基于空芯反谐振光纤的高功率激光传输技术研究进展(特邀)

Research Progress of High⁃Power Laser Transmission Technology Based on Hollow⁃Core Anti⁃Resonant Fibers(Invited)

高功率光纤激光器凭借其转换效率高、性能稳定、光束质量好以及结构紧凑等优点在诸多领域被广泛应用。随着输出功率的不断提升,输出光谱范围不断拓宽,传统石英光纤由于材料损伤、非线性以及材料本征吸收等因素无法满足高功率激光柔性传输的需求。近年来,空芯反谐振光纤的快速发展吸引了高功率激光传输领域科研人员的广泛关注。该光纤通过反谐振反射光波导效应将光限制在纤芯空气介质中传输,极大地降低了模场与石英材料的重叠度,具有高损伤阈值、低非线性等优良性能,在激光传输领域取得了一系列突破性进展。在传输功率方面,目前国际上基于空芯反谐振光纤已经实现了1 kW连续激光1 km传输、30 mJ单脉冲能量纳秒激光传输以及20 GW峰值功率超短脉冲激光传输,展现了其在功率提升方面的潜力。在传输波段方面,空芯反谐振光纤通过调节石英壁厚对传输通带进行调控,已经实现了从紫外波段到中红外波段激光传输。北京工业大学先进激光及光纤技术研究团队基于高性能空芯反谐振光纤的设计及制备技术,在国内率先开展了基于空芯反谐振光纤的高功率激光传输研究,已经实现了3 kW连续激光百米传输和26.8 MW皮秒脉冲激光柔性传输,传输波段从紫外355 nm拓展至中红外4.35μm,其中在3.1μm波段传输的平均功率突破了20 W,处于世界领先水平。本文简要介绍了空芯反谐振光纤的发展历程,并对基于该光纤的高功率激光传输关键技术及研究进展进行了相关讨论。

Significance The performance of high-power fiber lasers has rapidly improved over the years.Consequently,high-power fiber lasers have become instrumental in the development of industrial processes and national defense technologies.Researchers are attempting to further improve the output power of high-power fiber lasers,but inefficient transmission methods are limiting their widespread application.Free-space transmission introduces complex spatial optical paths,resulting in insufficient flexibility and stability.Therefore,the demand for high-power laser transmission based on flexible fibers is increasing.Traditional solid silica fibers are available for such applications.However the damage threshold and material nonlinearity eventually affect them and thereby limit the increases of transmission power and length.Moreover,the severe material absorption in the mid-infrared band and the large Rayleigh scattering loss at short wavelengths of silica materials limit the laser transmission range.Hollow-core anti-resonant fibers(HC-ARFs)provide novel solutions for flexible high-power laser transmission by guiding light through air,a vacuum,or a gas-filled hollow core.Compared with solid-core fibers,HC-ARFs inherently reduce the overlap between the optical field and glass structure by five orders of magnitude,which results in low optical nonlinearity and a higher damage threshold.Recently,numerous multilayer structures have emerged,based on the knowledge of light-guiding mechanisms,which rapidly decrease the losses of HC-ARFs.The unique properties of these innovatively structured HC-ARFs offer significant potential in terms of transmission distance,flexibility,and power-handling capacity.In terms of their transmission bands,HC-ARFs regulate the operational window by adjusting the silica wall thickness.HC-ARFs overcome the transmission bandwidth of silica materials and realize laser transmission from the UV band to the mid-infrared band.Progress The rapid development of HC-ARFs has attracted extensive attention from researchers in the field of high-power laser transmission,and a series of breakthroughs have been achieved.Owing to the high damage threshold and low nonlinearity of HCARFs,most research teams focus on the enhancement of transmission power.Currently,in terms of continuous-wave laser transmission,3 kW high-power laser transmission over 110 m and 1 kW high-power laser transmission over 1 km have been achieved using HC-ARFs.In terms of nanosecond high-energy laser transmission,30 mJ single pulse energy transmission has been achieved using HC-ARFs.In terms of ultra-short pulse laser transmission with peak power,20 GW of peak power transmission has been achieved using HC-ARFs.The above achievements fully demonstrate the enormous potential of HC-ARFs in the field of high-power laser transmission.The implementation of high-power laser transmission in special wavelength bands based on HC-ARFs is also an important direction for development.In the mid-infrared band,HC-ARFs have good physicochemical properties and low absorption losses.Currently,an HC-ARF can achieve up to 6μm wavelength guidance.In terms of high-power laser transmission,our team has exceeded 20 W average power in the 3.1μm band using HC-ARFs.In the ultraviolet bands,HC-ARFs overcome the limit of Rayleigh scattering loss to achieve low loss transmission.Our team realized high power ultrashort pulse laser transmission in the UV band using HC-ARFs,achieving a peak power of 5.3 MW.Conclusions and Prospects HC-ARFs have the characteristics of low nonlinearity,low dispersion,a high damage threshold,and a controllable number of transmission modes.High-power laser transmission based on HC-ARFs has become a research hotspot.With the improvement of the structural design and fabrication processes for HC-ARFs,the transmission losses of multiple important laser bands are significantly reduced.Research reports on high-power laser transmission based on HC-ARFs continue to emerge,and high-power continuous laser and pulse laser transmission from the ultraviolet to mid-infrared bands has been achieved.However,there is still significant space for improvement,such as further improving transmission power and efficiency and exploring full fiber integrated transmission methods under high power,among others.With the in-depth research and resolution of related technical difficulties,high-power laser transmission technology based on HC-ARFs will become a new generation of transmission solutions and thereby promote the rapid development of related application fields.