1.5-μm波段25-GHz重频亚皮秒脉冲输出半导体锁模激光器(特邀)

针对高速光采样、光频梳以及光通信系统应用,研制了1.5μm波段高重频超短脉冲输出半导体锁模激光器.基于AlGaInAs/InP材料体系,采用两段式单片集成锁模结构,引入稀释波导结构,综合降低光限制因子、提升材料饱和能量、降低腔内损耗,从而降低有源区色散对脉冲的影响并提升脉冲峰值功率,最终在1.5μm波段实现了重复频率2...     

级联掺Yb增益光纤提高拍频信号信噪比的实验研究

飞秒光学频率梳的出现使对未知激光的绝对频率测量成为可能,极大地简化了激光绝对频率的量值溯源和比对工作.为了保证测量数值的准确性,飞秒光学频率梳与未知激光的拍频信号fb的信噪比要求大于30 d B.针对碘稳频532 nm激光绝对频率测量的特定需求,以532 nm激光的基频光1064 nm激光的绝对频率测量为着眼点,本文采用303 MHz重复频率的掺Er光纤光学频率梳,首先通过激光放大和光谱展宽技术使光谱覆盖到1μm波段,然后采用级联掺Yb增益光纤技术,将扩谱后1μm波段的激光功率进行放大,提高了掺Er光纤光学频率梳扩谱后1μm波长附近的激光强度.采用碘稳频532 nm激光的基频光作为待测光源与飞秒光学频率梳进行拍频.实验表明,与未经过光谱增强的激光相比,光谱增强后的激光与1064 nm激光拍频信号的信噪比提高了5 d B,保持在35 d B附近.该技术有效地缓解了采用掺Er光纤光梳测量1064 nm激光绝对频率时对直接扩谱所获得的1μm波长激光的强度要求.     

被动高阶谐波锁模掺Er3+光纤激光超短光脉冲的产生及其放大

报道了利用光纤的非线性偏振旋转效应产生可饱和吸收体的锁模机制,从掺Er3+光纤环形腔激光器中产生稳定的高阶谐波锁模光脉冲的实验研究结果(限于示波器带宽,实验中最高曾测量到稳定的4076MHz重复频率的谐波锁模光脉冲).实验中发现有三种不同的演化方式产生高阶谐波锁模光脉冲,还观察到在8352MHz谐波锁模光脉冲的光谱中出现孤子光谱边带.四阶谐波锁模(8352MHz重复频率)超短光脉冲经过6m长高掺杂浓度的掺Er3+光纤放大器放大后产生了平均输出功率1388mW,脉宽201fs,中心波长1531μm,单脉冲能 关键词：     

基于啁啾脉冲放大技术的2W光纤绿光飞秒激光器

绿光波段的飞秒激光一般使用钛蓝宝石飞秒激光器通过倍频产生,但是钛蓝宝石激光器价格高昂,且其固体体制稳定性较差,限制了飞秒绿光激光器的使用范围。采用基于SESAM被动锁模的光纤飞秒种子源和啁啾脉冲放大（Chirped Pulse Amplification,CPA）技术产生1 030 nm的基频光,经过压缩倍频后,实现了脉宽357 fs、平均功率2.187 W的515nm飞秒激光输出。该飞秒激光器具备基频光与倍频光双波长切换输出的能力,且具有体积紧凑、脉冲稳定、转换效率较高、光束质量良好的优势,可作为超快激光加工系统的光源。     

GHz瓦级全固态克尔透镜锁模Yb:CYA飞秒激光器（特邀）

掺镱氯酸钆钙(Yb:CaYAlO₄,简称Yb:CYA)晶体具有生长容易、增益曲线宽广平坦以及比热容高和导热性好等优点,是产生飞秒超短脉冲的优异介质晶体。本文介绍了一种基于Yb:CYA晶体的全固态克尔透镜锁模GHz飞秒振荡器,采用功率为8 W的980 nm光纤激光作为泵浦源,腔型为四镜环形腔结构,Yb:CYA晶体厚度为3 mm。该振荡器能够产生中心波长1 051 nm、平均输出功率1.7 W的GHz飞秒脉冲,脉冲宽度为207 fs。基于Yb:CYA晶体的振荡器实现了GHz重频瓦级飞秒脉冲输出,为进一步基于此振荡器实现高重频飞秒光学频率梳打下了坚实基础。     

高能量掺Yb偏振型大模场面积光子晶体光纤孤子锁模飞秒激光器

实验研究了基于掺Yb偏振型大模场面积光子晶体光纤的孤子锁模激光器,获得了高脉冲能量的飞秒激光输出. 激光器基于线形腔结构,利用光栅对补偿腔内色散,并通过半导体可饱和吸收镜实现锁模的自启动. 实验中从振荡级直接获得了平均功率为700mW, 重复频率为47.3MHz(对应于14.8 nJ的单脉冲能量),脉冲宽度为518 fs的稳定锁模脉冲输出. 与普通孤子锁模飞秒光纤激光器相比,输出的单脉冲能量提高了两个数量级. 关键词： 光子晶体光纤 飞秒 光纤激光器 孤子锁模     

面向Li原子D1线频率测量应用的掺铒飞秒光纤光梳系统

报道了自主研制的面向Li原子D1线频率测量应用的掺铒飞秒光纤光学频率梳,包括飞秒激光源,频率探测及控制单元,光谱展宽及拍频单元.光纤光梳系统中飞秒激光光源是一套基于非线性偏振旋转锁模机制的掺铒飞秒光纤激光器,重复频率为196.5MHz,中心波长为1 572nm.利用f-2f法探测载波包络相移频率,获得信噪比约为40dB的信号(分辨率带宽300kHz).改变飞秒激光光源泵浦控制载波包络相移频率、频率稳定度是3.74×10-18/τ1/2;通过电光晶体和压电陶瓷改变飞秒激光光源腔长来控制重复频率frep、频率稳定度是1.75×10-13/τ1/2.利用高非线性光纤和倍频晶体将光纤光梳直接输出光谱由1 520～1 607nm扩展到671nm,获得了单模功率为208nW的光信号.与671nm单频激光拍频产生约为60dB(分辨率带宽1Hz)信号,满足Li原子D1线频率测量实验的需求.     

303MHz高重复频率掺Er光纤飞秒激光器

高重复频率掺Er光纤飞秒激光器在光学频率梳、超高速光学采样等领域具有很重要的作用. 本文采用非线性偏振旋转锁模机理, 在掺Er光纤飞秒激光器中实现了重复频率为303 MHz的锁模脉冲输出. 通过优化腔内色散, 激光器腔内色散在零色散附近偏负值, 锁模后工作在展宽脉冲锁模状态. 在817 mW抽运功率下, 激光器在连续光状态下可以输出125 mW的平均功率, 在锁模状态下可以输出69 mW的平均功率, 脉冲宽度为90 fs. 当抽运功率处于700-817 mW时, 激光器可以实现自启动锁模. 激光器重复频率在5 h内的漂移量为30 Hz.     

飞秒激光在双折射微结构光纤中模式控制的四波混频效应的实验研究

利用飞秒激光脉冲在长度为10cm，包层具有大空气比的双折射微结构光纤中通过高阶模相位 匹配的四波混频获得了波长可调谐的反斯托克斯波.实验中脉冲宽度为35fs，中心波长820nm ，单脉冲能量4nJ的飞秒激光脉冲耦合到长轴直径为5μm，短轴为46μm的双折射微结构光 纤中.在高阶模传输情况下，通过调制耦合光的偏振方向，获得了具有不同中心波长的反斯 托克斯波.通过对比分析，讨论了输入光的偏振态对双折射微结构光纤中高阶模式下四波混 频效应的影响情况.理论计算分析很好的解释了实验结果. 关键词： 微结构光纤 飞秒脉冲激光 四波混频     

被动高阶谐波锁模掺Er3+光纤激光超短光脉冲的产生及其放大

报道了利用光纤的非线性偏振旋转效应产生可饱和吸收体的锁模机制,从掺Er3+光纤环形腔激光器中产生稳定的高阶谐波锁模光脉冲的实验研究结果(限于示波器带宽,实验中最高曾测量到稳定的407.6 MHz重复频率的谐波锁模光脉冲).实验中发现有三种不同的演化方式产生高阶谐波锁模光脉冲,还观察到在83.52 MHz谐波锁模光脉冲的光谱中出现孤子光谱边带.四阶谐波锁模(83.52 MHz重复频率)超短光脉冲经过6 m长高掺杂浓度的掺Er3+光纤放大器放大后产生了平均输出功率13.88 mW,脉宽201 fs,中心波长1.531 μm,单脉冲能量为0.166 nJ,对应的光脉冲峰值功率0.811×103 W,增益19 dB的放大结果.     

All polarization-maintaining Er:fiber-based optical frequency comb for frequency comparison of optical clocks

We demonstrate an optical frequency comb (OFC) based on a turnkey mode-locked laser with a figure-9-shape structure and polarization-maintaining fibers, for the comparison of frequency among optical clocks with wavelengths of 698 nm, 729 nm, 1068 nm, and 1156 nm. We adopt a multi-branch approach in order to produce high power OFC signals at these specific wavelengths, enabling the signal-to-noise ratio of the beatnotes between the OFC and the clock lasers to exceed 30 dB at a resolution bandwidth of 300 kHz. This approach makes the supercontinuum spectra much easier to be generated than a single branch OFC. However, more out-of-loop fibers degrade the long-term frequency instability due to thermal drift. To minimize the thermal drift effect, we set the fiber lengths of different branches to be similar, and we stabilize the temperature as well. The out-of-loop frequency instability of the OFC due to the incoherence of the multi-branch is about 5.5×10^-19 for 4000 s, while the in-loop frequency instability of f_ceo and that of f_beat are 7.5×10^-18 for 1 s and 8.5×10^-18 for 1 s, respectively. The turnkey OFC meets the requirement for the comparison of frequency between the best optical clocks.     

光梳主动滤波放大实现锶原子光钟二级冷却光源

提出一种结合注入锁定技术的主动滤波放大方法,将光梳直接注入锁定至光栅外腔半导体激光器,产生窄线宽激光光源,该光源可以用于锶原子光钟二级冷却.实验中,将中心波长为689 nm,带宽为10 nm的光梳种子光源注入689 nm光栅式外腔半导体激光器,通过半导体增益光谱与半导体光栅外腔,从飞秒光梳的多个纵模梳齿中挑选出一个纵模模式来进行增益放大,再通过模式竞争,实现单纵模连续光输出;同时,光梳的重复频率锁定在线宽为赫兹量级的698 nm超稳激光光源上,因此,注入锁定后输出的窄线宽激光也继承了超稳激光光源的光谱特性.利用得到的输出功率为12 mW的689 nm窄线宽激光光源实现了88Sr原子光钟的二级冷却过程,最终获得温度为3μK,原子数约为5×10~6的冷原子团.该方法可拓展至原子光钟其他光源的获得,从而实现原子光钟的集成化和小型化.     

Generation of flat optical frequency comb by fiber loop modulation

We propose a novel flat optical frequency comb generation system that employs fiber loop modulation and experimentally demonstrate its operation. Generally, when an external laser beam is injected into a fiber loop system including an optical modulator and an amplifying medium, multiple sidebands are generated exponentially. On the other hand, the fiber loop starts mode-locked oscillation at a center frequency to maximize the round-trip gain in the fiber loop from the seeds of the injected laser sidebands. By locking the sidebands from fiber loop modulation with the mode-locked oscillation in the fiber loop, the synchronous spectrum between the mode-locked oscillation and the sidebands can be shaped into a flat spectrum. Thus, a flat optical frequency comb with a flatness of about ±1 dB is obtained in the spectral bandwidth of about 1 THz.     

光纤型宽带可调连续波差频产生中红外激光器

报道一种新型光纤化宽带可调连续波中红外激光器系统,该激光系统采用准相位匹配(QPM)的差频产生(DFG)技术,非线性晶体为多周期的周期性极化掺镁铌酸锂晶体(PPMgLN),掺镱光纤激光器(YDFL)用作抽运光源,可调激光器经掺铒光纤放大器(EDFA)功率提升后作为信号光源。利用建立的准相位匹配-差频产生系统,获得了连续波中红外差频光输出;实验发现,温度导致相位失谐的半峰全宽(FWHM)为4.5℃;通过优化选择晶体周期,并结合调节信号光波长和控制温度,该准相位匹配-差频产生系统可在3.1~3.6μm内连续调谐。     

光纤型宽带可调连续波差频产生中红外激光器转换效率的研究

以掺镱光纤激光器为抽运源、掺铒光纤激光器后接掺铒光纤放大器为信号源,利用周期极化掺镁铌酸锂晶体,研究了全光纤化差频产生中红外激光器的转换效率特性。结果表明,抽运光和信号光偏振态影响差频产生过程的转换效率,利用偏振控制器,可将抽运光和信号光偏振方向调节到与晶体光轴方向平行,以获得高的转换效率。抽运光和信号光的光束质量既影响差频产生过程的转换效率,又决定晶体纵向位置的容限,当聚焦系统由自聚焦透镜和焦距100mm平凸透镜组成时,相对转换效率达0.717mW-2,晶体纵向位置容限为44mm。此外,差频光在3126.36~3529.6nm范围内调谐时,转换效率基本保持不变。     

Precise determination of characteristic laser frequencies by an Er-doped fiber optical frequency comb

Femtosecond optical frequency combs correlate the microwave and optical frequencies accurately and coherently. Therefore, any optical frequency in visible to near-infrared region can be directly traced to a microwave frequency. As a result, the length unit "meter" is directly related to the time unit "second". This paper validates the capability of the national wavelength standards based on a home-made Er-doped fiber femtosecond optical frequency comb to measure the laser frequencies ranging from visible to near-infrared region. Optical frequency conversion in the femtosecond optical frequency comb is achieved by combining spectral broadening in a highly nonlinear fiber with a single-point frequency-doubling scheme. The signal-to-noise ratio of the beat notes between the femtosecond optical frequency comb and the lasers at 633, 698, 729, 780, 1064, and 1542 nm is better than 30 dB. The frequency instability of the above lasers is evaluated by using a hydrogen clock signal with a instability of better than 1×10^-13 at 1-s averaging time. The measurement is further validated by measuring the absolute optical frequency of an iodine-stabilized 532-nm laser and an acetylene-stabilized 1542-nm laser. The results are within the uncertainty range of the international recommended values. Our results demonstrate the accurate optical frequency measurement of lasers at different frequencies using the femtosecond optical frequency comb, which is not only important for the precise and accurate traceability and calibration of the laser frequencies, but also provides technical support for establishing the national wavelength standards based on the femtosecond optical frequency comb.     

高功率,红光至中红外可调谐腔内和频光学参量振荡器

本文利用高重复频率,高平均功率大模场面积飞秒光纤激光器作为同步抽运源,抽运以多周期极化掺氧化镁铌酸锂为非线性晶体的单共振光学参量振荡器,获得了高功率可调谐红光至中红外光,信号光调谐范围为1450—2200 nm,闲频光调谐范围为2250—4000 nm,在2 W的抽运功率下,信号光输出波长为1502 nm时获得最大输出功率374 mW,转换效率为18.7%,脉冲宽度为144 fs,此时中红外输出中心波长为3.4μm,平均功率为166 mW.再利用BBO晶体对信号光进行腔内和频,获得和频光输出波长调谐范围为610—668 nm,在4.1 W抽运的情况下,最高平均功率为615 nm处的694 mW,转换效率达16.9%.     

单腔双光梳激光器及其光谱学应用研究进展

光频梳因频率等间隔、波长稳定、谱线线宽窄以及谱宽大等特性,在高精度测量和计量中具有广泛的应用。其中,双光梳快速测量包括光谱测量、绝对测距、三维成像和超快异步光学采样等已成为研究热点之一。近年来,基于自由运行的单腔双光梳激光器的双梳光谱学系统由于具有结构简单、测量范围大和精度高等优点而备受关注。首先从时域和频域介绍了光频梳的特性和应用,尤其介绍了双光梳测量的优势,相较目前主流的稳频稳相锁模激光器、电光调制等双光梳光源实现方案,单腔双光梳激光器方案有望避免采用复杂的电子控制系统,简化双光梳光源的结构、体积和成本。因此,重点介绍了波长复用、偏振复用、空间复用和脉冲波形复用的单腔双光梳光纤激光器实现技术,并对其基本原理、性能参数和当前研究的进展以及目前发展中仍然存在的问题进行了分析;同时对保偏光纤双光梳激光器的研究现状及其性能进行了总结。接着,重点介绍了双梳光谱学的测量原理,回顾了现有光谱扩展技术,并详细介绍了基于自由运行的单腔双光梳激光器的双梳光谱学应用案例,包括掺铒光纤激光器所在的近红外波段以及其扩展到中红外和太赫兹波段的光谱探测。最后,总结了目前的单腔双光梳激光器的主要发展趋势,包括进一步提高单腔型双光梳激光腔的重频稳定性、降低共模噪声、探索单腔双光梳系统在中红外以及太赫兹波段的应用,推动单腔双光梳锁模光纤激光器的实用化。     

Phase-locked, erbium-fiber-laser-based frequency comb in the near infrared

A phase-locked frequency comb in the near infrared is demonstrated with a mode-locked, erbium-doped, fiber laser whose output is amplified and spectrally broadened in dispersion-flattened, highly nonlinear optical fiber to span from 1100 to >2200 nm. The supercontinuum output comprises a frequency comb with a spacing set by the laser repetition rate and an offset by the carrier-envelope offset frequency, which is detected with the standard f-to-2f heterodyne technique. The comb spacing and offset frequency are phase locked to a stable rf signal with a fiber stretcher in the laser cavity and by control of the pump laser power, respectively. This infrared comb permits frequency metrology experiments in the near infrared in a compact, fiber-laser-based system.     

Difference frequency generation laser based spectrometers

Tunable mid‐infrared laser sources are the key to precision optical trace gas detection. Difference‐frequency generation (DFG) based laser sources are among a few practical laser sources that have demonstrated ultra‐high detection sensitivities during real‐world applications when combined with appropriate signal enhancing and noise reduction spectroscopic techniques. This article will discuss the technical approaches, illustrate application examples of DFG sources, and offer perspectives to competing technologies.