窄线宽激光技术研究进展(特邀) 下载: 842次创刊六十周年特邀
1 引言
1917年,Einstein[1]在提出“光与物质相互作用”理论时,便预言了受激辐射的存在。美国加利福尼亚州休斯实验室的Maiman[2-3]利用人工合成的红宝石获得波长为694.3 nm的高纯度光源。至此,激光正式进入人们的视野之中。经过六十多年的发展,激光波长[4]、功率[5],以及线宽[6]等参数的性能不断提升,推动了制造业[7]、生命科学[8]、信息技术[9]、科学研究[10-12]等领域的快速发展,激光的科研价值和商业价值早已不言而喻。尤其是近些年,量子通信、相干传感、光学精密测量、引力波探测等技术的突破,对光源的相干长度、功率、噪声等参数提出了更高的要求,窄线宽激光再一次引发了人们的研究热潮。
激光的线宽决定了激光的相干性,线宽压缩技术一直是窄线宽激光领域的研究重点。激光本征线宽源于自发辐射噪声,激光运转过程中受到增益介质自发辐射引起的相位和强度扰动影响,使得激光输出信号的频率存在高斯白噪声,从而引起激光谱线呈现洛伦兹线型的本征展宽[13-14]。此外,环境的振动和温度的改变,也会引起腔长的微弱变化,进而引入经典噪声,激光线宽的变化可用Schawlow-Townes[14-15]公式描述:
式中:vg为光传输的群速度;rf为激光输出端的反射率;h为普朗克常数;ν0为载波频率;Pout为激光输出功率;R为自发辐射速率;L为谐振腔的长度;α为线宽增强因子。在Schawlow-Townes的线宽公式中,决定线宽的主要因素为自发辐射速率R和谐振腔的长度L,其分别与激光的增益介质以及谐振腔结构相关。对于激光的增益介质,无论是稀土离子掺杂光纤还是半导体光放大器,凡是基于受激辐射光放大的增益介质,上能级的能级寿命均是有极限的,自发辐射无法避免。所以,设计合理的腔体结构抑制自发辐射便是压缩激光线宽的主要手段。
为了追求更窄的线宽参数,谐振腔从最开始的主腔型结构不断拓扑与演化。传统的线宽压缩思想认为,激光线宽压缩主要靠提纯主振荡模式频率,提高主振荡模式功率,依靠增益竞争来抑制激光噪声,将激光的增益尽可能集中到经过提纯的主振荡模式中,便可以实现线宽压缩。基于这一思想,超窄滤波、外腔反馈、锁相稳频等一系列线宽压缩技术不断被提出并得到实践。随着激光线宽越来越窄,对超窄带宽滤波器、外腔结构,以及锁相系统的要求越来越高,工艺和成本等因素成为了制约这一思想的主要难题,且诸如主腔激光与反馈外腔的相位匹配、温度变化和机械振动带来的激光相位突变、应用环境中激光波长自锁定等问题也难以解决,制约了这类激光器在恶劣环境下的应用。
如果激光系统能够根据激光的运行状态自动匹配,那么激光便能始终保持最佳的工作状态,如最窄的线宽、最高的功率等,这便是自适应激光构型的核心思想。10余年来,基于自适应分布弱反馈的激光谐振腔架构被提出,它突破了传统激光谐振腔周期性反馈思维的束缚,这种架构具有纯光学反馈、全波段、波长自适应等优点,不同激光器构型模型如
最初始的激光器构型便是单一主腔型激光器,仅有两个反馈截面,它充分体现了激光器结构的三要素,即增益、泵浦和谐振腔。基于这种构型衍生出了很多单腔型谐振腔结构,如空间线形腔或环形腔结构[2,16-17]、超短腔的Fabry-Pérot(F-P)构型激光二极管[18]、环形腔构型的回音壁微腔激光器[19]、光纤结构的线形腔[20-21]或环形腔[22]结构等。根据激光纵模公式,单一主腔结构内会有一系列间隔为c/2nL(环形腔为c/nL)的激光纵模,容易形成多纵模振荡,激光模式会在不同的谐振频率之间跳变,不利于光场的建立和激光的稳定运行。在主腔激光器单反馈面结构的基础上增加一个反馈面,能够增强主振荡模式、延长光子寿命,这便是单外腔反馈型激光构型[23]。主腔与外腔由于物理长度上的差异会产生两组间隔不同的纵模,根据游标效应,只有相位匹配的纵模能够在激光主腔中起振[24],外腔结构增大了激光的纵模间隔、抑制了模式竞争,有利于稳定光场的建立。但是外腔与主腔之间的相位精确匹配困难,容易引起激光相位跳变。再继续增加反馈截面的个数到一个非常大的数量级,形成几百甚至上千个反馈截面的周期性排布,相位以2π的整数进行反馈,这便是分布式布拉格反射(DBR)[25]激光构型,随着反馈面数量的增加以及每个反馈面对于相位的微扰,谐振腔的纵模间隔无限扩大,在增益范围内仅有几个甚至一个起振模式,此时的激光主腔能够形成稳定的光场分布,而稳定的光场分布正是窄线宽激光实现的前提条件之一。将布拉格结构与增益区结合并在布拉格结构中加入定义波长的相移区,这便是分布式反馈(DFB)[25]构型。DFB结构将反馈与放大部分结合在一起,因此结构更加紧凑、集成度更高。相移区的引入进一步限制了光场分布的自由度,这使得DFB结构克服了DBR结构波长漂移和模式跳变的缺陷,运行起来更加稳定。
当谐振反馈截面遍布整个相位周期内时,即在0~2π的相位内分布式反馈并将除主腔外所有的反馈截面的反馈强度降低,这便是波长自适应分布弱反馈构型。波长自适应分布弱反馈激光构型的谐振腔由增益主腔和波长自适应分布弱反馈结构组成,可以理解成一组强反馈面与无数随机弱反馈面。主腔或是强反馈面提供稳定的光场分布,而分布反馈结构或是弱反馈面则为激光主振荡模式服务。在这种新型激光架构中,分布式反馈结构连续不断地向主腔提供微弱反馈,可以抑制自发辐射的时空随机微扰,是一种从无序中创造有序的全新激光运转模式。该结构还具有不限制工作波长、纯光反馈、反馈速度快、不破坏激光的频谱能量分布、线宽压缩比高等优点[26],因此可以对激光线宽进行波长自适应深度压缩。具有分布式反馈特性的光学元器件不断被国内外各单位和课题组提出,应用于激光线宽压缩时也取得了良好的实验结果[27-29]。
2 窄线宽激光器发展脉络
窄线宽激光器发展到如今,激光反馈模式的演变就是激光谐振腔结构的演变。下面按照激光器谐振腔的演变顺序介绍各种构型的窄线宽激光器技术发展现状。
2.1 单一主腔构型
单主腔型激光器从腔型结构上可以分为线形腔和环形腔结构,而从腔长上来划分,又可分为短腔结构和长腔结构。短腔型激光器结构纵模间隔大,如线形腔的F-P结构、环形腔的二维微腔[30]或回音壁微球激光器[19],短腔型激光器本身不需要任何滤波或是模式选择机制便可实现单纵模(SLM)运行,但是会因为光子寿命太短导致本征线宽较宽。长腔结构本身就具有窄线宽特性,如固体激光器、光纤激光器等,但是纵模间隔过小,所以该激光构型的技术难点在于如何实现SLM运行。
2.1.1 线形腔
线形腔,作为激光主腔的经典构型,具有结构简单、效率高、调控容易等优点,历史上第一束真正意义上的激光便是通过线形腔结构得到的,之后其被研究人员不断研究与探索。在DBR与DFB结构诞生之前,线形腔主要以F-P结构为主。随着单频窄线宽激光技术的不断发展,为了实现SLM运行,F-P结构逐渐向着小型化、微型化方向发展,与DBR和DFB结构相比,F-P结构的优势在于工艺更为简单、操作容易。早在1961年,美国的Kotik等[31]就对F-P谐振器中的激光振荡理论进行研究,提出反射镜法线振荡近似的必要条件和充分条件。1985年,美国贝尔实验室提出一种可用于制作窄线宽F-P结构半导体激光器的深刻槽技术[32],之后多家机构不断完善该工艺[33-36],获得了理想的窄线宽激光器输出。刻槽F-P型激光器主体结构为在半导体增益材料上制作的脊形或是矩形波导,在波导的两端通过刻蚀的方式制作沟槽用于反馈,一般使用深刻槽技术直接截断有源层以获得高反射率和低损耗[36],并将倾角引入沟槽,提升激光纵模运行的稳定性[37]。2015年,华中科技大学的奚燕萍教授团队[38]设计了一种倾斜沟槽结构的F-P激光器,如
图 2. 线形主腔激光器。(a)倾斜沟槽结构F-P激光器结构三维视图和俯视图[38];(b)VFR线形腔光纤激光器[41]
Fig. 2. Linear main cavity lasers. (a) Schematic views of the slant trench F-P laser in three dimensions and from above[38]; (b) VFR linear cavity fiber laser[41]
随着光纤器件工艺的发展,尤其是光纤布拉格光栅的制作工艺日渐成熟,线形腔结构在光纤激光器中也得到了广泛应用。1964年,美国光学公司Koester等[39]首次报道了掺钕玻璃光纤对激光的可控强放大作用。1991年,Ball等[40]论述了光纤内布拉格结构对于激光模式的影响以及光纤激光器实现单纵模工作所需的约束条件。目前线形腔结构的光纤激光器除DFB和DBR结构外,都是长腔结构,大多使用FBG[41]、光纤环形镜[21]等光纤器件提供光反馈,也兼具一定的模式选择作用。线形腔结构不得不考虑的一个问题便是空间烧孔效应。在线形腔中,相向传播的光场会发生驻波干涉,导致空间中场强和增益的不均匀分布,而对于热效应比较敏感的光纤材料而言,空间烧孔会引发纤芯内局部的折射率波动,导致模式稳定性降低,激光线宽展宽。在线形腔中抑制空间烧孔的方法主要有两种:改变激光的频率以及改变激光的偏振态。改变激光频率主要通过在激光主腔内加入声光移频器,使得主腔内相向传输的激光由于存在频差而无法发生驻波干涉,但是声光移频器本身固有损耗很高,且不利于激光系统的集成,还会增加激光系统的成本[42]。改变激光偏振态成为了抑制空间烧孔效应的主要方式。一种通过改变偏振态抑制空间烧孔的方法是使主腔中相向传输的激光偏振态互相垂直,可以利用法拉第旋光效应[43]、σ形腔结构[44]等实现。另一种方法是使用扭转模技术将主腔内的激光调整为圆偏振光,从而使主腔内光场强度呈均匀分布。扭转模技术最早是由美国斯坦福大学Evtuhov等[45]提出的,基本原理是在主腔增益介质两侧各插入一个1/4波片,波片光轴与线偏振光的偏振方向成45°角,从而使主腔内相向传播的激光呈现旋转方向相反的圆偏振光。2014年,华南理工大学杨中民教授团队[41]提出一种基于扭转模技术的虚拟折叠环谐振腔(VFR)高集成结构,如
2.1.2 环形腔
环形腔结构是经典线形腔结构的变形,早在1963年,Raytheon公司Tang等[46]便使用环形腔行波场代替线形腔驻波场来提高激光运行的稳定性。随着光纤器件的发展,环形腔光纤激光器由于其灵活的结构设计、全光纤结构而被广泛关注。一般环形腔光纤激光器都为长腔结构,相较于线形腔,环形腔结构不会因驻波产生空间烧孔效应,且长腔结构有利于提高腔内光子寿命,这是超窄激光运行的前提保障。此外,环形腔结构便于引入各类窄带滤波器件,根据选模理论[47],当纵模间隔与窄带滤波器3 dB带宽的比值为0.5~1时,可以有效地消除相邻主腔模式之间的模式竞争,有利于SLM运行,所以大量窄带滤波器件,如饱和吸收体[21-22]、相移光栅[48]、F-P标准具[49-50]、高品质因子(Q值)回音壁(WGM)微腔[51-54]、复合腔滤波器[55-56]等结构被应用于环形腔光纤激光器之中。
饱和吸收体是一种常见的滤波机制。饱和吸收体对光的吸收系数随入射光强增大而减小,当达到饱和值时对激光呈现透明,在谐振腔中,可利用驻波效应增强某一波长激光的强度形成强度相关的自追踪动态光栅,从而实现滤波。基于饱和吸收体的光纤激光器基本结构如
图 3. 环形主腔激光器。(a)基于EYDSF和SA的环形腔光纤激光器[22];(b)使用WGM滤波器的环形腔光纤激光器以及夹在两个棱镜中间的WGM照片[53];(c)光在微球WGM中传播的几何光学描述和模场分布[19];(d)WGM激光系统和高阶激光模式[90]
Fig. 3. Ring main cavity lasers. (a) Ring-cavity fiber laser based on EYDSF and SA[22]; (b) ring-cavity fiber laser using a WGM filter and photograph of WGM sandwiched between two prisms[53]; (c) geometrical-optical description and mode-field distributions of light propagation in a microsphere WGM[19]; (d) the WGM lasing system and the higher-order laser modes[90]
F-P腔、WGM等高品质谐振腔结构的透射光谱具有波长选择特性,自由光谱范围(FSR)更大,可以通过控制谐振腔的Q值合理设计滤波器带宽,实现模式选择。早在1991年,美国加州理工学院Park等[64]便在光纤环形腔内加入光纤F-P滤波器实现了波长可调单纵模激光运行。2014年,德国马克斯-普朗克研究所Collodo等[53]制作了CaF2高Q值WGM微腔,并将其作为环形腔光纤激光器的窄带滤波装置,通过调节偏振控制器保证最佳的耦合模式,实验装置如
除作为窄带滤波器件外,WGM由于高Q值和小模体积等特性,能够显著增强光与物质相互作用,成为实现低阈值和窄线宽激光器的优秀腔体,早在1977年,Ashkin等[65]便提出了在液滴中实现激光激射的想法。制造技术的发展使得用各种材料和形状制造WGM谐振器成为可能。用液滴[65-66]、二氧化硅[67-68]、半导体[69-70]、聚合物[71]等不同的液体和固体材料制成的谐振器已有报道。各种几何形状也不断被提出,微球[72]、圆盘[69,73]、环[74]、环面[67]、圆柱体[70]、锥形[71]已经被证明并应用于光学传感和微腔激光器[75-76]。
早期的WGM谐振腔主要为液滴形,靠液体的强表面张力形成光滑的边界,光被限制在液滴表面,并通过液气界面的全内反射传播,如
由于折射率大,半导体材料可以更好地约束WGM内的激光模式,谐振器的直径可以缩小到几微米。用多种活性材料从半导体微盘/球腔中发出激光已有报道[69,81-85]。除半导体材料外,聚合物材料由于加工容易、结构灵活和成本低等优点,也逐渐被用于WGM激光主腔制作[86-87],而光学晶体材料由于低损耗、高非线性效应和高电光调制系数等优点,更是让其成为WGM激光器的优秀腔体材料[88-89]。2022年,中国科学院上海光学精密机械研究所程亚研究员团队[90]在铌酸锂(LN)微盘上展示了一种独特的单频超窄线宽激光机制,如
2.1.3 非平面环形腔
非平面环形腔(NPRO)激光器是一种特殊的行波场激光构型,通常这种激光器主腔为一整块的晶体,如
图 4. NPRO激光器。(a)NPRO激光器结构图[91];(b)LIGO中基于NPRO的预稳定激光系统[92]
Fig. 4. NPRO laser. (a) NPRO laser structure diagram[91]; (b) the NPRO-based pre-stabilized laser system in LIGO[92]
2.2 单外腔反馈构型
受限于腔长过短、固有损耗大、光子寿命有限、增益介质的自发辐射难以消除等因素,基于腔内反馈的短腔型单腔激光构型线宽加宽,为了解决这一难题,单外腔反馈结构被提出。外腔的作用是延长光子寿命并将经过筛选的光子反馈回主腔,用以优化激光性能、压缩激光线宽[23]。
1975年,Streifer等[99]便研究了外部反馈对激光主腔模式的影响,研究结果表明,反射镜和光栅的相对位置对于确定激光阈值、频率和相对传输功率至关重要,激光纵模对于反馈信号的强度和相位非常敏感。2016年,澳大利亚国立大学Shin等[100]开发了一种稳定的Littrow窄线宽外腔激光器,如
图 5. 外腔激光器机械设计[100]。(a)机械设计;(b)由光纤耦合增益芯片和准直光学元件组成的激光头的隔离剖面图
Fig. 5. Mechanical design of external cavity laser[100]. (a) Mechanical design; (b) isolated section of the laser head consisting of a fiber-coupled gain chip and collimated optics
2.3 DBR激光构型
为了提高激光系统的稳定性,并将波长选择器件集成到主腔结构当中,DBR结构被提出。DBR型谐振腔是基于F-P型谐振腔设计而来的,以周期性的无源布拉格结构代替F-P结构的反射镜提供光反馈。DBR型主腔由于布拉格结构对于激光干涉模式的周期性微扰,本身具有一定的滤波特性,结合短腔结构带来的大纵模间隔很容易实现SLM运行。虽然设计周期性的布拉格结构最初的目的只是为了选择激光波长,但是从腔型的角度来看,这也是单腔结构反馈面增多后的一种表现。DBR结构如
图 6. 典型的DBR和DFB激光器结构[25]。(a)DBR;(b)DFB
Fig. 6. Typical DBR and DFB laser structures[25]. (a) DBR; (b) DFB
2.3.1 半导体DBR激光器
半导体激光器在制作工艺上具有与半导体材料和微纳工艺兼容的天然优势,很多半导体领域的工艺,如二次外延[101-106]、化学气相沉积[107-108]、步进光刻[108-109]、纳米压印[110-111]、电子刻蚀[108,112]、离子刻蚀[109]等都可以直接应用到半导体激光器的研发制作上。20世纪60年代,Hall等[113]最早提出了半导体激光器,并且成功使用砷化镓(GaAs)材料制作了一个P-N同质结半导体激光器。1971年,美国贝尔实验室的Kogelnik等[114]首次提出使用布拉格结构代替反射镜提供反馈的思想,并分析了这种分布式反馈结构的工作原理。2019年,美国加州大学圣芭芭拉分校Huang等[112]设计了一种III-V集成拓展DBR(Extended-DBR)激光器,如
图 7. DBR构型激光器。(a)E-DBR激光器结构[112];(b)DBR光纤激光器结构[121]
Fig. 7. DBR configuration lasers. (a) E-DBR laser configuration[112]; (b) DBR fiber laser configuration[121]
2.3.2 光纤DBR激光器
虽然DBR激光构型很早便被提出,但是受限于早期的光纤加工工艺,直至1988年,南安普敦大学的Jauncey等[115]才报道了首台DBR单频光纤激光器,该激光器在1082 nm处线宽约为1.3 MHz,最大输出功率为0.78 mW。
DBR光纤激光器的发展,依赖于高浓度掺杂光纤制造工艺的发展,如改性化学气相沉积(MCVD)[116]、表面等离子化学气相沉积(SPCVD)[117-118]等技术都可用于制作高浓度掺杂光纤。2020年,中国科学院上海光学精密机械研究所于春雷研究员团队[119]提出了一种基于溶胶凝胶法结合石英管内壁涂覆与熔融拉锥工艺的光纤制备新方案,可制作高掺杂石英光纤。
高掺杂石英光纤[120-121]、多组分光纤(磷酸盐、锗酸盐和铝硅酸盐)[122,123-124]、YAG晶体衍生光纤[125-126]的出现极大地提高了掺杂光纤的增益系数,DBR单频激光器的性能也得到大幅提升。2020年,华南理工大学杨中民教授团队[121]报道了首个波长大于1100 nm的掺钕光纤DBR激光器,其结构如
2.4 DFB激光构型
基于布拉格结构的另一种谐振腔结构便是DFB构型。DFB激光主腔将布拉格结构与有源区相结合,并在结构的中间位置引入相移区,以此来选择激光波长。典型的DFB结构如
2.4.1 DFB半导体激光器
DFB半导体激光器的光栅加工一般有两种方式:1)在有源区利用二次外延和光刻技术生长一组低折射率光栅结构,即二次外延RG-DFB半导体激光器[103,105];2)直接在有源层的表面刻蚀一层光栅结构,即表面光栅SG-DFB半导体激光器[110,128-129]。RG-DFB的优势在于其光栅结构并不会破坏有源层,可以有效降低散射损耗、提高耦合效率,低损耗有利于激光线宽压缩,但是对高阶模式的抑制能力较弱。SG-DFB结构的光栅直接刻蚀在有源区表面或是侧壁上,光模场与光栅结构能够完全耦合,且散射效应可以抑制高阶模式,但是基于不同的有源层材料光栅结构需要专门设计。
1973年,美国加州理工大学Nakamura等[128]利用光泵方式在GaAs材料上制作了第一台DFB激光器,激光波长为0.83 μm。2012年,英国格拉斯哥大学Hou等[103]采用新型外延技术制作侧壁横向布拉格结构,设计了一种横向耦合的1.55 μm DFB激光器,该激光器与弯曲锥形光放大器单片集成,如
图 8. DFB构型激光器。(a)侧壁横向DFB集成激光器原理图和脊波导截面扫描电镜图[103];(b)DFB光纤激光器结构[133]
Fig. 8. DFB configuration lasers. (a) Schematic diagram of the sidewall transverse DFB integrated laser and scanning electron microscopy of the ridge waveguide cross-section[103]; (b) DFB fiber laser structure[133]
2.4.2 DFB光纤激光器
DFB光纤激光器属于短腔结构,想要提升性能一般有两个方向,提高增益光纤的掺杂浓度和改进光纤光栅的刻写技术。目前高浓度石英光纤、多组分光纤等高浓度掺杂光纤已经逐步商品化,但是在掺杂光纤上刻写光栅相对来讲比较困难,比较常用的掺杂光纤刻写技术包括载氢相位掩膜[130]和飞秒加工技术[131]等。世界上第一台DFB光纤激光器由英国南安普敦大学Kringlebotn等[132]在1994年报道。2012年,北京交通大学延凤平教授团队[130]基于MCVD技术制作了单模大有效面积高浓度掺铒光纤,使用载氢相位掩膜技术制备π相移FBG,激光输出功率为43.5 mW,线宽9.8 kHz。2021年,美国Cybell公司Walasik等[133]通过在掺铥光纤内刻写高反射率和低反射率的光栅,设计了一种工作波长在2051 nm和2039 nm的DFB-FBG掺铥光纤激光器,输出线宽为5 kHz,结构如
通过对FBG进行温度、应力控制,还可以实现光纤激光器输出波长的调谐[134]和偏振态切换等[135]。DFB单频光纤激光器通过直接在掺杂光纤上刻写光栅来实现,避免了光纤的熔接,其腔长相对较短,可以实现更稳定的单频运转,但受限于掺杂光纤的光敏性与高泵浦功率下相移光栅的热效应等,DFB单频光纤激光器输出功率相对较低。
2.5 复合反馈外腔构型
DFB与DBR等短腔型主腔激光器受限于腔长,腔内光子寿命不长,线宽很难深度压缩。为了进一步压缩线宽、抑制噪声,这种短主腔型激光构型也常结合外腔结构进行性能优化。而随着光纤器件加工工艺和半导体工艺的发展,外腔反馈结构也逐渐多样化。在光纤器件和波导结构发展起来之前,外腔结构主要以空间光结合分立的光学器件为主,其中,基于光栅的空间外腔反馈结构主要为Littrow[136-138]和Littman[139]结构,如
图 9. Littman和Littrow外腔反馈激光器结构[25]。(a)Littman;(b)Littrow
Fig. 9. Littman and Littrow external cavity feedback laser structures[25]. (a) Littman; (b) Littrow
早在20世纪60年代便有人使用光栅作为外腔反馈器件[144],并分析了光栅结构对于激光的模式选择、波长调谐和线宽压缩特性。国内外多家单位对该结构进行了深入研究[139-140,143,145-147]。此外,基于空间光结构的外腔反馈器件还可以是一系列的光学滤波器件,如F-P标准具[148-149]、声光/电光可调滤波器[150-151]和干涉仪[152]等。这些滤波器件本身具有一定的模式选择能力,可以代替光栅,甚至某些滤波器件,如高Q值的F-P标准具在光谱窄化、线宽压缩方面要优于反射光栅。但是这类器件往往也会面临反馈信号与主腔纵模之间相位匹配的问题。
空间光结构存在着系统冗杂、维护困难等缺陷。随着光纤器件工艺的发展,使用集成化程度更高、鲁棒性更强的光纤波导或光纤器件代替空间光结构是提升激光系统稳定性的有效方案。光纤外腔反馈结构可以是简单的光纤回路反馈[153-154],或是全光纤结构的谐振腔[155]、FBG[156-158]、光纤F-P腔[159-161]和WGM[162-166]等。国内外多家科研单位对这种光纤外腔窄线宽激光器进行了研究[156,158-159,163-164,167-168]。2016年,华南理工大学杨中民教授团队[159]研制了一种基于自注入锁定的超窄线宽全C波段可调谐单频线偏振光纤激光器,如
图 10. 各种外腔反馈型窄线宽激光器。(a)自注入反馈结构光纤激光器[159];(b)使用WGM进行线宽压缩的自注入锁定光纤激光器[163];(c)基于WGM自注入锁定的四波长窄线宽激光阵列[168];(d)Si3N4材料片上外腔反馈激光器[174];(e)光电振荡反馈激光系统[184]
Fig. 10. Various external-cavity feedback narrow linewidth lasers. (a) Self-injection feedback structure fiber laser [159]; (b) self-injection-locked fiber laser with linewidth compression using a WGM [163]; (c) four-wavelength narrow linewidth laser array based on WGM self-injection locking[168]; (d) Si3N4 material on-chip external-cavity feedback laser[174]; (e) photoelectric oscillation feedback laser system[184]
随着微纳加工技术和混合集成技术的成熟,一体化的波导外腔反馈结构窄线宽激光器由于其更小的封装体积、更稳定的性能而被广泛关注。本质上波导外腔反馈还是沿用了光纤结构外腔反馈的相关技术原理,但是半导体材料更加多样,微纳加工技术让激光系统更加紧凑、稳定性更高,这使得波导外腔反馈窄线宽激光器更具实用性。目前常用的光波导材料有Si[147,169-171]、Si3N4[172-175]、III-V族材料[176-177]等。2019年,美国加州大学圣芭芭拉分校Xiang等[174]利用超低损耗氮化硅波导制作了布拉格光栅,如
光电振荡激光构型利用电学负反馈调节主腔,将激光频率锁定到参考源上,如高Q值的谐振腔[178]和冷原子吸收谱线[179]。经过负反馈调谐,激光谐振腔可以根据激光运行状态进行实时匹配。但是电学反馈还是有很多局限性的,如反馈速度慢、伺服系统过于复杂、包含了大量的电路系统等,导致激光系统技术难度大、控制精度高、成本高昂,且系统对于参考源的强依赖特性也使得激光波长被严格限定在某些频点,进一步限制了激光系统的实用性。1983年,基于Pound[180]的微波锁定方法,Drever等[181]首次将光电振荡锁相稳频技术引入激光领域,这项工作也开创了光电振荡激光构型的先河。鉴于3人对此方案的贡献,研究者们将此频率噪声抑制方案命名为PDH法。自此众多研究机构利用精细度日益提高的稳定参考腔[6,28,182-184]将激光稳频的结果不断优化和提升。2017年,德国联邦物理技术研究院(PTB)与实验天体物理联合研究所(JILA)通过两个冷却到124 K的单晶硅F-P超稳腔,将激光线宽压缩到10 mHz,频率不稳定性为4×10-17[6]。国内华东师范大学马龙生教授团队[183]、中国计量科学研究院林弋戈教授团队[182],以及中国科学院国家授时中心张首刚教授团队[184]也将激光频率不稳定性降低到了10-16量级。2020年,中国科学院国家授时中心张首刚教授团队[184]展示了一个基于超低膨胀系数30 cm长超稳腔的激光系统,如
3 波长自适应分布弱反馈窄线宽激光器
上文,本实验组以激光谐振腔的演变发展为线索,对窄线宽光源发展脉络进行了梳理,分析了各种窄线宽激光架构的优势和需要进一步改进的地方,在总结前人工作的基础上,本实验组独立提出了一种新的激光架构,即波长自适应分布弱反馈激光构型,如
图 11. 基于波长自适应分布弱反馈的激光光谱净化原理[188]。(a)波长自适应分布弱反馈激光配置;(b)不同往返时激光相位波动和噪声耦合强度的演变;(c)不同噪声水平下的光谱分布
Fig. 11. Principle of laser spectral purification based on adaptive distributed weak feedback[188]. (a) Adaptive distributed weak feedback laser configuration; (b) evolution of laser phase fluctuation and noise coupling strength at different round trips; (c) spectral distribution at different noise levels
激光线宽展宽主要受到激光系统内部因素和外部因素两方面影响。外部因素主要是环境振动或是温度变化引起的激光腔长的微小改变,进而将环境噪声耦合进激光信号中,导致线宽展宽,这种展宽可以通过优化激光系统的工作环境,或是使用主动反馈技术锁定激光腔长来改善。但是想要进一步深度压缩激光线宽,就要从线宽的本质着手。激光线宽的本质是自发辐射噪声。增益介质的上能级存在着大量能态各异的反转粒子,如果以自发辐射的方式跃迁到下能级,将会辐射出大量不同频率、不同相位,以及不同偏振态的光子,除泵浦受激吸收会激发粒子数反转外,激光能量也会循环往复地与自发辐射进行能量耦合,导致腔内激光频率受到随机干扰,从而出现谱线展宽,这是激光线宽产生的根本原因。抑制自发辐射的最直接的方法便是将不可控的自发辐射转变为可控的受激辐射,这样便可从根源上解决线宽展宽问题。传统的自发辐射抑制方法通过尽量提纯并放大腔内谐振的光信号,以腔内大量运行的高纯度光子来尽可能地激发上能级粒子,进而抑制自发辐射噪声。然而光波是电磁波,具有时空周期性,光波场在谐振腔中的时空分布会影响不同位置处的增益大小,或是对于空间上不同位置上能级粒子的激发能力不同,最典型的现象便是驻波空间烧孔效应。固定驻波场或是行波场对于空间上不同位置能级粒子的激发能力不一样,便会导致部分上能级粒子不能被利用,进而以自发辐射的方式跃迁。为了解决这一问题,本实验组提出了分布式弱反馈思想。首先,利用分布反馈增加激光在腔内的循环时间,降低自发辐射的噪声耦合速率,从而大幅度减小激光的本征线宽;其次,分布式弱反馈可以认为是在时域上对激光相位的连续修饰,因为单个散射点的反馈强度甚至比自发辐射还要弱,它可以避免传统的固定腔反馈所引起的时域相位突变;再次,基于瑞利背向散射的弱反馈信号本身的光谱线宽比泵浦光要窄,可以认为是一种能够连续不断提纯激光信号的自适应窄带滤波器;最后,分布式弱反馈打破了原有激光谐振腔的固定周期结构,对于来自不同反馈截面的光信,以不同的初相位反馈回腔内,在谐振腔中形成“动态驻波”。由于分布式弱反馈强度非常弱,又是随机分布,难以形成稳定的光场分布,不会扰乱激光主腔内的模式振荡,而腔内无处不在的“动态驻波”又可以将主振荡模式难以激发的上能级粒子充分利用,所以分布式弱反馈结构可以深度抑制自发辐射噪声压缩线宽。
3.1 波长自适应分布弱反馈结构中的光谱演化
3.1.1 分布式反馈信号的光谱特性
波长自适应分布弱反馈是基于反馈元件开发的新激光构型,因此研究不同材料、不同结构的反馈元件中的瑞利散射光谱演化非常重要。首先,对一维波导中的弱分布反馈光谱演化规律进行了系统的研究。根据Jaynes-Cummings理论模型[189-191],并考虑反馈结构的耗散[192],建立了一个基于瑞利散射的分布弱反馈光谱演化模型,如
图 12. 分布弱反馈结构光谱演化理论分析[193]。(a)光谱演化模型;(b)瑞利散射谱宽演化过程;(c)瑞利散射谱宽随散射源数量增加的变化趋势
Fig. 12. Principle of spectral evolution of distributed weak feedback structure[193]. (a) Spectral evolution model; (b) Rayleigh scattering spectral width evolution process; (c) Rayleigh scattering spectral width trend with increasing number of scattering sources
为了进一步验证分布式弱反馈的光谱演化规律,采用如
图 13. 分布反馈结构中光谱演化的实验探究[194-195]。(a)实验装置;(b)瑞利散射随泵浦光功率增加的频谱演化;(c)3 dB谱宽变化趋势
Fig. 13. Experimental investigation of spectral evolution in distributed feedback structures[194-195]. (a) Experimental setup; (b) spectral evolution of Rayleigh scattering with increasing pump power; (c) 3 dB spectral width trend
3.1.2 分布式反馈的纵模抑制特性
对于长腔结构的激光系统而言,腔内的模式大多呈现出均匀离散的分布状态,如果没有适合的纵模抑制机制,将很难实现SLM运行。在早期的工作中,本实验组发现分布式反馈在实现线宽压缩的同时,本身也具备模式抑制的能力[195-197]。在随后的研究中,本实验组建立了理论模型来系统分析分布式反馈的模式抑制和光谱净化能力。
分布式弱反馈是一种能够深度压缩激光线宽,而不会有新的纵模产生的理想反馈方式,为了分析分布式弱反馈对于激光纵模的影响,建立了如
图 14. 分布弱反馈机制的理论模型[26]。(a)一维波导结构中有效反馈面分布示意图;(b)Nk个反馈面中相邻平面的光场振幅
Fig. 14. Theoretical model of distributed weak feedback mechanism[26]. (a) Schematic of the distribution of effective feedback planes in one-dimensional waveguide structure; (b) amplitudes at adjacent planes out of a stack of Nk planes
图 15. 分布反馈结构中不同反射系数的频谱演化以及不同反馈面个数的频谱演化[198]。(a)不同反射系数的频谱演化;(b)不同反馈面个数的频谱演化
Fig. 15. Spectrum evolution of different reflection coefficients and spectrum evolution of different feedback surfaces in distributed feedback structure[198]. (a) Spectrum evolution of different reflection coefficients; (b) spectrum evolution of different feedback surfaces
使用相似的模型分析了在激光器振荡过程中,激光纵模的演化过程。激光反馈信号在分布反馈结构中随往返次数的功率频谱演化过程的二维伪彩图如
图 16. 功率频谱演化过程[26]。(a)随往返次数变化频谱演化的二维伪彩图;(b)图16(a)中蓝框对应的局部放大;(c)相同往返时不同波长的频谱演化
Fig. 16. Power spectrum evolution process[26]. (a) Two-dimensional pseudocolor map of the spectra varying with the number of round trips;(b) localized enlargement corresponding to the blue box in Fig. 16(a); (c) spectra of different wavelengths at the same round trips
3.1.3 分布式反馈的线宽深度压缩特性
对分布式反馈线宽压缩特性进行了仿真分析,结果如
图 17. 激光线宽演化的仿真结果[188]。(a)不同反馈系数下激光线宽随反馈长度的演变;(b)不同反馈比下的线宽曲线;(c)(d)随长度和反馈比变化的频谱的二维伪彩色图
Fig. 17. Simulation results of laser linewidth evolution[188]. (a) Laser linewidth evolution with the feedback length under different feedback coefficients; (b) linewidth curve at the different feedback ratios;(c) (d) two-dimensional pseudocolor maps of the spectra varying with the length and with feedback ratio
图 18. 激光线宽自适应压缩过程[188]。(a)(b)瞬态谱和接通反馈时对应的洛伦兹线宽;(c)(d)调谐主激光腔频率时的瞬态光谱和对应的洛伦兹线宽
Fig. 18. Self-adaptive compression process of laser linewidth[188]. (a) (b) Transient spectrum and corresponding Lorentzian linewidth when switching on the feedback; (c) (d) transient spectrum and corresponding Lorentzian linewidth when tuning the frequency of the main laser cavity
按照分布反馈的波长离散性,可以将器件分为连续型分布弱反馈器件和离散型分布弱反馈器件。连续型分布弱反馈器件以各类光纤为主,如单模光纤、拉锥光纤、高数值孔径光纤、高瑞利散射光纤、随机光栅等。其特点是不具备波长选择特性,但可以在任意波长点进行分布弱反馈,是波长自适应的首选反馈器件。离散型分布弱反馈是基于高Q值谐振腔的一种弱分布反馈器件。当注入谐振腔的激光波长恰好处在谐振腔的谐振波长处时,谐振腔内便会累积大量的背向瑞利散射。离散型的分布反馈器件在特定波长处也能够实现线宽的深度压缩,但是这种压缩与谐振波长锁定,无法实现波长自适应,限制了激光器波长调谐和扫频的能力。
3.2 连续型波长自适应分布弱反馈窄线宽激光器
根据前文的理论分析可知,光纤中的随机瑞利散射本身具有抑制纵模、压缩光谱线宽提纯光信号的作用,是绝佳的自适应滤波元件,且分布式反馈构型可以避免传统固定外腔反馈结构引入的激光相位跳变。基于以上优点,自2010年起,本实验组设计了一系列分布式反馈激光系统。
3.2.1 单频超窄线宽激光
基于环形腔结构,本实验组设计了一种使用拉锥光纤累积背向瑞利散射的单频窄线宽光纤激光器结构,如
图 19. 基于分布弱反馈的波长自适应单频光纤激光器[197,200]
Fig. 19. Self-adaptive fiber lasers based on distributed weak feedback[197, 200]
分布式反馈结构具有波长自适应的优势,但是在单频运行时也存在波长漂移的风险。本实验组[201]提出并演示了一种基于稳定环形腔结构分布弱反馈的超窄线宽单频光纤激光器,采用π相移光纤布拉格光栅(PS-FBG)改进了模式选择,实现了SLM运行,然后使用弱分布反馈结构(WDFS)产生的信号进一步压缩线宽,如
图 20. 外腔分布弱反馈超窄线宽单频光纤激光器[201]
Fig. 20. External cavity weak distribution feedback ultra-narrow linewidth single-frequency fiber laser[201]
基于线形腔结构,本实验组早期的方案对于线宽压缩不是很明显[195],之后的工作中,本实验组使用分布式反馈结合短线形腔结构,在实现线宽深度压缩的同时,保证了激光运行的稳定性。2023年,本实验组[202]提出了一种基于分布式外腔反馈的单频DBR光纤激光器线宽深度窄化与控制的新方案,如
图 21. 线宽连续可调分布式反馈外腔DBR光纤激光器[202]
Fig. 21. Continuously linewidth-tunable distributed feedback external cavity DBR fiber laser[202]
基于长光纤波导结构的分布式反馈外腔容易受到外部环境中温度波动和振动引起的热动力学噪声的影响,本实验组不断探索分布式反馈结构的小型化与集成化方案,期待激光器能够拥有更好的稳定性。基于波长自适应分布弱反馈线宽极致压缩的思想,本实验组设计了一种分布式弱反馈芯片外腔结构,与DFB半导体激光器混合集成,如
图 22. 分布式弱反馈芯片外腔[188]。(a)分布式弱反馈芯片外腔结构;(b)拍频信号的频谱对比曲线;(c)具有分布反馈的线宽Lorentz拟合曲线;(d)频率噪声PSD对比曲线;(e)RIN光谱对比曲线,其中,红色曲线表示压缩结果
Fig. 22. Distributed weak feedback chip external cavity[188]. (a) Distributed weak feedback chip external cavity structure; (b) comparison curves of the frequency spectrum from beat frequency signal; (c) Lorentz fitting curve of the linewidth with a distributed feedback; (d) comparison curves of the frequency noise PSD; (e) comparison curves of the RIN spectra, where a red curve indicates the compressed result
3.2.2 波长调谐/波长扫描超窄线宽激光器
波长调谐作为窄线宽光源的功能拓展,具有很重要的应用价值,而分布式反馈结构具有波长自适应特性,当对主腔激光进行连续波长调控时,激光系统仍能实现窄线宽输出,这是目前其他外腔反馈伺服系统无法做到的。基于波长自适应分布反馈的思想,本实验组提出了一系列波长调谐/波长扫描超窄线宽光源。
基于环形腔结构,本实验组提出了如
图 23. 环形腔结构波长调谐/波长扫描超窄线宽激光器[26,196,205-206]
Fig. 23. Ring cavity structure wavelength tuning/wavelength sweeping ultra-narrow linewidth laser[26, 196, 205-206]
在激光快速调谐方面,本实验组基于声致带通光栅(AIFG)结构提出一种宽带快速可调谐光纤激光器,如
基于线形腔结构,本实验组提出了分布式外腔反馈法布里-珀罗光纤激光器结构,如
图 24. 线形腔结构波长调谐超窄线宽激光器[188,207-208]
Fig. 24. Wavelength-tuned ultra-narrow linewidth linear cavity laser [188, 207-208]
3.3 离散型分布弱反馈窄线宽激光器
基于高Q值谐振腔的离散型分布式反馈结构也是自适应分布弱反馈构型向激光系统小型化集成化发展的良好案例。本实验组基于对离散型自适应分布弱反馈器件的研究,设计并研发出系列分布弱反馈超窄线宽激光器,该系列光源拥有小于100 Hz(最小10 Hz)的稳定激光线宽、10 mW的输出功率,以及稳定的运行状态,具体参数如
表 1. 分布弱反馈超窄线宽激光器详细参数
Table 1. Detailed parameters of distributed weak feedback ultra narrow linewidth laser
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3.4 其他基于瑞利弱分布反馈的窄线宽激光器
分布弱反馈具有非常好的线宽压缩和噪声抑制效果,已经得到业内人士的广泛认同,除本课题组外,也有多家单位对此进行了深入研究,如美国OEwaves公司[209]、康奈尔大学[210]、俄罗斯莫斯科物理技术研究所[211-212]、加州大学圣巴巴拉分校[213]等,这些研究机构采用了相似的波长离散型分布弱反馈激光构型,激光系统结构如
图 25. 其他基于分布弱反馈结构的窄线宽激光器[209-216]
Fig. 25. Other narrow linewidth lasers based on distributed weak feedback[209-216]
3.5 超窄线宽测量与表征
对于激光线宽小于kHz的超窄线宽光源参数表征,本实验组[217-218]提出一种基于短光纤延迟线的相干延迟自外差测量方法。当激光相干长度超过延迟自外差系统的延迟光纤长度时,激光线宽的拍频谱表现为非相干洛伦兹型谱线与相干包络谱线的乘积,此时如果延迟光纤长度选取适当,是可以从相干包络谱的峰谷值之差反推激光洛伦兹线宽的,如
图 26. 相干包络法测量激光线宽[217-218]。(a)(b)不同延迟线长度与不同激光线宽归一化功率谱密度;(c)第二峰谷值随激光线宽变化曲线
Fig. 26. Coherent envelope method for measuring laser linewidth[217-218]. (a) (b) Normalized power spectral density for different delay line lengths and different laser linewidths ; (c) second peak-to-valley variation curve with laser linewidth
4 总结与展望
窄线宽激光的发展与应用可以概括为简单的6个字:“窄”“稳”“调”“扫”“测”“用”。回顾窄线宽激光发展的几十年,激光线宽压缩的过程既是激光主腔构型不断演化的过程,又是线宽压缩、噪声抑制思想不断转变与创新的过程。从最初的经典单腔激光主腔构型的单点反馈,到单外腔多点反馈,从DFB、DBR这种固定周期性多点微扰反馈,再到波长自适应分布反馈,不难看出激光噪声抑制和线宽压缩思想始终围绕着激光反馈不断发展与创新。线宽压缩理论的发展与激光主腔结构的不断演化,让窄线宽光源向着线宽更窄、稳定性更高的方向不断发展。而对于线宽压缩来讲,波长自适应分布弱反馈结构无疑是在激光线宽压缩思想上的又一次创新,它打破了原有的激光主腔周期性结构禁锢激光模式的固有思维,以自适应思想使激光主腔来主动匹配和适应激光模式,以达到最佳的激光运行状态。这种“无序产生有序”的调控思想会进一步促进激光参数调控的深入研究。理论上波长自适应分布弱反馈构型可以实现Hz量级以下的窄线宽激光输出,对于激光线宽的压缩以及噪声抑制是一种触底式的极致调控,但是激光系统在外界环境振动和温度变化等影响下还是会出现激光线宽展宽以及性能不稳定等问题。对激光运行环境进行优化,采用精度更高的控温隔振,对具有分布式反馈特性的小型化、集成化光学元器件进行开发,甚至是芯片级波长自适应分布弱反馈激光系统的研发,以提高激光系统的稳定性是这种新激光构型的未来发展方向。另一方面,随着相干通信、传感、密集波分复用系统的快速发展,超窄线宽光源也同样被期待具有波长调谐能力甚至是扫频能力,波长自适应分布弱反馈架构具有反馈速度快和波长自适应的特点,这是现在任何其他激光反馈结构都不具备的优势。在波长精密调控、多波长,以及波长扫描等窄线宽激光拓展方向,波长自适应分布弱反馈架构会更具优势,这将极大拓展超窄线宽激光的应用范围。最后,随着超窄线宽激光参数的极致化发展,与之配套的精确测量和表征方法同样需要革新。总之,超窄线宽光源的发展是一个集开发、表征与应用为一体的过程,只有全面的发展才能满足未来各种科学技术研究和工业发展的需求。
[1] Einstein A. On the quantum mechanics of radiation[J]. Physikalische Zeitschrift, 1917, 18: 121-128.
[2] Maiman T H. Stimulated optical radiation in ruby[J]. Nature, 1960, 187(4736): 493-494.
[3] Maiman T H. Optical and microwave-optical experiments in ruby[J]. Physical Review Letters, 1960, 4(11): 564-566.
[4] Zeng X, Cui S Z, Jiang H W, et al. Single-frequency upconverted laser generation by phase summation[J]. High Power Laser Science and Engineering, 2023, 11: e18.
[5] Wang G J, Song J X, Chen Y S, et al. Six kilowatt record all-fiberized and narrow-linewidth fiber amplifier with near-diffraction-limited beam quality[J]. High Power Laser Science and Engineering, 2022, 10: e22.
[6] LegeroT, MateiD G, HäfnerS, et al. 1.5 μm lasers with sub 10 mHz linewidth[C]∥2017 Conference on Lasers and Electro-Optics (CLEO), May 14-19, 2017, San Jose, CA, USA. New York: IEEE Press, 2017.
[7] 宋威廉. 激光加工技术的发展[J]. 激光与红外, 2006, 36(S1): 755-758.
Song W L. The development of laser processing technology[J]. Laser & Infrared, 2006, 36(S1): 755-758.
[8] Murray K K, Seneviratne C A, Ghorai S. High resolution laser mass spectrometry bioimaging[J]. Methods, 2016, 104: 118-126.
[9] Predehl K, Grosche G, Raupach S M F, et al. A 920-kilometer optical fiber link for frequency metrology at the 19th decimal place[J]. Science, 2012, 336(6080): 441-444.
[10] Uchida A, Amano K, Inoue M, et al. Fast physical random bit generation with chaotic semiconductor lasers[J]. Nature Photonics, 2008, 2(12): 728-732.
[11] Marcu A, Stafe M, Barbuta M, et al. Photon energy transfer on titanium targets for laser thrusters[J]. High Power Laser Science and Engineering, 2022, 10: e27.
[12] 王瑞凤, 张彦朴, 许志艳. 激光技术军事应用的现状及发展趋势[J]. 红外与激光工程, 2007, 36(S1): 308-311.
Wang R F, Zhang Y P, Xu Z Y. Present situation and developing trend of application of laser technique to military[J]. Infrared and Laser Engineering, 2007, 36(S1): 308-311.
[13] Gordon J P, Zeiger H J, Townes C H. The maser: new type of microwave amplifier, frequency standard, and spectrometer[J]. Physical Review, 1955, 99(4): 1264-1274.
[14] Schawlow A L, Townes C H. Infrared and optical masers[J]. Physical Review, 1958, 112(6): 1940-1949.
[15] Henry C. Theory of the linewidth of semiconductor lasers[J]. IEEE Journal of Quantum Electronics, 1982, 18(2): 259-264.
[16] Xie S Y, Bo Y, Xu J L, et al. A high power single frequency diode side-pumped Nd: YAG ring laser[J]. Chinese Physics Letters, 2011, 28(8): 084207.
[17] Wei Y X, Peng W N, Li J W, et al. Self-mode-matching compact low-noise all-solid-state continuous wave single-frequency laser with output power of 140 W[J]. Optics Letters, 2023, 48(3): 676-679.
[18] Jeong Y D, Won Y H, Choi S C, et al. Tunable single-mode Fabry-Perot laser diode using a built-in external cavity and its modulation characteristics[J]. Optics Letters, 2006, 31(17): 2586-2588.
[19] He L N, Özdemir Ş K, Yang L. Whispering gallery microcavity lasers[J]. Laser & Photonics Reviews, 2013, 7(1): 60-82.
[20] Ball G A, Glenn W H. Design of a single-mode linear-cavity erbium fiber laser utilizing Bragg reflectors[J]. Journal of Lightwave Technology, 1992, 10(10): 1338-1343.
[22] Huang J Q, Wen J X, Wan Y, et al. Sub-kHz-linewidth continuous-wave single-frequency ring-cavity fiber laser based on high-gain Er: YAG crystal-derived silica fiber[J]. Optics Express, 2023, 31(4): 5951-5962.
[23] Saito S, Nilsson O, Yamamoto Y. Oscillation center frequency tuning, quantum FM noise, and direct frequency characteristics in external grating loaded semiconductor lasers[J]. IEEE Journal of Quantum Electronics, 1982, 18(6): 961-970.
[24] Kleinman D A, Kisliuk P P. Discrimination against unwanted orders in the Fabry-Perot resonator[J]. Bell System Technical Journal, 1962, 41(2): 453-462.
[25] Lang X K, Jia P, Chen Y Y, et al. Advances in narrow linewidth diode lasers[J]. Science China Information Sciences, 2019, 62(6): 61401.
[26] Dang L Y, Huang L G, Li Y J, et al. A longitude-purification mechanism for tunable fiber laser based on distributed feedback[J]. Journal of Lightwave Technology, 2022, 40(1): 206-214.
[27] Ma W C, Xiong B, Sun C Z, et al. Linewidth narrowing of mutually injection locked semiconductor lasers with short and long delay[J]. Applied Sciences, 2019, 9(7): 1436.
[28] Kessler T, Hagemann C, Grebing C, et al. A sub-40-mHz-linewidth laser based on a silicon single-crystal optical cavity[J]. Nature Photonics, 2012, 6(10): 687-692.
[29] Spirin V V, Bueno Escobedo J L, Korobko D A, et al. Stabilizing DFB laser injection-locked to an external fiber-optic ring resonator[J]. Optics Express, 2020, 28(1): 478-484.
[30] Harayama T, Shinohara S. Two-dimensional microcavity lasers[J]. Laser & Photonics Reviews, 2011, 5(2): 247-271.
[31] Kotik J, Newstein M C. Theory of LASER oscillations in fabry-perot resonators[J]. Journal of Applied Physics, 1961, 32(2): 178-186.
[32] LeeT P, BurrusC A, WiltD P. Spectral linewidth of a variable-gap cleaved-coupled-cavity laser[C]∥Optical Fiber Communication, February 12, 1985, San Diego, California. Washington, DC: OSA, 1985: TUP3.
[33] GruetF, BandiT, MiletiG, et al. Development and spectral characterisation of discrete mode laser diodes (DMLDs) emitting at 780 nm for Rubidium atomic clocks[C]∥2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference (CLEO EUROPE/EQEC), May 22-26, 2011, Munich, Germany. New York: IEEE Press, 2011.
[34] O’Carroll J, Phelan R, Kelly B, et al. Wide temperature range 0
[35] Zou L, Wang L, Yu T T, et al. Wavelength tunable laser based on distributed reflectors with deep submicron slots[J]. Proceedings of SPIE, 2012, 8412: 84120O.
[36] Wang Y, Yang Y G, Zhang S, et al. Narrow linewidth single-mode slotted fabry-Pérot laser using deep etched trenches[J]. IEEE Photonics Technology Letters, 2012, 24(14): 1233-1235.
[37] 姚中辉, 陈红梅, 张子旸. 基于双倾斜沟槽结构的O波段单纵模Fabry-Pérot激光器[J]. 发光学报, 2021, 42(11): 1804-1809.
[38] Li X, Zhu Z S, Xi Y P, et al. Single-mode Fabry-Perot laser with deeply etched slanted double trenches[J]. Applied Physics Letters, 2015, 107(9): 091108.
[39] Koester C J, Snitzer E. Amplification in a fiber laser[J]. Applied Optics, 1964, 3(10): 1182-1186.
[40] Ball G A, Morey W W, Glenn W H. Standing-wave monomode erbium fiber laser[J]. IEEE Photonics Technology Letters, 1991, 3(7): 613-615.
[41] Mo S P, Huang X, Xu S H, et al. 600-Hz linewidth short-linear-cavity fiber laser[J]. Optics Letters, 2014, 39(20): 5818-5821.
[42] Sabert H, Ulrich R. Gain stabilization in a narrow-band optical filter[J]. Optics Letters, 1992, 17(16): 1161-1163.
[43] Takushima Y, Yamashita S, Kikuchi K, et al. Single-frequency and polarization-stable oscillation of Fabry-Perot fiber laser using a nonpolarization-maintaining fiber and an intracavity etalon[J]. IEEE Photonics Technology Letters, 1996, 8(11): 1468-1470.
[44] GuoY Y, WangD J, LiuF L, et al. A novel single-mode, linearly polarized, erbium-doped fiber laser with a stabilized frequency[C]∥2013 International Conference on Computer, Information and Telecommunication Systems (CITS), May 7-8, 2013, Athens, Greece. New York: IEEE Press, 2014.
[45] Evtuhov V, Siegman A E. A “twisted-mode” technique for obtaining axially uniform energy density in a laser cavity[J]. Applied Optics, 1965, 4(1): 142-143.
[46] Tang C L, Statz H, de Mars G. Regular spiking and single-mode operation of ruby laser[J]. Applied Physics Letters, 1963, 2(11): 222-224.
[47] Feng S J, Mao Q H, Tian Y Y, et al. Widely tunable single longitudinal mode fiber laser with cascaded fiber-ring secondary cavity[J]. IEEE Photonics Technology Letters, 2013, 25(4): 323-326.
[48] Suzuki A, Takahashi Y, Yoshida M, et al. An ultralow noise and narrow linewidth λ/4-shifted DFB Er-doped fiber laser with a ring cavity configuration[J]. IEEE Photonics Technology Letters, 2007, 19(19): 1463-1465.
[49] Cheng X P, Shum P, Tse C H, et al. Single-longitudinal-mode erbium-doped fiber ring laser based on high finesse fiber Bragg grating Fabry-Pérot etalon[J]. IEEE Photonics Technology Letters, 2008, 20(12): 976-978.
[50] 白燕, 延凤平, 冯亭, 等. 基于保偏掺铥光纤饱和吸收体的2 μm波段超窄线宽光纤激光器[J]. 中国激光, 2019, 46(1): 0101003.
[51] Kieu K, Mansuripur M. Fiber laser using a microsphere resonator as a feedback element[J]. Optics Letters, 2007, 32(3): 244-246.
[52] Sulaiman A, Harun S W, Ahmad H. Erbium-doped fiber laser with a microfiber coupled to silica microsphere[J]. IEEE Photonics Journal, 2012, 4(4): 1065-1070.
[53] Collodo M C, Sedlmeir F, Sprenger B, et al. Sub-kHz lasing of a CaF2 whispering gallery mode resonator stabilized fiber ring laser[J]. Optics Express, 2014, 22(16): 19277-19283.
[54] Wan H D, Liu L Q, Ding Z Q, et al. Single-longitudinal-mode fiber ring lasers with taper-coupled double-microsphere-cavities[J]. IEEE Photonics Technology Letters, 2017, 29(23): 2123-2126.
[55] Feng T, Wei D, Bi W W, et al. Wavelength-switchable ultra-narrow linewidth fiber laser enabled by a figure-8 compound-ring-cavity filter and a polarization-managed four-channel filter[J]. Optics Express, 2021, 29(20): 31179-31200.
[56] Yang D D, Yan F P, Feng T, et al. Stable narrow-linewidth single-longitudinal-mode thulium-doped fiber laser by exploiting double-coupler-based double-ring filter[J]. Infrared Physics & Technology, 2023, 129: 104568.
[57] Frisken S J. Transient Bragg reflection gratings in erbium-doped fiber amplifiers[J]. Optics Letters, 1992, 17(24): 1776-1778.
[58] Wei F F, Yang X F, Tong Z R, et al. Dual-wavelength narrow-linewidth fiber laser based on F-P fiber ring filter[J]. Optik, 2012, 123(11): 1026-1029.
[59] Havstad S A, Fischer B, Willner A E, et al. Loop-mirror filters based on saturable-gain or-absorber gratings[J]. Optics Letters, 1999, 24(21): 1466-1468.
[60] Shi C D, Fu S J, Shi G N, et al. All-fiberized single-frequency silica fiber laser operating above 2 μm based on SMS fiber devices[J]. Optik, 2019, 187: 291-296.
[61] Horowitz M, Zyskind J, Daisy R, et al. Narrow-linewidth, singlemode erbium-doped fibre laser with intracavity wave mixing in saturable absorber[J]. Electronics Letters, 1994, 30(8): 648-649.
[62] ZhouJ J, LuoA P, LuoZ C, et al. Dual-wavelength single-frequency fiber laser based on graphene saturable absorber[C]∥Asia Communications and Photonics Conference 2014,November 11-14, 2014, Shanghai, China. Washington, DC: OSA, 2014: ATh3A.76.
[63] Chen S Q, Wang Q K, Zhao C J, et al. Stable single-longitudinal-mode fiber ring laser using topological insulator-based saturable absorber[J]. Journal of Lightwave Technology, 2014, 32(22): 4438-4444.
[64] Park N, Dawson J W, Vahala K J, et al. All fiber, low threshold, widely tunable single-frequency, erbium-doped fiber ring laser with a tandem fiber Fabry-Perot filter[J]. Applied Physics Letters, 1991, 59(19): 2369-2371.
[65] Ashkin A, Dziedzic J M. Observation of resonances in the radiation pressure on dielectric spheres[J]. Physical Review Letters, 1977, 38(23): 1351-1354.
[66] Tzeng H M, Wall K F, Long M B, et al. Laser emission from individual droplets at wavelengths corresponding to morphology-dependent resonances[J]. Optics Letters, 1984, 9(11): 499-501.
[67] Min B, Kim S, Okamoto K, et al. Ultralow threshold on-chip microcavity nanocrystal quantum dot lasers[J]. Applied Physics Letters, 2006, 89(19): 191124.
[68] Kippenberg T J, Kalkman J, Polman A, et al. Demonstration of an erbium-doped microdisk laser on a silicon chip[J]. Physical Review A, 2006, 74(5): 051802.
[69] Van Campenhout J, Rojo Romeo P, Regreny P, et al. Electrically pumped InP-based microdisk lasers integrated with a nanophotonic silicon-on-insulator waveguide circuit[J]. Optics Express, 2007, 15(11): 6744-6749.
[70] Reitzenstein S, Heindel T, Kistner C, et al. Low threshold electrically pumped quantum dot-micropillar lasers[J]. Applied Physics Letters, 2008, 93(6): 061104.
[71] Grossmann T, Hauser M, Beck T, et al. High-Q conical polymeric microcavities[J]. Applied Physics Letters, 2010, 96(1): 013303.
[72] Yang L, Vahala K J. Gain functionalization of silica microresonators[J]. Optics Letters, 2003, 28(8): 592-594.
[73] Grossmann T, Schleede S, Hauser M, et al. Direct laser writing for active and passive high-Q polymer microdisks on silicon[J]. Optics Express, 2011, 19(12): 11451-11456.
[74] Lacey S, White I M, Sun Y Z, et al. Versatile opto-fluidic ring resonator lasers with ultra-low threshold[J]. Optics Express, 2007, 15(23): 15523-15530.
[75] Chiasera A, Dumeige Y, Féron P, et al. Spherical whispering-gallery-mode microresonators[J]. Laser & Photonics Reviews, 2010, 4(3): 457-482.
[76] Ward J, Benson O. WGM microresonators: sensing, lasing and fundamental optics with microspheres[J]. Laser & Photonics Reviews, 2011, 5(4): 553-570.
[77] Braginsky V B, Gorodetsky M L, Ilchenko V S. Quality-factor and nonlinear properties of optical whispering-gallery modes[J]. Physics Letters A, 1989, 137(7/8): 393-397.
[78] Lissillour F, Messager D, Stéphan G, et al. Whispering-gallery-mode laser at 1.56 μm excited by a fiber taper[J]. Optics Letters, 2001, 26(14): 1051-1053.
[79] Lin G, Tillement O, Candela Y, et al. Ultra-low threshold lasing in silica whispering-gallery-mode microcavities with Nd3+∶Gd2O3 nanocrystals[J]. Proceedings of SPIE, 2010, 7716: 771622.
[80] Kalkman J, Polman A, Kippenberg T J, et al. Erbium-implanted silica microsphere laser[J]. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions With Materials and Atoms, 2006, 242(1/2): 182-185.
[81] McCall S L, Levi A F J, Slusher R E, et al. Whispering-gallery mode microdisk lasers[J]. Applied Physics Letters, 1992, 60(3): 289-291.
[82] Tamboli A C, Haberer E D, Sharma R, et al. Room-temperature continuous-wave lasing in GaN/InGaN microdisks[J]. Nature Photonics, 2007, 1(1): 61-64.
[83] Yu H M, Su X Q, Pan Y, et al. Narrow linewidth CsPbBr3 perovskite quantum dots microsphere lasers[J]. Optical Materials, 2022, 133: 112907.
[84] Staudinger P, Mauthe S, Triviño N V, et al. Wurtzite InP microdisks: from epitaxy to room-temperature lasing[J]. Nanotechnology, 2021, 32(7): 075605.
[85] Wong W W, Su Z C, Wang N Y, et al. Epitaxially grown InP micro-ring lasers[J]. Nano Letters, 2021, 21(13): 5681-5688.
[86] Grossmann T, Schleede S, Hauser M, et al. Low-threshold conical microcavity dye lasers[J]. Applied Physics Letters, 2010, 97(6): 063304.
[87] Klinkhammer S, Grossmann T, Lüll K, et al. Diode-pumped organic semiconductor microcone laser[J]. IEEE Photonics Technology Letters, 2011, 23(8): 489-491.
[88] Savchenkov A A, Ilchenko V S, Matsko A B, et al. Kilohertz optical resonances in dielectric crystal cavities[J]. Physical Review A, 2004, 70(5): 051804.
[89] Grudinin I S, Matsko A B, Savchenkov A A, et al. Ultra high Q crystalline microcavities[J]. Optics Communications, 2006, 265(1): 33-38.
[91] Kane T J, Byer R L. Monolithic, unidirectional single-mode Nd∶YAG ring laser[J]. Optics Letters, 1985, 10(2): 65-67.
[92] Kwee P, Bogan C, Danzmann K, et al. Stabilized high-power laser system for the gravitational wave detector advanced LIGO[J]. Optics Express, 2012, 20(10): 10617-10634.
[93] Numata K, Yu A W, Camp J B, et al. Laser system development for gravitational-wave interferometry in space[J]. Proceedings of SPIE, 2018, 10511: 105111D.
[94] 臧二军, 曹建平, 李成阳. 半非平面单块固体环形激光器研究[J]. 现代测量与实验室管理, 2004, 12(1): 19-22.
Zang E J, Cao J P, Li C Y. Study on semi-non-planar monolithic solid-state ring laser[J]. China Inspection Body & Laboratory, 2004, 12(1): 19-22.
[95] Yao B Q, Duan X M, Fang D, et al. 7.3 W of single-frequency output power at 2.09 μm from an Ho∶YAG monolithic nonplanar ring laser[J]. Optics Letters, 2008, 33(18): 2161-2163.
[96] 王云祥, 邱琪, 梁旭, 等. 窄线宽低噪声可调谐非平面环形激光器[J]. 红外与激光工程, 2013, 42(3): 595-598.
Wang Y X, Qiu Q, Liang X, et al. Narrow linewidth low noise tunable nonplanar ring lasers[J]. Infrared and Laser Engineering, 2013, 42(3): 595-598.
[97] Lin G P, Cao Y Q, Lu Z H, et al. Spontaneous generation of orbital angular momentum crystals using a monolithic Nd∶YAG nonplanar ring laser[J]. Optics Letters, 2019, 44(2): 203-206.
[98] Cao Y Q, Liu P, Hou C F, et al. Transverse patterns and dual-frequency lasing in a low-noise nonplanar-ring orbital-angular-momentum oscillator[J]. Physical Review Applied, 2020, 13(2): 024067.
[99] Streifer W, Burnham R, Scifres D. Effect of external reflectors on longitudinal modes of distributed feedback lasers[J]. IEEE Journal of Quantum Electronics, 1975, 11(4): 154-161.
[100] Shin D K, Henson B M, Khakimov R I, et al. Widely tunable, narrow linewidth external-cavity gain chip laser for spectroscopy between 1.0-1.1 µm[J]. Optics Express, 2016, 24(24): 27403-27414.
[101] Spiessberger S, Schiemangk M, Wicht A, et al. Narrow linewidth DFB lasers emitting near a wavelength of 1064 nm[J]. Journal of Lightwave Technology, 2010, 28: 2611-2616.
[102] CayronC, TranM, RobertY, et al. Very narrow linewidth of high power DFB laser diode for Cs pumping[C]∥2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference (CLEO EUROPE/EQEC), May 22-26, 2011, Munich, Germany. New York: IEEE Press, 2011.
[103] Hou L P, Haji M, Akbar J, et al. Narrow linewidth laterally coupled 1.55 μm AlGaInAs/InP distributed feedback lasers integrated with a curved tapered semiconductor optical amplifier[J]. Optics Letters, 2012, 37(21): 4525-4527.
[104] Spießberger S, Schiemangk M, Wicht A, et al. DBR laser diodes emitting near 1064 nm with a narrow intrinsic linewidth of 2 kHz[J]. Applied Physics B, 2011, 104(4): 813-818.
[105] MattheyR, GruetF, AffolderbachC, et al. Development and spectral characterisation of ridge DFB laser diodes for Cs optical pumping at 894 nm[C]∥2016 European Frequency and Time Forum (EFTF), April 4-7, 2016, York, UK. New York: IEEE Press, 2016.
[106] WenzelS, BroxO, CasaP D, et al. Ultra-narrow linewidth GaAs-based DBR lasers[C]∥Conference on Lasers and Electro-Optics, May 9-14, 2021, San Jose, California. Washington, DC: Optica Publishing Group, 2021: ATh4G.3.
[107] ColemanJ J, DiasN L, ReddyU. Narrow spectral linewidth surface grating DBR diode lasers[C]∥ISLC 2012 International Semiconductor Laser Conference, October 7-10, 2012, San Diego, CA, USA. New York: IEEE Press, 2012: 173-174.
[108] Belt M, Huffman T, Davenport M L, et al. Arrayed narrow linewidth erbium-doped waveguide-distributed feedback lasers on an ultra-low-loss silicon-nitride platform[J]. Optics Letters, 2013, 38(22): 4825-4828.
[109] Paschke K, Pohl J, Feise D, et al. Properties of 62x nm red-emitting single-mode diode lasers[J]. Proceedings of SPIE, 2014, 9002: 90020A.
[110] DumitrescuM, TelkkalaJ, KarinenJ, et al. Narrow linewidth 894 nm distributed feedback lasers with laterally-coupled ridge-waveguide surface gratings fabricated using nanoimprint lithography[C]∥CAS 2010 Proceedings (International Semiconductor Conference), October 11-13, 2010, Sinaia, Romania. New York: IEEE Press, 2010: 131-141.
[111] Virtanen H, Uusitalo T, Karjalainen M, et al. Narrow-linewidth 780-nm DFB lasers fabricated using nanoimprint lithography[J]. IEEE Photonics Technology Letters, 2018, 30(1): 51-54.
[112] HuangD N, TranM A, GuoJ, et al. Sub-kHz linewidth Extended-DBR lasers heterogeneously integrated on silicon[C]∥Optical Fiber Communication Conference (OFC) 2019, October 11-13, 2010, San Diego, California. Washington, D.C.: OSA, 2019: W4E.4.
[113] Hall R N, Fenner G E, Kingsley J D, et al. Coherent light emission from GaAs junctions[J]. Physical Review Letters, 1962, 9(9): 366-368.
[114] Kogelnik H, Shank C V. Stimulated emission in a periodic structure[J]. Applied Physics Letters, 1971, 18(4): 152-154.
[115] Jauncey I M, Reekie L, Townsend J E, et al. Single-longitudinal-mode operation of an Nd3+-doped fibre laser[J]. Electronics Letters, 1988, 24(1): 24-26.
[116] Nagel S, MacChesney J, Walker K. An overview of the modified chemical vapor deposition (MCVD) process and performance[J]. IEEE Journal of Quantum Electronics, 1982, 18(4): 459-476.
[117] Barnini A, Robin T, Cadier B, et al. Rare-earth-doped optical-fiber core deposition using full vapor-phase SPCVD process[J]. Proceedings of SPIE, 2017, 10100: 101000D.
[118] Alexandre B, Kilian Le C, Louanne K, et al. Low numerical aperature large-mode-area neodymium-doped fibers fabricated by SPCVD and ASD for laser operation near 920 nm[J]. Proceedings of SPIE, 2020, 11276: 112760L.
[119] Xia L S, Wang M, Kuan P W, et al. Paving way for fabrication of silica-based single-frequency seed laser: Ultrahighly Yb-doped optical fibers via sol-gel method combined with silica tube inner wall coating and fusion-tapering technique[J]. Optics & Laser Technology, 2020, 131: 106425.
[120] Fang Q, Xu Y, Fu S J, et al. Single-frequency distributed Bragg reflector Nd doped silica fiber laser at 930 nm[J]. Optics Letters, 2016, 41(8): 1829-1832.
[121] Wang Y F, Wu J M, Zhao Q L, et al. Single-frequency DBR Nd-doped fiber laser at 1120 nm with a narrow linewidth and low threshold[J]. Optics Letters, 2020, 45(8): 2263-2266.
[123] Zhu X S, Zong J E, Miller A, et al. Single-frequency Ho3+-doped ZBLAN fiber laser at 1200 nm[J]. Optics Letters, 2012, 37(20): 4185-4187.
[124] Xu S H, Yang Z M, Liu T, et al. An efficient compact 300 mW narrow-linewidth single frequency fiber laser at 1.5 μm[J]. Optics Express, 2010, 18(2): 1249-1254.
[125] Liu Z J, Xie Y Y, Cong Z H, et al. 110 mW single-frequency Yb: YAG crystal-derived silica fiber laser at 1064 nm[J]. Optics Letters, 2019, 44(17): 4307-4310.
[127] Cen X, Guan X C, Yang C S, et al. Short-wavelength, in-band-pumped single- frequency DBR Tm3+-doped germanate fiber laser at 1.7 μm[J]. IEEE Photonics Technology Letters, 2021, 33(7): 350-353.
[128] Nakamura M, Yariv A, Yen H W, et al. Optically pumped GaAs surface laser with corrugation feedback[J]. Applied Physics Letters, 1973, 22(10): 515-516.
[129] Hai Y N, Zou Y G, Ma X H, et al. Narrow-linewidth surface-emitting distributed feedback semiconductor lasers with low threshold current[J]. Optics & Laser Technology, 2021, 135: 106631.
[130] Li Q, Yan F P, Peng W J, et al. DFB laser based on single mode large effective area heavy concentration EDF[J]. Optics Express, 2012, 20(21): 23684-23689.
[131] Bernier M, Michaud-Belleau V, Levasseur S, et al. All-fiber DFB laser operating at 2.8 μm[J]. Optics Letters, 2014, 40(1): 81-84.
[132] Kringlebotn J T, Archambault J L, Reekie L, et al. Er3+∶Yb3+-codoped fiber distributed-feedback laser[J]. Optics Letters, 1994, 19(24): 2101-2103.
[133] Walasik W, Traoré D, Amavigan A, et al. 2-μm narrow linewidth all-fiber DFB fiber Bragg grating lasers for Ho- and Tm-doped fiber-amplifier applications[J]. Journal of Lightwave Technology, 2021, 39(15): 5096-5102.
[134] Ball G A, Morey W W. Continuously tunable single-mode erbium fiber laser[J]. Optics Letters, 1992, 17(6): 420-422.
[135] Tao Y, Zhang S, Jiang M, et al. High power and high efficiency single-frequency 1030 nm DFB fiber laser[J]. Optics & Laser Technology, 2022, 145: 107519.
[136] Li B, Gao J, Yu A L, et al. 500 mW tunable external cavity diode laser with narrow line-width emission in blue-violet region[J]. Optics & Laser Technology, 2017, 96: 176-179.
[137] Bayrakli I. Investigation of double-mode operation and fast fine tuning properties of a grating-coupled external cavity diode laser configuration[J]. Optics & Laser Technology, 2017, 87: 7-10.
[138] Ding D, Lü X Q, Chen X Y, et al. Tunable high-power blue external cavity semiconductor laser[J]. Optics & Laser Technology, 2017, 94: 1-5.
[139] Chen D J, Fang Z J, Cai H W, et al. Polarization characteristics of an external cavity diode laser with littman-metcalf configuration[J]. IEEE Photonics Technology Letters, 2009, 21(14): 984-986.
[140] Wang Y, Zhou Y L, Wu H, et al. A tunable external cavity laser operating at excited states of bimodal-sized quantum-dot[J]. Japanese Journal of Applied Physics, 2019, 58(5): 051013.
[141] Podoskin A, Golovin V, Gavrina P, et al. Ultrabroad tuning range (100 nm) of external-cavity continuous-wave high-power semiconductor lasers based on a single InGaAs quantum well[J]. Applied Optics, 2019, 58(33): 9089-9093.
[142] Shirazi M F, Kim P, Jeon M, et al. Free space broad-bandwidth tunable laser diode based on Littman configuration for 3D profile measurement[J]. Optics & Laser Technology, 2018, 101: 462-467.
[143] Kapasi D P, Eichholz J, McRae T, et al. Tunable narrow-linewidth laser at 2 μm wavelength for gravitational wave detector research[J]. Optics Express, 2020, 28(3): 3280-3288.
[144] Hard T M. Laser wavelength selection and output coupling by a grating[J]. Applied Optics, 1970, 9(8): 1825-1830.
[145] Wang Y, Luo S, Ji H M, et al. Continuous-wave operation of InAs/InP quantum dot tunable external-cavity laser grown by metal-organic chemical vapor deposition[J]. Chinese Physics B, 2021, 30(1): 018106.
[146] Jiang Y F, Vijayraghavan K, Jung S, et al. External cavity terahertz quantum cascade laser sources based on intra-cavity frequency mixing with 1.2‒5.9 THz tuning range[J]. Journal of Optics, 2014, 16(9): 094002.
[147] Ojanen S P, Viheriälä J, Cherchi M, et al. GaSb diode lasers tunable around 2.6 μm using silicon photonics resonators or external diffractive gratings[J]. Applied Physics Letters, 2020, 116(8): 081105.
[148] ZhangX M, WangN, GaoL, et al. Narrow-linewidth external-cavity tunable lasers[C]∥10th International Conference on Optical Communications and Networks (ICOCN 2011), November 5-7, 2011, Guangzhou, China. London: IET, 2011: 1-3.
[149] Dahmani B, Hollberg L, Drullinger R. Frequency stabilization of semiconductor lasers by resonant optical feedback[J]. Optics Letters, 1987, 12(11): 876-878.
[150] Gambell A, Simakov N, Ganija M, et al. Intra-cavity semiconductor laser tuning using a frequency compensating acousto-optic tunable filter pair[J]. Proceedings of SPIE, 2019, 11200: 1120027.
[151] Ménager L, Cabaret L, Lorgeré I, et al. Diode laser extended cavity for broad-range fast ramping[J]. Optics Letters, 2000, 25(17): 1246-1248.
[152] Pan G Z, Guan B L, Xu C, et al. Broad bandwidth interference filter-stabilized external cavity diode laser with narrow linewidth below 100 kHz[J]. Chinese Physics B, 2018, 27(1): 014204.
[153] Zhao Y J, Wang Q P, Chang J, et al. Linewidth narrowing and polarization control of erbium-doped fiber laser by self-injection locking[J]. Laser Physics, 2011, 21(12): 2108-2111.
[154] Zhao Y J, Wang Q P, Chang J, et al. Suppression of the intensity noise in distributed feedback fiber lasers by self-injection locking[J]. Laser Physics Letters, 2012, 9(10): 739-743.
[155] Hao L Y, Wang X H, Jia K P, et al. Narrow-linewidth single-polarization fiber laser using non-polarization optics[J]. Optics Letters, 2021, 46(15): 3769-3772.
[156] Zhang L, Wei F, Sun G W, et al. Thermal tunable narrow linewidth external cavity laser with thermal enhanced FBG[J]. IEEE Photonics Technology Letters, 2017, 29(4): 385-388.
[157] Wang Z K, Shang J M, Xu Y F, et al. Stable narrow-linewidth single-longitudinal mode laser by exploiting double subring resonator and self-injection loop[J]. Optical Fiber Technology, 2022, 68: 102775.
[158] Congar A, Gay M, Perin G, et al. Narrow linewidth near-UV InGaN laser diode based on external cavity fiber Bragg grating[J]. Optics Letters, 2021, 46(5): 1077-1080.
[159] Zhang Y N, Zhang Y F, Zhao Q L, et al. Ultra-narrow linewidth full C-band tunable single-frequency linear-polarization fiber laser[J]. Optics Express, 2016, 24(23): 26209-26214.
[161] Wei F, Yang F, Zhang X, et al. Subkilohertz linewidth reduction of a DFB diode laser using self-injection locking with a fiber Bragg grating Fabry-Perot cavity[J]. Optics Express, 2016, 24(15): 17406-17415.
[162] Dale E, Bagheri M, Matsko A B, et al. Microresonator stabilized 2 μm distributed-feedback GaSb-based diode laser[J]. Optics Letters, 2016, 41(23): 5559-5562.
[163] Jiang L D, Shi L L, Luo J, et al. Narrow linewidth VCSEL based on resonant optical feedback from an on-chip microring add-drop filter[J]. Optics Letters, 2021, 46(10): 2320-2323.
[164] Jiang L D, Shi L L, Luo J, et al. Simultaneous self-injection locking of two VCSELs to a single whispering-gallery-mode microcavity[J]. Optics Express, 2021, 29(23): 37845-37851.
[165] Ji J R, Wang H T, Ma J E, et al. Narrow linewidth self-injection locked fiber laser based on a crystalline resonator in add-drop configuration[J]. Optics Letters, 2022, 47(6): 1525-1528.
[166] Lai Y H, Eliyahu D, Ganji S, et al. 780 nm narrow-linewidth self-injection-locked WGM lasers[J]. Proceedings of SPIE, 2020, 11266: 112660O.
[167] Yang X, Lindberg R, Margulis W, et al. Continuously tunable, narrow-linewidth laser based on a semiconductor optical amplifier and a linearly chirped fiber Bragg grating[J]. Optics Express, 2019, 27(10): 14213-14220.
[168] Shi L L, Luo J, Jiang L D, et al. Narrow linewidth semiconductor multi-wavelength DFB laser array simultaneously self-injection locked to a single microring resonator[J]. Optics Letters, 2023, 48(8): 1974-1977.
[169] Chu T, Fujioka N, Compact Ishizaka M.. lower-power-consumption wavelength tunable laser fabricated with silicon photonic-wire waveguide micro-ring resonators[J]. Optics Express, 2009, 17(16): 14063-14068.
[170] Guan H, Novack A, Galfsky T, et al. Widely-tunable, narrow-linewidth III-V/silicon hybrid external-cavity laser for coherent communication[J]. Optics Express, 2018, 26(7): 7920-7933.
[171] Zheng W H, Dong F X, Liu A J, et al. Design of double-ring resonator for tunable lasers on silicon[J]. Proceedings of SPIE, 2017, 10460: 104601R.
[172] Dass D, Costas M T, Barry L P, et al. 28 GBd PAM-8 transmission over a 100 nm range using an InP-Si3N4 based integrated dual tunable laser module[J]. Optics Express, 2021, 29(11): 16563-16571.
[173] Lin Y, Browning C, Timens R B, et al. Characterization of hybrid InP-TriPleX photonic integrated tunable lasers based on silicon nitride (Si3N4/SiO2) microring resonators for optical coherent system[J]. IEEE Photonics Journal, 2018, 10(3): 1400108.
[174] Xiang C, Morton P A, Bowers J E. Ultra-narrow linewidth laser based on a semiconductor gain chip and extended Si3N4 Bragg grating[J]. Optics Letters, 2019, 44(15): 3825-3828.
[175] Guo J, McLemore C A, Xiang C, et al. Chip-based laser with 1-hertz integrated linewidth[J]. Science Advances, 2022, 8(43): eabp9006.
[176] Han Y, Zhang X, Huang F J, et al. Electrically pumped widely tunable O-band hybrid lithium niobite/III-V laser[J]. Optics Letters, 2021, 46(21): 5413-5416.
[177] Li M X, Chang L, Wu L, et al. Integrated pockels laser[J]. Nature Communications, 2022, 13: 5344.
[178] Bayrakli I. Frequency stabilization at the sub-kilohertz level of an external cavity diode laser[J]. Applied Optics, 2016, 55(9): 2463-2466.
[179] Stack D T, Lee P J, Quraishi Q. Simple and efficient absorption filter for single photons from a cold atom quantum memory[J]. Optics Express, 2015, 23(5): 6822-6832.
[180] Pound R V. Electronic frequency stabilization of microwave oscillators[J]. Review of Scientific Instruments, 1946, 17(11): 490-505.
[181] Drever R W P, Hall J L, Kowalski F V, et al. Laser phase and frequency stabilization using an optical resonator[J]. Applied Physics B, 1983, 31(2): 97-105.
[183] Jin L, Jiang Y Y, Yao Y, et al. Laser frequency instability of 2×10-16 by stabilizing to 30-cm-long Fabry-Pérot cavities at 578 nm[J]. Optics Express, 2018, 26(14): 18699-18707.
[184] JiangC H, ZhangL B, ChenL, et al. Research progress of an ultra-stable laser system stabilized to a 30-cm-long cavity at NTSC[C]∥2020 IEEE 5th Optoelectronics Global Conference (OGC), September 7-11, 2020, Shenzhen, China. New York: IEEE Press, 2020: 87-89.
[185] Bu J Y, Jiao D D, Xu G J, et al. Fast auto-relock methods for ultra-stable lasers[J]. Infrared Physics & Technology, 2023, 134: 104915.
[186] Weel M, Kumarakrishnan A. Laser-frequency stabilization using a lock-in amplifier[J]. Canadian Journal of Physics, 2002, 80(12): 1449-1458.
[187] Shaddock D A, Gray M B, McClelland D E. Frequency locking a laser to an optical cavity by use of spatial mode interference[J]. Optics Letters, 1999, 24(21): 1499-1501.
[189] Zheng S B. Jaynes-Cummings model with a collective atomic mode[J]. Physical Review A, 2008, 77(4): 045802.
[190] Romanelli A. Generalized Jaynes-Cummings model as a quantum search algorithm[J]. Physical Review A, 2009, 80(1): 014302.
[191] Peano V, Thorwart M. Quasienergy description of the driven Jaynes-Cummings model[J]. Physical Review B, 2010, 82(15): 155129.
[192] Chen Q H, Liu T, Zhang Y Y, et al. Exact solutions to the Jaynes-Cummings model without the rotating-wave approximation[J]. EPL (Europhysics Letters), 2011, 96(1): 14003.
[193] Li F H, Lan T Y, Huang L G, et al. Spectrum evolution of Rayleigh backscattering in one-dimensional waveguide[J]. Opto-Electronic Advances, 2019, 2(8): 190012.
[194] Zhu T, Bao X Y, Chen L, et al. Experimental study on stimulated Rayleigh scattering in optical fibers[J]. Optics Express, 2010, 18(22): 22958-22963.
[195] Zhu T, Bao X Y, Chen L. A self-gain random distributed feedback fiber laser based on stimulated Rayleigh scattering[J]. Optics Communications, 2012, 285(6): 1371-1374.
[196] Zhu T, Bao X Y, Chen L. A single longitudinal-mode tunable fiber ring laser based on stimulated Rayleigh scattering in a nonuniform optical fiber[J]. Journal of Lightwave Technology, 2011, 29(12): 1802-1807.
[197] Zhu T, Chen F Y, Huang S H, et al. An ultra-narrow linewidth fiber laser based on Rayleigh backscattering in a tapered optical fiber[J]. Laser Physics Letters, 2013, 10(5): 055110.
[198] Dang L Y, Huang L G, Cao Y L, et al. Side mode suppression of SOA fiber hybrid laser based on distributed self-injection feedback[J]. Optics & Laser Technology, 2022, 147: 107619.
[199] Li F H, Lan T Y, Ikechukwu I P, et al. Experimental study on linewidth compression based on Rayleigh backscattering in 1064 nm fiber laser[J]. Optics Communications, 2019, 430: 268-272.
[200] Zhu T, Huang S H, Shi L L, et al. Rayleigh backscattering: a method to highly compress laser linewidth[J]. Chinese Science Bulletin, 2014, 59(33): 4631-4636.
[201] Dang L Y, Zhang C Z, Zheng B W, et al. Tens of hertz ultra-narrow linewidth fiber ring laser based on external weak distributed feedback[J]. Optics Express, 2022, 30(19): 34575-34585.
[202] Dang L Y, Zhang C Z, Li J L, et al. Spectrum extreme purification and modulation of DBR fiber laser with weak distributed feedback[J]. Journal of Lightwave Technology, 2023, 41(16): 5437-5444.
[203] Dang L Y, Li J L, Wei D, et al. Linewidth depth narrowing and control of linear cavity fiber laser based on distributed external feedback[J]. Proceedings of SPIE, 2023, 12595: 1259506.
[204] Li Y J, Huang L G, Gao L, et al. Optically controlled tunable ultra-narrow linewidth fiber laser with Rayleigh backscattering and saturable absorption ring[J]. Optics Express, 2018, 26(21): 26896-26906.
[205] Li Y J, Dang L Y, Huang L G, et al. Tunable narrow-linewidth fiber laser based on the acoustically controlled polarization conversion in dispersion compensation fiber[J]. Journal of Lightwave Technology, 2022, 40(9): 2971-2979.
[206] Li Y J, Dang L Y, Huang L G, et al. Tuning dynamics of the acousto-optical tunable SOA fiber laser[J]. Journal of Lightwave Technology, 2022, 40(17): 5967-5973.
[207] Dang L Y, Zheng B W, Cao Y L, et al. Tunable ultra-narrow linewidth linear-cavity fiber lasers assisted by distributed external feedback[J]. Optics & Laser Technology, 2023, 166: 109529.
[208] Jiang L D, Lan T Y, Dang L Y, et al. Ultra-narrow linewidth vertical-cavity surface-emitting laser based on external-cavity weak distributed feedback[J]. Optics Express, 2022, 30(21): 37519-37525.
[209] Liang W, Ilchenko V S, Eliyahu D, et al. Ultralow noise miniature external cavity semiconductor laser[J]. Nature Communications, 2015, 6: 7371.
[210] Stern B, Ji X C, Dutt A, et al. Compact narrow-linewidth integrated laser based on a low-loss silicon nitride ring resonator[J]. Optics Letters, 2017, 42(21): 4541-4544.
[211] Pavlov N G, Koptyaev S, Lihachev G V, et al. Narrow-linewidth lasing and soliton Kerr microcombs with ordinary laser diodes[J]. Nature Photonics, 2018, 12(11): 694-698.
[212] Chermoshentsev D A, Shitikov A E, Lonshakov E A, et al. Dual-laser self-injection locking to an integrated microresonator[J]. Optics Express, 2022, 30(10): 17094-17105.
[213] Jin W, Yang Q F, Chang L, et al. Hertz-linewidth semiconductor lasers using CMOS-ready ultra-high-Q microresonators[J]. Nature Photonics, 2021, 15(5): 346-353.
[214] Skvortsov M I, Wolf A A, Dostovalov A V, et al. Narrow-linewidth Er-doped fiber lasers with random distributed feedback provided by artificial Rayleigh scattering[J]. Journal of Lightwave Technology, 2021, 40(6): 1829-1835.
[215] Skvortsov M I, Abdullina S R, Podivilov E V, et al. Extreme narrowing of the distributed feedback fiber laser linewidth due to the Rayleigh backscattering in a single-mode fiber: model and experimental test[J]. Photonics, 2022, 9(8): 590.
[216] Feng T, Su J, Wei D, et al. Effective linewidth compression of a single-longitudinal-mode fiber laser with randomly distributed high scattering centers in the fiber induced by femtosecond laser pulses[J]. Optics Express, 2023, 31(3): 4238-4252.
[217] Huang S H, Zhu T, Liu M, et al. Precise measurement of ultra-narrow laser linewidths using the strong coherent envelope[J]. Scientific Reports, 2017, 7: 41988.
[218] Huang S H, Zhu T, Cao Z Z, et al. Laser linewidth measurement based on amplitude difference comparison of coherent envelope[J]. IEEE Photonics Technology Letters, 2016, 28(7): 759-762.
Article Outline
朱涛, 韦达, 史磊磊, 黄礼刚, 李嘉丽, 徐敏志. 窄线宽激光技术研究进展(特邀)[J]. 激光与光电子学进展, 2024, 61(1): 0114003. Tao Zhu, Da Wei, Leilei Shi, Ligang Huang, Jiali Li, Minzhi Xu. Research Progress in Narrow Linewidth Laser Technology (Invited)[J]. Laser & Optoelectronics Progress, 2024, 61(1): 0114003.