高掺杂浓度掺镱光纤的光子暗化效应

采用光纤激光器和放大器结构方案，观察到了高浓度掺镱光纤（YDF）的光子暗化（Photo-darkening）现象.对激光器阈值和输出功率、放大器输出谱的测量结果表明，光子暗化效应导致了高掺杂浓度YDF的功率转换效率随泵浦作用时间的增加而下降，且下降为单调不可逆过程，但随着泵浦时间的增加，这种下降逐渐变缓、功率转换效率最终可趋于稳定.     

128 W单频线偏振光纤放大器特性研究

高功率单频激光在激光雷达、光谱学、精密测量等领域具有广阔的应用前景.采用中心波长为1064 nm、光谱线宽为20 kHz、偏振消光比（PER）高于20 dB的单频线偏振分布式反馈光纤激光器做种子源（尾纤输出功率约为10 mW）,利用种子注入主振荡功率光纤放大技术,通过两级级联放大实现了128 W高功率单频、线偏振、近衍射极限单模连续激光输出.主放大器光-光效率达到83%,PER高于12 dB.采用分段温控技术有效地提高了光纤中的受激布里渊散射（SBS）阈值,实验中未观察到明显的放大自发辐射和SBS现象,进 关键词： 掺Yb光纤放大器 主振荡功率光纤放大 单频 线偏振     

基于少模光纤被动调Q柱矢量光光纤激光器

通过单模光纤和少模光纤熔融拉锥耦合的方法制备出模式转换器,而后将一层多壁的碳纳米管薄膜作为可饱和吸收体覆盖到拉锥光纤的锥区,形成一种可饱和吸收体柱矢量光器件.结合调Q光纤激光器和模式转换器件的优势,可以简单高效地产生脉冲柱矢量光束,并得到具有峰值功率高、模式纯度高等特点的脉冲高阶模式激光输出.通过实验实现了中心波长为1560nm、最大单脉冲能量和最大峰值功率分别为116nJ和57mW的稳定调Q脉冲输出.通过调节光路中的偏振控制器,可以分别实现径向和角向偏振的调Q脉冲激光的输出.     

Specific mode output from multimode fiber oscillators by designing rare earth doping profiles

Based on rate equations, a theoretical model of a fiber oscillator with a multimode gain fiber was built. We studied the effect of the rare earth doping profile in the core on the output characteristics of the multimode fiber oscillator. The results indicated that a pure fundamental mode can be obtained by partly doping the core of the large mode area （LMA） ytterbium doped fiber （YDF） in the fiber laser. Furthermore, a sole specific high-order mode can also be implemented by tailoring the rare earth doping profile according to the simulations. The mode coupling effect was also taken into account in the model. In spite of the mode coupling effect, the specific mode was able to dominate in the output of the fiber laser by utilizing the designed LMA YDF.     

Diode-pumped 1028 nm Ytterbium-doped fiber laser with near 90% slope efficiency

Highly efficient laser action from an Ytterbium-doped fiber (YDF) is demonstrated using a fiber Bragg grating (FBG) in conjunction with a 4% Fresnel reflection at room temperature. The YDF used is drawn from Yb₂O₃-doped preform, fabricated through deposition of porous layer of composition SiO₂-GeO₂ by the MCVD process in conjunction with a solution doping technique. The fabricated YDF has a core composition of 0.2 wt % of Yb₂O₃, 1.8 wt % of Al₂O₃ and 23 wt % of GeO₂ with a pump absorption of 9.0 dB/m. The fiber laser operates at wavelength of 1028 nm with a slope efficiency of 88% with respect to the launched 976 nm pump power using the YDF length of 7 m.     

1μm全光纤MOPA结构激光器输出特性研究

主振荡功率放大（main oscillation power amplification, MOPA）结构由于其光束质量良好和参数可调的优点,已成为高功率光纤激光器的主流设计之一。为了改善高功率掺镱光纤激光器（ytterbium-doped fiber laser, YDFL）的输出性能,提高系统的光-光转换效率,文中报道了一台基于915 nm泵浦激光器和双包层掺镱光纤（ytterbium-doped fiber, YDF）的MOPA结构全光纤高功率激光器。该高功率光纤激光器由电调制激光二极管（laser diode, LD）泵浦的种子激光器和掺镱光纤放大器（ytterbium-doped fiber amplifier, YDFA）组成。连续光（continuous wave, CW）工作模式下,激光种子源经过YDFA后,实现了中心波长为1 069.96 nm的激光输出,最大平均输出功率可达945.9 W,MOPA激光器整机的斜率效率高达74.12%,具有良好的稳健性。该研究方案对研制高功率MOPA光纤激光器具有参考意义。     

1028 nm single mode Ytterbium-doped fiber laser

An efficient Ytterbium-doped fiber laser (YDFL) operating at 1028 nm is demonstrated using a fiber Bragg grating (FBG). The Ytterbium-doped fiber (YDF) is drawn from Yb₂O₃-doped preform, fabricated through deposition of porous layer of composition SiO₂-GeO₂ by the MCVD process in conjunction with a solution doping technique. The fabricated YDF has a 0.1 mol % of Yb₂O₃ in the core, a Ytterbium ion lifetime of 1.1 ms, an absorption of 7.65 dB/m at 976 nm. The fiber laser has the maximum efficiency of 51% with pump power threshold of 19 mW using a FBG in conjunction with a Fresnel reflection to form a linear cavity resonator. The efficiency and threshold are better compared to the similar YDFL configuration using a commercial YDF.     

Tunable comb-filter using thermally expanded core fiber and ytterbium doped fiber and its application to multi-wavelength fiber laser

We constructed a novel tunable comb-filter by splicing a commercial Yb³⁺ doped fiber (YDF) between 2 thermally expanded core (TEC) fibers at their core-expanded ends. This structure forms an all-fiber Mach-Zehnder interferometer due to the interference between the core mode and the cladding modes of the YDF. The interference fringes shifts to the longer wavelength region as the YDF is pumped by a 980 nm laser diode (LD). We then demonstrated application of this newly proposed tunable comb-filter to a SOA-based ring laser and obtained multi-wavelength lasing. The lasing wavelengths can be also tuned by pumping the YDF in the proposed comb-filter.     

国产光纤实现直接抽运全光纤化3000 W级激光输出

基于国产光纤构建了直接抽运全光纤化主控振荡器功率放大器结构光纤激光器, 放大级分别采用武汉烽火锐光科技有限公司和中国电子科技集团公司第四十六研究所提供的国产20/400 μm掺镱双包层光纤作为增益光纤, 通过全国产化放大级实现了3050和3092 W的1080 nm激光输出. 放大级提取效率分别为67.3%和68.2%, 光-光效率分别为63.0%和63.9%. 据可查询资料, 这是公开报道的直接抽运全光纤激光输出的最高水平, 同时由于采用了国产光纤作为放大级增益光纤, 表明国产光纤具备了3 kW级光纤激光器输出能力. 通过国产光纤横截端面以及光纤熔接显微镜图像实验分析知, 光纤制造工艺的不足是导致国产光纤激光器效率低的主要原因. 继续改进光纤工艺, 提升抽运功率, 优化光纤长度, 有望实现更高功率的全国产化光纤激光器输出.     

Residual pump light as a probe of self-pulsing instability in an ytterbium-doped fiber laser

Self-pulsing instability in the ytterbium-doped fiber (YDF) laser is investigated with the pump-bypassed cavity configuration. The residual pump light acts as a probe of the intracavity dynamics, and the temporal behavior of the light shows correlations with the self-mode locking instability in the original cavity and the sustained self-pulsing instability in the modified cavity of the YDF laser. The results suggest that the interactions among stimulated emission, pump absorption and/or reabsorption could account for self-pulsing instability in the YDF laser. The pump-bypassed laser cavity configuration can be used to investigate the instabilities of various kinds of fiber lasers.     

热透镜控制激光光束质量技术研究

在端面抽运固体激光器中,就如何改善在高抽运功率时输出激光的光束质量,提出一种激光器的设计方法。在激光器谐振腔中放入多根掺杂浓度不同的激光介质,利用激光介质内部产生的热透镜控制抽运光和基模振荡光的空间分布,并且最大限度地使抽运光的分布区和基模振荡光分布区重叠,实现抽运光与基模振荡光在空间上高度匹配,进而提高抽运光能量的利用效率和振荡光的光束质量。实验表明,在不同抽运功率下,抽运光和基模振荡光在晶体内部的光斑的空间分布可通过热透镜加以控制。在端面抽运功率200 W附近时,实现了抽运光与基模振荡光较高程度匹配,光束质量因子M2由14.7改善为4.1。     

基于微纳光纤-单壁碳纳米管可饱和吸收体的被动调Q掺镱光纤激光器

为实现具有高脉冲能量的调Q脉冲激光输出,利用微纳光纤-单壁碳纳米管复合的方法制备可饱和吸收体,并对基于该类型可饱和吸收体器件的被动调Q掺镱光纤激光器进行研究。采用拉伸法将普通单模石英光纤拉制成微纳光纤,将其与单壁碳纳米管溶液复合,进一步制备成全光纤集成型器件。将该器件置于环形腔掺镱光纤激光器中,利用976 nm半导体激光器作为抽运源。当抽运功率为53 mW时,实现了调Q脉冲激光输出,激光中心波长为1 039 nm。进一步提升抽运功率至76 mW,可获得脉冲宽度为3.1μs、重复频率为25.5 kHz、单脉冲能量为941nJ的调Q脉冲激光输出。研究表明,利用微纳光纤制备的可饱和吸收体器件具有较高的损伤阈值,可用于实现高脉冲能量的激光输出。     

抽运调制条件下超窄线宽掺铒光纤环形激光器的跳模特性研究

搭建了基于光纤迈克耳孙干涉仪的跳模检测系统,对抽运调制条件下的超窄线宽掺铒光纤环形激光器的跳模特性进行了实验研究,测量了由抽运电流标定的表征跳模规律的跳模数据图。结果表明,随着抽运电流的不断增加,激光器先后经历模式稳定区、模式非稳区以及多纵模区三种状态;存在第二抽运阈值,当抽运强度超过这一阈值时激光器由单纵模跳变为非稳定的多纵模。掺铒光纤环形激光器的谐振腔因抽运热效应或外界扰动而变化时,会引发频率漂移与连续跳模现象。     

Mode-locked pulse generation from an all-FMF ring laser cavity

Experimental generation of stable mode-locked pulses and cylindrical vector beams(CVBs), from an all fewmode fiber(FMF) ring laser is first reported, to the best of our knowledge. In this laser, a section of few-mode erbium-doped fiber(FM-EDF) is used as the gain medium. The FM-EDF is pumped by 976 nm laser with LP11 mode, which is simultaneously converted and multiplexed through a homemade hybrid device, i.e., wavelength division multiplexing-mode selection coupler(WDM-MSC). All the components in our experiment are connected using FMF. The resulted CVB pulses have a spectral width of 0.33 nm with a repetition rate of 30.58 MHz under the pump power of 340 m W. Moreover, both azimuthally and radially polarized CVBs were achieved with a high purity of 95%. This mode-locked CVB fiber laser with an all FMF configuration opens the way to manipulate the transverse mode in mode-locked fiber lasers.     

Detecting lateral interfaces with focus‐engineered coherent anti‐Stokes Raman scattering microscopy

Focus‐engineered coherent anti‐Stokes Raman scattering (FE‐CARS) microscopy is used to highlight the lateral interfaces between chemically distinct media. Interface highlighting is achieved by using a HG10 mode for the Stokes laser beam and a HG00 mode for the pump laser beam in the forward detection scheme. The spectral and the orientation dependence of FE‐CARS are found to be in agreement with theoretical predictions. A brief discussion on the relevance of this technique for imaging third‐order nonlinear susceptibility interfaces in thin samples of biological or chemical importance is presented. Copyright © 2008 John Wiley & Sons, Ltd.     

Influences of ASE on the performances of Q-switched ytterbium-doped fiber lasers

The output characteristics of actively Q-switched ytterbium-doped fiber lasers (YDFL) are investigated in this paper. Our experimental results show that, the combined effect between the short switching time and the gain transient property of doped fiber causes the initial amplified spontaneous emission (ASE) power fluctuation, forming the multi-peak structure in the output pulse for either ring or linear cavity Q-switched YDFL. The pulse buildup time decreases with the rising of the pump. Moreover, since the broad-band ASE generated in the YDF is very high, it may saturate the doped fiber once the switch has been opened, making it difficult to achieve Q-switched laser oscillation for both fiber lasers. By using ASE filter to suppress the initial ASE, the gain supplied by the YDF can be greatly enhanced, which can not only decrease the threshold, but also greatly decrease the duration, and enhance the peak power of the Q-switched laser pulse as well. By using such an ASE filter, the Q-switched laser pulse with the peak power of 40.7 W and the duration of 30 ns has been achieved for the linear cavity YDFL pumped with 160 mW.     

高功率梯度掺杂增益光纤温度特性理论研究

在高功率光纤激光器中, 增益光纤的热效应是限制激光功率进一步提高的重要因素之一. 为了降低增益光纤的最高温度, 提出了一种通过改变增益光纤的掺杂浓度分布, 分散光纤激光的热效应, 从而提高激光输出功率的方法. 基于速率方程模型和热传导模型, 在光纤激光放大器输出功率大致相当的情况下, 对几种不同掺杂方式下增益光纤中的热分布和放大器的输出功率进行了数值模拟. 研究结果表明: 增益光纤的梯度掺杂可以优化光纤中的温度分布并提高光纤熔接点的稳定性; 同时兼具提高输出光束的光束质量、抑制光纤中非线性效应和模式不稳定的效果, 是提高光纤激光放大器输出功率切实可行的办法. 研究结果可以为高功率光纤激光器中增益光纤的设计提供一定的参考.     

光纤移频分布式布里渊光纤传感技术

提出了一种利用布里渊光纤环形腔移频技术实现分布式光纤布里渊传感的方法.该方法基于布里渊光时域分析法原理,将一束单纵模运转激光器输出的激光分为两束|一束光入射布里渊光纤环形腔中产生窄线宽的受激布里渊散射光作为斯托克斯光,另一束光经过低频相位调制后作为泵浦光|斯托克斯光和泵浦光分别相向入射进入传感光纤,通过测量布里渊谱得到光纤温度或应变.利用该方法可将十几GHz的微波频率转化为兆赫信号频率进行探测处理,仅需一台激光器,因此系统结构简单、成本低,还可减小激光器频率波动对测量准确度的影响.实验验证了该方法的可行性.     

Ultrafast fiber lasers for strong‐field physics experiments

The recent demonstration of rare‐earth‐doped fiber lasers with a continuous‐wave output power approaching the 10‐kW level with diffraction‐limited beam quality proves that fiber lasers constitute a scalable solid‐state laser concept in terms of average power. In order to generate high peak power pulses from a fiber several fundamental limitations have to be overcome. This can be achieved by novel experimental strategies and fiber designs that offer an enormous potential towards ultrafast laser systems combining high average powers (> kW) and high peak power (> GW). In this paper the challenges, achievements and perspectives of ultrashort pulse generation and amplification in fibers are reviewed. This kind of laser system will have a tremendous impact on strong‐field physics experiments, such as the generation of coherent light by high‐harmonic generation. So far, applications in the interesting EUV spectral range suffer from the very low photon count leading to nonrelevant integration times with highly sophisticated detection schemes. High repetition rate high average power fiber lasers can potentially solve this issue. First demonstrations of high repetition‐rate strong‐field physics experiments using novel fiber laser systems will be discussed.     

高斜率效率L波段宽带可调谐光纤环形腔激光器

利用环形腔结构在L波段获得了43nm(1567.1nm-1610.1nm）范围的宽带连续可调谐激光输出。由于同时采用了高浓度掺铒光纤和1480nm激光二极管（LD）抽运源，极大地降低了激光器的抽运阈值，提高了斜率效率和输出功率。在整个可调范围内，激光器的输出功率达10．9dBm-12.1dBm(95mW抽运），信噪比高于60dB，在1585nm的斜率效率为0．201。