1μm波段低量子亏损光纤激光研究进展(特邀)

Research progress of low-quantum-defect fiber laser at 1μm band(invited)

量子亏损对高功率光纤激光器内的废热产生和光光转换效率具有重要影响,光纤激光器输出功率的提升过程可以视为不断与量子亏损作斗争的过程。文中梳理了近年来1μm波段低量子亏损光纤激光的重要进展,重点介绍了稀土掺杂增益和拉曼增益两种体制的光纤激光器在实现低量子亏损输出方面的相关工作。在稀土掺杂光纤激光器中,采用级联泵浦、多组分掺杂、强泵浦等技术可降低激光器的量子亏损,其中量子亏损≤1%的掺镱光纤激光器已实现400 mW功率输出。在拉曼光纤激光器中,通过采用特殊掺杂、泵浦光谱调控、增益竞争抑制等技术,量子亏损≤1%的拉曼光纤激光器已实现百瓦级功率输出,并成功验证包层泵浦方案的可行性,表明其在实现高功率低量子亏损输出方面具有重要潜力。

Significance Power scalability of fiber lasers have attracted a great deal of attention for its remarkable features,such as excellent beam quality,high conversion efficiency,flexible operation,and wide applications in biomedicine,intelligent manufacturing,energy exploration,defense and security.However,there have been no reports of significant operation power breakthroughs of near-single-mode fiber laser since the first demonstration of 10 kW-level system in 2009.The wasted heat accumulation,which can induce thermal lens and transverse mode instability effects,is one of the most important limitation factors.Quantum defect,defined as(1-λp/λs),whereλp is the pump wavelength andλs is the lasing wavelength,has always been a key parameter in high-power fiber lasers.High quantum defect not only limits the conversion efficiency but also increases the thermal load in fiber lasers.In hence,much research on low quantum defect fiber laser has been reported in the past decades.Progress This paper first introduces the performance exploration of high-power fiber laser at 1μm band,including the power scaling and corresponding quantum defect decrease.It can be said that the power scaling progress of fiber lasers is also a continuous struggle against waste heat and other factors.As to low quantum defect fiber laser,the reported works mainly focus on two different technical schemes based on rare earth doped fiber and passive fiber.For the convenience of description,this article stipulates that the quantum defect of low quantum defect fiber lasers is≤4.50%,and the quantum defect of ultra-low quantum defect fiber lasers is≤1%.Then,ytterbium-doped fiber lasers with low quantum defect are summarized.In 2011,Wirth et al.demonstrated a 2.9 kW fiber laser operating at 1071 nm that is tandem-pumped by a 1030 nm thin-disk laser,and the corresponding quantum defect is about 3.83%(Fig.1).In 2014,Chang et al.presented a fiber laser with a maximal output power of 5.7 W and a quantum defect of 1.9%(Fig.2).To further reduce the quantum defect of fiber lasers,some specially designed active fibers and high pumping intensity methods are adopted.For example,in 2018,Yu et al.demonstrated a 400 mW-level fiber lasers with less than 1%quantum defect via ytterbiumdoped multicomponent fluorosilicate fibers(Fig.5).Additionally,Raman fiber lasers with low quantum defect are reviewed.Based on common silicon fiber,a maximal power of 3 kW-level with a quantum defect of 4.42%(Fig.7)and a maximal power of 6.2 W with a quantum defect of 0.56%were achieved.To further improve the operation power of ultra-low quantum defect fiber laser,the scheme enabled by boson peak in phosphosilicate fiber was presented and realized by Zhang et al.in 2020(Fig.14).In 2021,Ma et al.demonstrated a 100 W-level ultra-low quantum defect fiber laser with a quantum defect of 0.97%.What's more,cladding pump scheme was also been validated(Fig.15).Conclusions and Prospects The important progress of low quantum defect fiber laser operating at 1μm band is reviewed.And the manuscript mainly focuses on two different technical schemes based on rare earth doped fiber and passive fiber.In rare earth doped fiber based lasers,the utilization of tandem-pumping,multi-component doping and strong pumping schemes can reduce the quantum defect,and the related ytterbium-doped fiber lasers with quantum defect≤1%have achieved 400 mW-level output power.In Raman fiber lasers,the maximal output power of 100 W-level with a quantum defect of≤1%has been demonstrated with the aid of techniques such as special doping,pump spectrum regulation,and gain competition suppression.The feasibility of cladding pumping scheme has also been verified successfully,indicating its significant potential in achieving high-power and low quantum loss output.