A 168-W high-power single-frequency amplifier in an all-fiber configuration

We present a high-power, single-frequency, narrow linewidth fiber amplifier based on master oscillator power amplification chains in an all-fiber configuration. The effect of the delivery fiber on the maximum output power is studied. A home-made 1064-nm seed laser with a 20-kHz linewidth is boosted to 129 W, and limited by stimulated Brillouin scattering (SBS) when the delivery fiber is 1.2 m long. By shortening the delivery fiber length to 0.7 m, the SBS threshold is increased efficiently and the maximum output power rises to 168 W with an 82.9% power conversion efficiency. The experimental results indicate that the output power can be further raised by shortening the delivery fiber length and increasing the pump power.     

窄线宽纳秒脉冲光纤拉曼放大器的理论模型和数值分析

窄线宽纳秒脉冲光纤拉曼放大器在非线性频率变换、遥感探测和量子信息等领域有广泛的应用前景.综合考虑受激拉曼散射(stimulated Raman scattering,SRS)、受激布里渊散射(stimulated Brillouin scattering,SBS)、自相位调制(self-phase modulation)和交叉相位调制(cross-phase modulation)等非线性效应,建立了窄线宽纳秒脉冲光纤拉曼放大器的非线性动力学模型.仿真分析了放大器中脉冲激光的时频演化特性,对比研究了抽运脉冲宽度、光纤长度和信号光功率等因素对放大器性能的影响.研究发现,上述因素会影响放大器的SRS阈值、SBS阈值、输出激光线宽、激光转换效率等.例如,当脉冲宽度为800 ns时,SBS随着抽运功率的增加而发生,限制了激光功率的提升;减短抽运脉宽可以抑制SBS,但是输出激光的线宽易于展宽到数百MHz以上;增加光纤长度可以获得更低的SRS阈值和更高的转换效率,但是SBS效应和光谱展宽程度也随之增强.系统搭建中需要平衡各非线性效应,选择合适的系统参数.研究内容可以为窄线宽纳秒脉冲光纤拉曼放大器的设计搭建提供参考.     

Stimulated Brillouin Scattering Enhancement Factor Improvement in a 11.6-GHz-Linewidth 1.5-kW Yb-Doped Fiber Amplifier

The stimulated Brillouin scattering(SBS) threshold enhancement factor in a pure white noise linewidth broadening Yb-doped fiber amplifier(YDFA) with a short large mode area fiber is theoretically and experimentally studied.We demonstrate a 1064.08 nm,11.6 GHz linewidth,1.5kW output power YDFA with an SBS threshold enhancement of ~57(26 W SBS threshold with single frequency seed).The output beam is near-diffraction limited with a beam quality factor of M~2 = 1.15 and a slope efficiency of up to 87%.No SBS or stimulated Raman scattering effects are observed in the whole power range.Further power scaling is limited by the available pump power in our system.     

Numerical analysis of stimulated Brillouin scattering in high-power double-clad fiber lasers

A theoretical analysis of stimulated Brillouin scattering (SBS) in linear cavity Yb³⁺-doped double-clad fiber lasers is presented by solving the steady-state rate equations with the SBS. The effects of cavity length, fiber core diameter, input mirror reflectivity at Stokes wavelength, Yb³⁺ concentration and laser linewidth on the SBS are discussed. Numerical results show that the SBS threshold power can be improved by shortening the cavity length, using large mode area fiber, reducing the input mirror reflectivity at Stokes wavelength, lowering the Yb³⁺ concentration and broadening the laser linewidth, and the influence of the laser linewidth on the SBS threshold power is more noticeable than other system parameters.     

1.06kW 13GHz线宽全光纤激光器

分析了高功率光纤激光器中受激布里渊散射(SBS)效应的抑制方法。研究表明,利用宽带噪声源高速相位调制展宽光谱的方法对于抑制SBS十分有效,可实现kW级用于光谱组束的数10GHz高功率光纤激光子束。通过理论计算线宽与SBS阈值的关系,并分析噪声相位调制各参数对SBS阈值提升的影响,优化了光纤激光器设计参数。通过宽带噪声高速相位调制的方法,展宽单频种子源线宽至13GHz,通过两级预放大至10 W后,使用20/400μm掺Yb光纤最终实现了中心波长1064nm、线宽13GHz、最高功率1.06kW的激光输出,光束质量M21.2,光-光转换效率86%,实验过程未观测到模式不稳定性现象。进一步扩宽噪声源频带,加大调制深度,有望实现更高功率的窄线宽光纤激光输出。     

百瓦级全光纤结构单频掺铥主振荡功率放大器

报道了平均功率超过百瓦的单频掺铥全光纤结构主振荡功率放大器。使用线宽小于100kHz、中心波长为1.97μm的单频种子源进行级联放大,主放大器的斜率效率为50%。监测放大器的回光功率和光谱,没有发现受激布里渊散射以及其他非线性效应。通过增加泵浦功率,可以获得更高功率的掺铥单频放大输出。     

122-W high-power single-frequency MOPA fiber laser in all-fiber format

We demonstrate a high-power single-frequency master oscillator power amplifier (MOPA) fiber laser.The central wavelength of the single-frequency fiber laser seed is 1 063.8 nm,with a linewidth narrower than 20 kHz and output power of 120 mW.By using two-stage amplification,a single-frequency fiber laser with an output power of 122 W is obtained,and the optical-optical conversion efficiency is 72%.No significant amplified spontaneous emission (ASE) or stimulated Brillouin scattering (SBS) is observed.The output power can be further increased by launching more pump power.     

18 W single-stage single-frequency acoustically tailored Raman fiber amplifier

A single-mode polarization-maintaining fiber doped to increase the Raman gain while suppressing stimulated Brillouin scattering (SBS) was utilized in a single-stage counter-pumped Raman fiber amplifier. The SBS suppression was achieved through the acoustic tailoring of the core. A pump probe experiment was conducted to characterize the Brillouin gain and indicated the existence of multiple Brillouin peaks. When the amplifier was seeded with approximately 15 mW of 1178 nm light, 11.5 W of cw output power was obtained with a linewidth ≤2 MHz. The application of a thermal gradient to further mitigate the SBS process increased the output power to 18 W, thus providing a net amplifier gain >30 dB.     

窄线宽1064 nm光纤激光泵浦高效率中红外3.8μm MgO:PPLN光参量振荡器

采用放大1064?nm掺镱光纤激光器作为泵浦源,实现了中红外3.8?μm?MgO:PPLN光参量振荡(OPO)激光输出.在泵浦源中,采用分布式反馈激光器(DFB)作为种子源来实现光纤激光窄线宽的调制,实现线宽2.5?nm到0.1?nm的压缩,最大平均输出功率可达40?W.进一步对不同泵浦线宽条件下中红外3.8?μm?M...     

All-fiber clad-pumped Tm3+-doped fiber amplifier using high power fiber combiner

The diode laser (LD) clad-pumped 1947.6 nm continuous wave (CW) Tm³⁺-doped fiber amplifier is reported using the master oscillation power amplifier (MOPA) method. The injected seed laser is provided by an all-fiber LD-clad-pumped Tm³⁺-doped single-mode fiber laser, which has a nearly 2.4 W maximal output power and 0.1 nm ultra-narrow linewidth based on the intracore reflection FBG. Using the 25/400 μm double-clad LMA Tm³⁺-doped fiber as the gain fiber, the output maximal output power is 30.6 W from the fiber amplifier, with a slope efficiency of 39.1% respected to the LD total output power. A high power multi-mode fiber combiner is used to couple high power LD light into the gain fiber. The output wavelength is also located at 1947.6 nm, with the slightly expanded laser linewidth of 0.2 nm.     

基于简单MOPA结构实现3.08 kW全光纤窄线宽线偏振激光输出

基于简单的主振荡功率放大结构,演示了一种高功率窄线宽线性偏振全光纤激光器,其最大输出功率为3.08 kW,3 dB线宽为0.2 nm。在整个功率缩放过程中,偏振消光比约为94%,光束质量M 2约为1.4。这是国内外首次实现3 kW全保偏光纤激光输出,与基于相位调制的窄线宽激光器相比,该激光器可实现近似的线宽,同时具有受激布里渊散射阈值高、系统结构简单、成本低等特点。     

窄线宽脉冲光纤激光的自相位调制预补偿研究

自相位调制(SPM)效应会展宽窄线宽脉冲光纤激光的光谱宽度,降低其相干性.通过相位调制对SPM引起的非线性相移进行预补偿,能够使脉冲激光在光纤中进行放大和传输后保持种子激光的光谱特性.基于三波耦合方程开展数值仿真,研究了在对SPM进行"欠补偿","完全补偿"和"过补偿"的情况下,SPM预补偿对受激布里渊散射阈值和激光光谱特性的影响.开展了SPM预补偿实验研究,将脉冲激光的光谱宽度从1.4 GHz压缩到120 MHz.研究内容可以为窄线宽脉冲光纤激光系统的设计搭建提供参考.     

基于光纤中SBS相位共轭的自调Q光纤激光器

分析了利用光纤中的受激布里渊散射(stimulated Brillouin scattering,SBS)相位共轭效应进行激光腔内调Q,产生ns量级脉冲激光的原理,并对利用该效应产生的激光脉冲波形和脉冲形成过程进行了数值模拟,得到的脉冲波形与SBS相位共轭反射率随时间变化曲线基本一致,表明利用光纤中的SBS相位共轭作用调Q具有可行性.据此,对采用单模光纤(single-mode fiber,SMF)作为SBS池的Er³⁺掺杂调Q光纤激光器进行实验研究.当单模光纤长度为1.5 m时,在45 mW的光抽运功率下得到脉宽约2.6ns,脉冲周期58.23ns,平均功率7.35mW的激光脉冲.进一步的研究表明:激光器中相位共轭镜的形成与SBS介质长度有关,SBS介质过长,斯托克斯线之间无固定的相位关系,不能形成相干叠加,SBS相位共轭腔不能形成;SBS介质过短,腔内正交偏振模光子寿命的改变使脉冲出现双峰现象.脉冲形成后其属性只与SBS动态属性有关.     

Output Characteristics of High-Power Continuous Wave Raman Fiber Laser at 1239 nm Using Phosphosilicate Fiber

A high-power singlemode Raman fiber laser (RFL) with maximum output power of 4.11 W and maximum power conversion efficiency of 47.40% at 1239 nm is realized using continuous wave 8.4 W Yb-doped double-clad fiber laser as a pump, 700 m phosphosilicate fiber, and a Raman cavity formed by a pair of fiber Bragg grating mirrors at 1239 nm. The output characteristics of the RFL at 1239 nm for different fiber lengths and output mirror reflectance are reported. Theoretical simulation is done to numerically optimize for fiber length and output coupler reflectivity to obtain maximum first Stokes power.     

22 GHz窄线宽全光纤激光器实现2.62 kW近衍射极限输出

基于大模场面积掺镱光纤搭建了全光纤1064 nm高功率窄线宽光纤激光主振荡功率放大系统,实现了2625 W的最高功率输出,斜率效率76%。最高输出功率时,光束质量为Mx2=1.273,My2=1.255,3 dB光谱宽度为21.7 GHz,这是目前全光纤激光器在该光谱线宽下实现的最高输出功率。     

20 W passively cooled single-mode all-fiber laser at 2.8 μm

A maximum output power of 20.6 W at 2.825 μm from an erbium-doped all-fiber laser is reported, which we believe is the highest output power for this laser transition in single-mode operation. The slope efficiency of the passively cooled laser was up to 35.4% with respect to the absorbed pump power. Accounting for an estimated round-trip intracavity loss of 1.3 dB, we calculated a theoretical conversion efficiency of 39.5%, which is 15% higher than the Stokes efficiency of 34.3%. We believe this is the first experimental confirmation of the predicted pump energy recycling for this fiber laser. The narrow laser linewidth varied from 0.09 to 0.16 nm from low to maximum output power.     

相位调制信号对窄线宽光纤放大器线宽特性和受激布里渊散射阈值的影响

高功率窄线宽光纤放大器的输出功率主要受限于受激布里渊散射(SBS)效应,通过相位调制进行线宽展宽可以有效抑制SBS效应.基于窄线宽光纤放大器中的SBS动力学模型,研究了正弦信号、白噪声信号和伪随机编码信号(PRBS)对窄线宽光纤放大器光谱特性与SBS阈值的影响.研究发现,采用不同信号进行相位调制时,调制频率和调制深度等参数对调制后激光光谱的谱线间隔、谱线数目与光谱平整度的影响存在较大差异,进而影响放大器的线宽特性和SBS阈值.通过对比分析,给出了调制信号的类型选择和参数优化原则,能够为窄线宽光纤放大器的相位调制系统设计提供参考.     

Narrow linewidth CW amplification of a Tm-doped double-clad fiber MOPA system

A Tm-doped double-clad fiber MOPA system is built. Amplification characteristics of a Tm-doped double-clad narrow linewidth fiber master oscillator (MO) are investigated both experimentally and numerically. Linewidth of the fiber MO is only 112 pm at 3 W output. The output and efficiency of the MOPA system increase with the injected seed power. When the seed power is increased to 2 W, a maximum output of 10.5 W is obtained with a slope efficiency of 41.5%. Spectral center of the output lies at 1996.7 nm with the linewidth no bigger than 120 pm throughout the experiment.     

Output Characteristics of High-Power Continuous Wave Raman Fiber Laser at 1484 nm Using Phosphosilicate Fiber

A continuous wave (CW) high-power Raman fiber laser (RFL) with maximum output power of 2.24 W and slope efficiency of 32.8% at 1484 nm is obtained using a CW 8.4 W/ 1064 nm Yb-doped double-clad fiber laser as a pump, 700 m phosphosilicate fiber, and cascaded cavities with two pairs of fiber Bragg grating mirrors for the first and the second Stokes orders. Theoretical simulation of the RFL using a very efficient and rapidly converging collocation method is done to understand and optimize the fiber length to obtain maximum second Stokes power. RFL performance for the 300, 700 and 1150 m phosphosilicate fiber lengths was experimentally investigated by observing maximum output power, slope efficiency, threshold power, and full-width at half maximum at the second Stokes wavelength.     

High-power and wavelength-tunable operation of an Er,Yb fiber laser using a volume Bragg grating

Efficient high-power operation of double-clad Er,Yb-doped fiber lasers with fixed-wavelength and wavelength-tunable resonator configurations using volume Bragg gratings for wavelength selection are reported. The fixed-wavelength laser yielded a maximum output power of 103 W at 1552.6 nm with a linewidth of ~0.4 nm (FWHM) for a launched pump power of 290 W at 976 nm. The wavelength-tunable laser could be tuned from 1528 to 1550 nm with a linewidth of 0.2 nm (FWHM) and with output power in the range 30-38 W for a launched pump power of 120 W. The prospects for further improvement in performance are considered.