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2004年,丹麦技术大学AGGER等人首次抽运掺铥光纤得到1735 nm单频激光输出[22]。近10年来,1.7 μm波段激光器在性能及应用方面得到了突飞猛进的发展,逐渐成为国际研究热点。除光纤激光器外,1.7 μm波段非光纤激光器[23-25]、1.7 μm波段放大器[26-30]及宽带光源[31-32]同样取得了一定成果。
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目前,抽运掺铥离子光纤是实现1.7 μm波段激光最常见的手段,但掺铥光纤在1.65 μm~1.8 μm短波工作表现出强烈的三能级行为[33],需要高粒子数反转才能达到激光阈值,且需要一种合适的波长选择技术来抑制发射峰处的激光[34-36]。近5年来,该波段激光器在效率和输出上均得到了一定程度的提升。2018年,PARK等人采用1565 nm连续激光器抽运1.3 m长的铥钬共掺光纤且通过布喇格光纤光栅进行滤波,实现了平均功率达到百毫瓦、且斜率效率为23%、中心波长1706.3 nm的连续激光输出[37]。2019年,BURNS等人通过对掺铥光纤进行纤芯抽运得到斜率效率高达80%,证明了掺铥光纤激光器在1726 nm下的高功率短波长工作[38]。实验结构和结果如图 1所示。
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2015年,俄罗斯科学院用掺铋的高锗光纤研制了波长为1.7 μm的连续波区的瓦级全光纤激光器[39],且报道了掺铋光纤和光纤激光器在1600 nm~1800 nm光谱范围内发展的最新结果[40]。2018年,FIRSTOV等人总结了光谱范围在1600 nm~1800 nm的掺铋光纤激光器[41]。2019年,麦吉尔大学NEMOVA等人对工作在1.7 μm波长范围内的双波长级联腔掺铋光纤激光器进行了全面的理论研究,通过级联两个反射率不高的光纤布喇格光栅(其中一个峰值反射率为95%的,以1.725 μm为中心;第2个峰值反射率为90%,以1.729 μm为中心)实现了双波长连续激光输出[42]。实验结构和结果如图 2所示。
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非线性效应也是产生1.7 μm波段光输出的有效手段,通过基于受激喇曼散射及孤子自频移等方法可突破抽运掺杂稀土光纤受到波长限制这一问题,获得任意波长的激光输出。2019年,THOUROUDE等人通过抽运单模光纤,实现了在1650 nm~1680 nm的光谱范围喇曼光纤激光器(Raman fiber laser,RFL)光源,最大输出功率可达6.25 W[43]。同年,THOUROUDE等人展示了一种在1540 nm处抽运掺铒光纤的1阶随机喇曼光纤激光器[44],在1650 nm处的最高输出功率为9.2 W,转换效率为74%。实验结果如图 3所示。
表 1为国外1.7 μm波段连续光纤激光器研究进展。
表 1 国外1.7 μm波段连续光纤激光器研究进展
Table 1. Research progress in foreign 1.7 μm band continuous fiber laser
技术手段 抽运波长/nm 输出波长/nm 输出功率/mW 效率/% 激光腔型 年份 国家 参考文献 THDF 1565 1706.3 249 23 线性腔 2018 韩国 [37] TDF 1580 1726 47000 80 线性腔 2019 英国 [38] BDF 915 1705 1050 33 线性腔 2018 俄罗斯 [41] BDF 1550 1725,1729 0.6,1.1 — 线性腔 2019 加拿大 [42] 非线性效应 1532~1560 1655,1679 6250,5000 — — 2019 法国 [43] 非线性效应 1540 1650 9250 — — 2019 法国 [44] -
1.7 μm波段脉冲光纤激光器随着1.7 μm波段连续光纤激光器的不断成熟,同样得到了快速发展,取得一定成果。光纤激光器产生超短脉冲的机理有两种:Q开关[45-46]和锁模[47-49]。Q开关技术产生的脉宽通常为纳秒级,而锁模技术产生的脉宽可达到飞秒级。早在2013年,美国亚利桑那大学NGUYEN等人通过抽运大模场晶体光纤实现了可调谐范围为1600 nm ~1780 nm、脉冲宽度为100 fs的1.7 μm波段脉冲激光器[50]。
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2016年,NORONEN等人研制了1705 nm~1805 nm的可调谐谐波锁模激光器[51],该光源利用铥钬共掺光纤作为增益元件,利用频移反馈和非线性偏转技术(nonlinear polarization rotation,NPR),在1735 nm处获得宽度为630 fs的最短脉冲。2017年,汉堡大学CHUNG等人基于NPR技术在31 MHz重复频率下运行自制5 W掺铒光纤激光器[52],获得了可在1.3 μm~1.7 μm范围内连续调谐的飞秒脉冲,脉冲能量大于4.5 nJ。
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2018年,俄罗斯科学院KHEGAI等人设计了1.7 μm波段带有非线性放大环镜(nonlinear amplifying loop mirror,NALM)的8型腔激光器[53],在重复频率为3.57 MHz下,产生宽度为17 ps、能量为84 pJ的脉冲。实验结构和结果如图 4所示。
2021年,新加坡南洋理工大学CHEN等人提出了一种W型掺铥光纤1.7 μm波段高能飞秒脉冲激光器[54],在1.7 μm~1.8 μm区域获得174 fs的稳定脉冲,脉冲能量最高为128 nJ。
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2019年,法国萨克雷大学通过抽运非线性光纤产生了从1700 nm~2050 nm连续可调谐飞秒脉冲,实现了脉冲宽度在150 fs以下,转换率大于50%、全光纤保偏可调谐脉冲激光器[55]。
2020年,GRIMES等人演示了工作在1.7 μm波段的级联喇曼光纤激光器[56],在1692 nm实现了功率高达104 W的连续激光输出,激光器产生的喇曼激光脉冲范围从11.5 mJ(脉冲宽度为100 μs)~10 J(脉冲宽度为100 ms),平均功率高达23 W。
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2020年,新加坡南洋理工大学CHEN等人利用半导体可饱和吸收镜(semiconductor saturable absorber mirror,SESAM)实现了中心波长为1755 nm的高能脉冲激光器[57],峰值功率输出为12.1 kW,测量脉冲宽度为2.76 ps,能量为32.7 nJ。实验结构和结果如图 5所示。
表 2为国外1.7 μm波段脉冲激光器研究进展。
表 2 国外1.7 μm波段脉冲激光器研究进展
Table 2. Research progress in foreign 1.7 μm band pulse laser
抽运波长/nm 重复频率/MHz 输出波长/nm 脉冲产生方式 脉冲能量 脉宽 年份 国家 参考文献 1556 232.6~554.6 1735 NPR 21 pJ 630 fs 2016 芬兰 [51] 1030 31 1300~1700 NPR 10.6 nJ 85 fs 2017 德国 [52] 1157 3.57 1700 NALM 84 pJ 17 ps 2018 俄罗斯 [53] 1570 7.82 1785 NALM 128 nJ 174 fs 2020 新加坡 [54] 976 40 1700~2050 非线性效应 1 nJ 150 fs 2019 法国 [55] 1117 — 1700 非线性效应 11.5 mJ~10 J 100 μs~100 ms 2020 丹麦 [56] 1565 5.5 1755 SESAM 32.7 nJ 2.76 ps 2021 新加坡 [57] -
2015年,国防科技大学XUE等人通过抽运铥钬共掺光纤实现可调谐波长范围为1727 nm~2030 nm的环形光纤激光器[58],由于腔内没有波长限制,其可调谐范围达到300 nm,是迄今为止报道的全光纤稀土掺杂激光器的最宽调谐范围。实验结构和结果如图 6所示。
2017年,中国科学院西安光学精密机械研究所设计了一种基于双向抽运和光纤布喇格光栅的线形腔连续激光器[59],其输出波长为1706.75 nm,功率为3.15 W。天津大学学者在1.7 μm波段激光器方面也做了一些研究:2020年,ZHANG J X等人搭建了1.7 μm波段全光纤激光器,采用1570 nm激光器抽运掺铥光纤,并通过波分复用器(wavelength division multiplexer,WDM)和单模-多模-单模等结构抑制掺铥光纤的长波增益,获得了1720 nm激光输出[60];ZHANG L等人建立了一种环形腔结构的全光纤激光器[61],利用布喇格光纤光栅进行滤波,在6 W发射抽运下,实现了中心波长为1720 nm、功率为2.36 W激光输出,实验结构和结果如图 7所示;2021年,ZHANG J X等人通过抽运掺铥光纤实现了首个有效1.7 μm波段单频光纤激光器[62],输出功率达到407 mW;同年,ZHANG L课题组证明了一种高效的高功率单频掺铥光纤环形激光器[63],工作波长为1720 nm,通过加入光纤布喇格光栅,实现了单纵模工作,在3.75 W发射抽运功率下,最大单频输出功率可达1.11 W,斜率效率为46.4%;该课题组还介绍了一种有效的1.7 μm掺铥光纤激光器[64],实现了双向抽运,并且开发了一个速率方程模型以优化光纤长度和输出耦合,实验在抽运功率为10 W的情况下,获得了中心波长为1720 nm、最大输出功率为1.13 W的激光输出。2021年,华南理工大学CEN等人对1.7 μm波段的短波长分布布喇格反射(distribution Bragg reflector,DBR)单频光纤激光器进行了实验研究[65],实现了工作波长为1727 nm、信噪比大于60 dB稳定的单纵模激光输出。
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2019年,国防科技大学ZHANG等人实现了一种1.7 μm波段可调谐随机喇曼光纤激光器[66],实验通过利用1550 nm的自发放大辐射(amplified spontaneous emi-ssion,ASE)光抽运喇曼光纤得到波长为1715 nm、输出功率为14.5 W,且光谱纯度达到98%的激光输出。实验结构和结果如图 8所示。
表 3为国内1.7 μm波段连续光纤激光器研究进展。
表 3 国内1.7 μm波段连续光纤激光器研究进展
Table 3. Research progress in domestic 1.7 μm band continuous fiber laser
技术手段 抽运波长/nm 输出波长/nm 输出功率/W 效率/% 激光腔型 机构 年份 参考文献 THDF 1550 1727~2030 0.408 42.6 环形腔 国防科技大学 2015 [58] TDF 1550 1706.75 3.15 42.1 线性腔 西安光机所 2017 [59] TDF 1570 1720 0.121 5.7 环形腔 天津大学 2020 [60] TDF 1570 1720 2.36 50.2 环形腔 天津大学 2020 [61] TDF 1570 1720 0.407 22.7 环形腔 天津大学 2020 [62] TDF 1570 1720 1.11 46.4 环形腔 天津大学 2020 [63] TDF 976 1720 1.13 13.5 线性腔 天津大学 2020 [64] TGF 1610 1727 0.0124 4.81 线性腔 华南理工大学 2021 [65] 非线性效应 1550 1715 14.5 — 线性腔 国防科技大学 2021 [66] -
2017年,上海交通大学FANG等人基于抽运色散位移光纤(dispersion shifted fiber,DSF)产生1.7 μm波段的超短脉冲[67],通过优化DSF长度,在1.70 μm~1.74 μm范围内实现了低于200 fs的脉冲,转换效率为76%,最大输出功率为26.8 mW,单脉冲能量可达0.7 nJ。2021年,国防科技大学PEI等人首次证明了一种具有全光纤结构的可调谐脉冲1.7 μm波段光纤喇曼激光器[68],通过抽运9 m充氢气(H2)的空心晶体光纤(hollow core photonic crystal fiber,HC-PCF)获得输出功率为1.63 W的1.7 μm波段激光发射。LI等人通过抽运9 m长的充H2的HC-PCF,得到中心波长为1705 nm、功率为3.3 W、调谐范围为1693 nm~1705 nm的输出,且仿真结果与实验结果相符,实现了重复频率为1.3 MHz、脉冲宽度约为15 ns、斜率效率为84%的脉冲光纤激光器[69],结构和实验结果如图 9所示。2021年,PEI等人通过优化实验结构实现了1.7 μm脉冲光纤气体喇曼激光振荡器[70],当重复频率为6 MHz、脉宽为30 ns时,在1693 nm处获得了1.5 W的最大喇曼功率。
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2021年,华南师范大学CHEN等人通过抽运3.3 m掺铥光纤,利用NPR技术实现中心波长位于1746 nm,10 dB光谱宽度约为17 nm、重复频率为17.84 MHz、输出功率为3.55 mW、脉冲宽度为3.9 ps的脉冲光纤激光器[71]。结构和实验结果如图 10所示。
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2018年,厦门大学DU等人演示了基于新型模间拍频调制(intermode-beating modulation,IM)技术,利用抽运THDF的1.7 μm波段光纤脉冲激光器[72],其中心波长为1781.5 nm,3 dB线宽为1.5 nm,当重复频率为145 kHz时,最小脉冲宽度为1.4 s,输出功率为3.4 mW。
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2020年,西北大学的HE实现了1.7 μm波段全保偏飞秒光纤激光输出[73],其平均功率为35 mW,中心波长为1.7 μm,脉冲宽度为368 fs,光光转换效率为66%。实验结构和结果如图 11所示。
表 4为国内1.7 μm波段脉冲光纤激光器的研究进展。
表 4 国内1.7 μm波段脉冲光纤激光器研究进展
Table 4. Research progress in 1.7 μm band pulse fiber laser in China
抽运波长/nm 重复频率/MHz 输出波长/nm 脉冲产生方式 脉宽 输出功率/mW 年份 机构 参考文献 1600 38.8 1700~1740 非线性效应 200 fs 26.8 2017 上海交通大学 [67] 1540~1550 1 1693~1705 非线性效应 10 ns 1630 2021 国防科技大学 [68] 1540~1550 1.3 1693~1705 非线性效应 13 ns 3300 2021 国防科技大学 [69] 1540 6 1693 非线性效应 30 ns 1500 2021 国防科技大学 [70] 1560 17.84 1746 NPR 3.9 ps 3.55 2021 华南师范大学 [71] 1211 0.154 1781.5 IM 1.4 μs 3.4 2018 厦门大学 [72] 1560 102 1700 NALM 368 fs 35 2020 西北大学 [73]
1.7 μm波段光纤激光技术研究进展及应用
Progress and applications of 1.7 μm waveband fiber laser
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摘要: 1.7 μm波段有许多分子吸收线, 位于活体组织的透明窗口中。该波段激光源在材料加工、中红外激光产生、气体检测、医疗手术和生物成像等领域有着重要的应用, 受到国内外研究者的重视, 并取得了一些研究成果。总结了国内外1.7 μm波段激光器的研究进展及相关应用, 介绍了长春理工大学在该领域的工作。尽管现有的研究和应用仍面临着一系列问题, 但随着相关技术的不断提高, 1.7 μm波段高性能光纤激光器必将得到快速的发展。Abstract: 1.7 μm waveband covers many molecular absorption lines and is located in the transparent window of living tissue.This band laser source has important applications in material processing, mid infrared laser generation, gas detection, medical surgery, and biological imaging. The research progress and the related applications of 1.7 μm waveband laser were summarized at home and abroad in this paper, and the work of Changchun University of Science and Technology in this field was introduced. Although the research and application of 1.7 μm waveband fiber laser still face a series of problems, it is reasonable to believe that with the continuous improvement of the related technologies, 1.7 μm waveband high-performance fiber laser will develop rapidly.
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Key words:
- laser optics /
- 1.7 μm waveband /
- continuous fiber laser /
- pulsed fiber laser /
- laser application
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表 1 国外1.7 μm波段连续光纤激光器研究进展
Table 1. Research progress in foreign 1.7 μm band continuous fiber laser
技术手段 抽运波长/nm 输出波长/nm 输出功率/mW 效率/% 激光腔型 年份 国家 参考文献 THDF 1565 1706.3 249 23 线性腔 2018 韩国 [37] TDF 1580 1726 47000 80 线性腔 2019 英国 [38] BDF 915 1705 1050 33 线性腔 2018 俄罗斯 [41] BDF 1550 1725,1729 0.6,1.1 — 线性腔 2019 加拿大 [42] 非线性效应 1532~1560 1655,1679 6250,5000 — — 2019 法国 [43] 非线性效应 1540 1650 9250 — — 2019 法国 [44] 表 2 国外1.7 μm波段脉冲激光器研究进展
Table 2. Research progress in foreign 1.7 μm band pulse laser
抽运波长/nm 重复频率/MHz 输出波长/nm 脉冲产生方式 脉冲能量 脉宽 年份 国家 参考文献 1556 232.6~554.6 1735 NPR 21 pJ 630 fs 2016 芬兰 [51] 1030 31 1300~1700 NPR 10.6 nJ 85 fs 2017 德国 [52] 1157 3.57 1700 NALM 84 pJ 17 ps 2018 俄罗斯 [53] 1570 7.82 1785 NALM 128 nJ 174 fs 2020 新加坡 [54] 976 40 1700~2050 非线性效应 1 nJ 150 fs 2019 法国 [55] 1117 — 1700 非线性效应 11.5 mJ~10 J 100 μs~100 ms 2020 丹麦 [56] 1565 5.5 1755 SESAM 32.7 nJ 2.76 ps 2021 新加坡 [57] 表 3 国内1.7 μm波段连续光纤激光器研究进展
Table 3. Research progress in domestic 1.7 μm band continuous fiber laser
技术手段 抽运波长/nm 输出波长/nm 输出功率/W 效率/% 激光腔型 机构 年份 参考文献 THDF 1550 1727~2030 0.408 42.6 环形腔 国防科技大学 2015 [58] TDF 1550 1706.75 3.15 42.1 线性腔 西安光机所 2017 [59] TDF 1570 1720 0.121 5.7 环形腔 天津大学 2020 [60] TDF 1570 1720 2.36 50.2 环形腔 天津大学 2020 [61] TDF 1570 1720 0.407 22.7 环形腔 天津大学 2020 [62] TDF 1570 1720 1.11 46.4 环形腔 天津大学 2020 [63] TDF 976 1720 1.13 13.5 线性腔 天津大学 2020 [64] TGF 1610 1727 0.0124 4.81 线性腔 华南理工大学 2021 [65] 非线性效应 1550 1715 14.5 — 线性腔 国防科技大学 2021 [66] 表 4 国内1.7 μm波段脉冲光纤激光器研究进展
Table 4. Research progress in 1.7 μm band pulse fiber laser in China
抽运波长/nm 重复频率/MHz 输出波长/nm 脉冲产生方式 脉宽 输出功率/mW 年份 机构 参考文献 1600 38.8 1700~1740 非线性效应 200 fs 26.8 2017 上海交通大学 [67] 1540~1550 1 1693~1705 非线性效应 10 ns 1630 2021 国防科技大学 [68] 1540~1550 1.3 1693~1705 非线性效应 13 ns 3300 2021 国防科技大学 [69] 1540 6 1693 非线性效应 30 ns 1500 2021 国防科技大学 [70] 1560 17.84 1746 NPR 3.9 ps 3.55 2021 华南师范大学 [71] 1211 0.154 1781.5 IM 1.4 μs 3.4 2018 厦门大学 [72] 1560 102 1700 NALM 368 fs 35 2020 西北大学 [73] -
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