Suppression of first order stimulated Raman scattering in erbium-doped fiber laser based LIDAR transmitters through induced bending loss

A model is presented for suppression of first-order stimulated Raman scattering (SRS) in pulsed Er-doped fiber amplifiers with wavelength-selective induced bending loss. The model estimates the effectiveness of SRS suppression through fiber coiling in a pulsed amplifier, considering both the single- and dual-clad fiber cases. The basic approach is to fit analytical expressions to the evolution of a quasi-CW signal in the amplifier. Then, assuming that SRS does not deplete the signal, exact analytical expressions for the propagation of the Stokes wave are determined, from which the SRS threshold is estimated. Finally, example calculations are presented, and the model is used to determine a fiber geometry for the suppression of SRS through fiber coiling.     

Distributed suppression of stimulated Raman scattering in an Yb-doped filter-fiber amplifier

Suppression of stimulated Raman scattering (SRS) is demonstrated in a cladding-pumped fiber amplifier. The Yb-doped amplifier fiber design incorporates a high-index ring that resonantly couples SRS wavelengths out of the gain material, thus filtering the gain. Modeling shows that fiber asymmetry plays an important role in the filtering spectrum.     

Numerical analysis of stimulated inelastic scatterings in ytterbium-doped double-clad fiber amplifier with multi-ns-duration and multi-hundred-kW peak-power output

We investigate the stimulated Brillouin scattering (SBS) and the stimulated Raman scattering (SRS) in an ytterbium-doped double-clad fiber amplifier that outputs optical pulses with multi-ns-duration and multi-hundred-kW peak-power. The ytterbium-doped double-clad fiber amplifier is simulated by a model which is composed of a set of propagation-rate equations. The simulated results show that SBS and SRS will deform the output signal pulse in both the time domain and the spectral domain, and degrade the performance of the ytterbium-doped double-clad fiber amplifier seriously. It is shown in our simulation that the troublesome SBS can be effectively suppressed by broadening the signal linewidth to a critical value of 0.07 nm in our calculation, and the effect of SRS can be suppressed using a large-mode-area fiber with proper length. The model and the simulated results are very useful for designing an ultra-high-power ytterbium-doped double-clad fiber amplifier.     

拉曼增益系数可分离光纤中的受激拉曼散射

给出了拉曼增益系数分离光纤的定义,在考虑了N个单色光之间的两两受激拉曼散射,得到了这种光纤中单向传输的N个不同的单色光之间的受激拉曼散射（SRS）稳态耦合波方程的解析解。它适用于各单色光功率任意大小、光频率分布不均匀时的一般情况。这一结果可应用于光纤通信系统、拉曼光纤放大器和拉曼光纤激光器的设计与分析。最后把解析解与数值解进行了比较,两者取得了很好的一致。     

密集波分复用系统中光纤喇曼放大器的分析方法

本文利用耦合波理论分析了密集波分复用系统中具有一定光谱宽度的光信号之间的SRS相互作用规律,给出了宽光谱光抽运的光纤喇曼放大器的分析方法.     

Utilization of stimulated Raman Scattering as secondary pump on hybrid remotely-pump l-band Raman/erbium-doped fiber amplifier

An L-band remotely-pumped erbium-doped fiber amplifier incorporating a secondary pumping scheme utilizing stimulated Raman Scattering (SRS) was demonstrated. 1423 nm Raman laser was employed to generate SRS which became the secondary pump source. The amplifier displayed excellent gain of up to 27.3 dB at 1570 nm for −30 dBm input. Noise figures were also kept to a minimum, with the highest figure measured at 11 dB which was influenced by imperfection of the C/L coupler utilized in this architecture. Overall transmission performance was measured as well and demonstrated an encouraging outcome with gain as high as 24 dB while the noise figure was maintained at about 11 dB. The L-band signal amplification was also contributed by the stimulated Raman scattering along the transmission fiber. The outcome of this study emphasized the feasibility of secondary pumping scheme using SRS in L-band gain enhancement.     

Optimization of a Raman/EDFA hybrid amplifier based on dual-order stimulated Raman scattering using a single-pump

Based on dual-order stimulated Raman scattering (SRS) of a single 1395 nm Raman fiber laser in 75 km single mode fiber and its corresponding dispersion compensation module, a hybrid Raman/Erbium doped fiber amplifier (EDFA) for long wavelength band (L-band) amplification is realized by inserting a segment of EDF within the span. By comparing the performance of gain and noise in four hybrid amplifiers with different span configurations, we find that the distribution of the secondary L-band amplification obtained from the EDF along the link has a great influence on the performance of the hybrid amplifier. Both gain and noise performance of hybrid amplifier can be improved significantly by optimizing the location of the EDF. Moreover, we can extend the flat gain bandwidth from L-band to central wavelength band (C-band) plus L-band by recycling the residual first-order SRS to pump a segment of EDF with proper length.     

抽运光谱宽度对喇曼光纤放大器的影响

采用受激喇曼散射（SRS）耦合波理论分析了抽运光谱宽度对喇曼光纤放大器的影响, 指出当采用宽光谱作抽运光时会降低抽运效率. 同时, 文中还给出了抽运光谱宽度、抽运光功率和抽运效率间的变化规律曲线, 得出当传输光纤的有效截面积越小、喇曼增益系数越大、抽运光的入纤功率和光谱线宽度越大时, 光谱抽运效率越小的结论.     

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.     

在同种光纤中实现RFA增益平坦化的方法

提出了一种新的光纤拉曼放大器设计方法:在同一种光纤内运用不同波长的泵浦光源达到前增益后补偿的目的,最终实现在放大器输出端信号光增益谱平坦化。通过对拉曼增益谱前后沿做线性化处理,化简稳态SRS耦合波方程的解析解,最终在输出端得到了一个固定的功率输出值。模拟结果表明:所设计的放大器具有增益平坦度好、增益高的优点,且设计方法简单。该方案为增益平坦化的拉曼光纤放大器设计提供了一种新的思路。     

Wide-band double-pass discrete Raman amplifier with reflection of signals and pumps

A wide-band(1530-1610 nm)and high efficient double-pass discrete Raman amplifier is reported.In this Raman amplifier,by using a one-end gilded fiber as the broadband reflector,signals and multi-pump are both reflected to propagate through the gain fiber for a second time.An increase in net gain of more than 150% has been achieved compared with that in the typical co-pumped Raman amplifier.The advantages of this proposed new configuration have been experimentally studied by comparing with the recently existing Raman amplifier configurations.     

Stimulated raman scattering in fiber optic systems

The effect of stimulated Raman scattering (SRS) in fiber optic communications is considered. On one hand, SRS limits the launch power in a multiple-channel communication system; while on the other hand, SRS can provide optical amplification in the 1.3-μm and 1.55-μm windows. In most of the previous work these issues have been treated separately by using different assumptions. A solution is usually obtained by solving differential equations. We present a numerical method that involves the simultaneous solution of integral equations describing SRS in optical fiber. The method is general enough to be applicable for wavelength division multiplexing (WDM), optic frequency division multiplexing (OFDM), and optical amplification. However, it is efficient and simple to program and uses just a few realistic assumptions. A WDM communication system with 10 optical channels in the 1.55-μm window is studied by using this method, The data rate is above 1 Gbps. The system parameters are such that the other nonlinear effects, such as stimulated Brillouin scattering and four-wave mixing, are less significant for the system. Launch power limitations imposed by SRS are investigated for IM / DD and coherent systems. The receiver dynamic range over the wavelengths of interest is an important factor in determining the launch power limitations. An optical amplifier in the 1.3-μm window is also analyzed. The two-pump technique is investigated. With pump power levels of about 500 mw 0-dB gain can be achieved for a 30-km repeaterless link. Finally, the calculated results agree with the experiments.     

High efficiency, high repetition rate, all-fiber picoseconds pulse MOPA source with 125?W output in 15?μm fiber core

A passive mode-locked fiber laser-delivered 13?ps pulse is saturatedly amplified with a four-stage amplifier chain. 125?W high power all-fiber picoseconds pulse laser is demonstrated in a 15-??m fiber core, and the optical-to-optical conversion efficiency of the main amplifier is up to 86.12?%. A home-made (6?+?1)?×?1 fiber combiner is used to couple the pump light and signal light into the gain double cladding fiber. In order to suppress the nonlinear effects in high-power picosecond fiber amplifiers, the repetition rate of the seed pulse is increased from 60?MHz to?~1?GHz; also the gain fibers are advisably selected. The amplified output spectrum is symmetrically broadened to several nanometers due to self-phase modulation (SPM). No stimulated Raman scattering (SRS), amplified spontaneous emission (ASE) and residual pump light are observed and the optical signal-to-noise ratio is more than 30?dB. The all-fiber picoseconds MOPA laser in this report can be easily performed with the conventional fiber handing equipments, and it has great potential to be applied as pump source in the fields of optical parametric oscillator, laser frequency-doubling and supercontinuum generation.     

大功率光纤放大器分段泵浦方式下的理论分析

利用数值算法计算了掺镱双包层光纤放大器分段泵浦方式下的稳态速率方程组,分析比较了双端泵浦和多段泵浦方式下的最佳光纤长度,最高温度和效率,并采用遗传算法对分布泵浦功率的大小和每段光纤长度同时进行了优化。结果表明,通过优化,大功率分段泵浦光纤放大器获得了较为平坦的温度分布,与双端泵浦相比,大大降低了最高工作温度,斜率效率略有下降。     

一种增益平坦的光子晶体拉曼光纤放大器

为解决传统拉曼放大器增益系数低和增益不平坦的问题,采用级联光子晶体光纤的设计方法设计了一种增益平坦的拉曼光纤放大器.采用受激拉曼散射效应的稳态分析理论,分析了光子晶体光纤的拉曼增益谱,建立了拉曼放大器的理论模型.通过解耦合方程,推导了实现增益平坦的约束条件,发现光纤长度和泵浦功率是影响拉曼光纤放大器增益平坦度的两个参数.仿真结果表明,在1 508～1 544 nm的带宽范围内,实现了一个增益高达21 dB,增益平坦度仅为0.14 dB的光子晶体拉曼光纤放大器,可在光纤通信系统应用中发挥重要作用.     

Simulation and experimental characterization of Raman/EDFA hybrid amplifier with enhanced performance

We present simulation and experimental characterization of a hybrid amplifier comprising of a Raman amplifier and an erbium doped fiber (EDF) amplifier, with enhanced performance. The incorporation of a pumped EDF section in a fiber Raman amplifier (FRA) employing a dispersion compensating fiber is demonstrated to provide superior performance than a sole FRA system. The hybrid amplifier is characterized in terms of single channel gain and noise figure, and the results of measurements are shown to be in close agreement with the simulated results. Polarization-dependent gain (PDG) and multi-channel measured and simulated gain characterization of the Raman/EDFA hybrid amplifier are also presented.     

高功率纳秒光脉冲在单模光纤中的受激喇曼散射及抑制研究

利用包含喇曼增益、抽运消耗、自相位调制、交叉相位调制和群速度色散效应的耦合非线性薛定谔方程组,对千瓦级高功率纳秒脉冲在单模光纤中的传输特性进行了模拟计算.分析了输入脉冲和斯托克斯脉冲的演化过程,研究了大模面积光纤对受激喇曼散射的抑制作用.研究结果表明,采用模面积为530 μm~2的光子晶体光纤作为惯性约束聚变脉冲整形系统的传输介质,能有效抑制受激拉曼散射,不但信号衰减较小,而且中心凹陷程度较低.     

孤子光脉冲的产生及其应用研究

利用非线性偏振旋转技术实现自起振被动锁模.在掺铒光纤环形腔激光器中产生了中心波长为1563.3 nm、重复频率为12.5 MHz、脉冲宽度为352.0 fs、3 dB光谱宽度为7.8 nm的孤子光脉冲.采用该孤子光脉冲作为抽运光源，经掺铒光纤放大器放大后，输入到101 m长的高非线性光子晶体光纤中，获得了20 dB带宽约为240 nm的超连续激光光谱.实验详细观测了光脉冲随抽运功率的变化及超连续激光光谱的形成过程，分析了其形成机理.研究表明：当抽运功率较低时，光谱加宽主要由高阶孤子的分裂引起；随着抽运功率的增加，高阶孤子分裂成基本孤子的数目逐渐增大，光谱进一步加宽；当抽运功率增加到受激拉曼散射的阈值时，受激拉曼散射成为光谱展宽的主要原因；抽运功率进一步增加时，受激拉曼散射、参量四波混频等非线性的共同作用将使光谱进一步加宽且变得光滑. 关键词： 孤子光纤激光器 超连续 光子晶体光纤     

LD泵浦光纤激光放大器实现13 kW高光束质量输出

光纤耦合半导体激光器（LD）泵浦的光纤激光放大器具有体积小、功质比高、稳定性好等优点,在工业加工和军事国防等诸多领域都有着广泛且重要的应用。然而,受限于器件制作工艺水平及光纤中的受激拉曼效应和模式不稳定效应,LD泵浦的光纤激光放大器难以同时实现高功率及高亮度激光输出。为实现更高功率、更高亮度的光纤激光输出,需要结合现有的器件工艺水平并同时实现对放大器中的受激拉曼散射效应和模式不稳定效应的有效抑制。报道了基于单位自研大模场增益光纤成功实现13 kW功率、高光束质量激光输出。激光器采用主振荡功率放大结构,放大级采用单后向981 nm泵浦自研大模场增益光纤,在总泵浦功率为15 kW时,输出功率达到12.94 kW,光束质量M2因子约为2.85。通过进一步优化器件性能及光纤模式控制,有望实现更高功率、更高亮度的光纤激光输出。     

大功率激光单模光纤远距离传输的注入光纤光功率限值分析

对于大功率激光单模光纤远距离传输, 采用传统的受激拉曼散射(SRS)阈值作为注入光纤激光功率值取值过大。本文对单模光纤远距离传输过程中泵浦光和拉曼斯托克斯光(Stokes)光功率随注入光纤激光功率的变化进行仿真与理论分析。根据光纤中SRS产生的机理, 提出以拉曼Stokes光在单模光纤中传输的光功率变化曲线曲率极大值点对应的注入激光功率为限值, 对注入单模光纤光功率限值随着光纤长度变化进行仿真, 通过曲线拟合得出注入单模光纤激光功率限值公式, 并搭建实验系统进行验证。结果表明, 提出的注入单模光纤激光功率限值适用于大功率激光远距离单模光纤传输。