate fiber with appropriate concentration ratios of dopants could be an ideal choice for 2 kW-level commercial high power laser applications.

To incorporate sufficient pumping power, a large-scale Yb-doped aluminophosphosilicate (Al2O3 -P2O5-SiO2, APS) fiber with 30-μm core and 900-μ m inner clad in diameter, i.e., a 30/900 Yb-APS fiber, was theoretically designed and experimentally fabricated by using modified chemical vapor deposition system combining with chelate precursor doping technique. Analyzed by an electron probe microanalyzer, the dopant concentration of Yb2O3, Al2O 3, and P2O5 was estimated to be 0.14 mol%, 1.1 mol%, and 1.4 mol%, respectively. Based on an all-fiberized master oscillator power-amplifier laser setup directly forward pumped by commercial 976-nm laser diodes, 6.85-kW laser output at 1079.79 nm was achieved with an optical-to-optical efficiency of 67.1%, and the beam factor of $M^{2}$ was 2.38. The results indicate that large-scale Yb-APS fiber is quite competitive for high-power fiber laser development.