基于1S0能级的Pr3+:ZBLAN光纤上转换紫外激光的数值模拟

在Pr3 ∶ZBLAN光纤中,运用粒子数速率方程理论,研究用586 nm和335 nm连续激光双光子激发4f组态最高能级1S0,以1S0和3F4为激光上下能级实现250 nm上转换紫外激光的动力学行为,得到阈值抽运功率、激光输出功率、斜率效率和最佳光纤长度等激光参数。结果表明,阈值抽运功率随光纤长度增加而增大,斜率效率随光纤长度增加而减小,光纤较短时,无法获得较高输出功率。掺杂浓度越大则阈值抽运功率越小,斜率效率越大。在选取的特定条件下,斜率效率最高可达16.7%。     

掺镱双包层光纤放大器的放大特性

从掺镱(Yb)光纤放大器的功率传输方程出发,利用有限差分法对小模场面积(SMA)和大模场面积(LMA)掺镱双包层光纤放大器的放大特性进行了分析比较.采用模场直径(MFD)6.5μm和20μm的双包层掺镱光纤作为放大器增益介质进行窄线宽连续信号的放大,在915 nm激光抽运下模拟计算了大、小模场面积输出功率随输入信号功率、抽运光功率和光纤长度的变化特性,特别是对于大模场面积光纤放大器,最优光纤长度的选择至关重要;讨论了模场直径不同时的最优抽运功率和光纤长度的选择,得出4 m光纤放大时的临界抽运功率为4 W,理论与实验结果基本一致.为实际应用中根据信号光、抽运光、增益和模式等要求而选择光纤长度和类型等优化设计提供了理论依据.     

Thermal effects in kilowatt fiber lasers

Thermal effects and their influences on kilowatt ytterbium-doped double-clad (YDDC) fiber lasers are studied through numerical modeling. Solutions to suppress the thermal effects in the YDDC fiber lasers under bidirectional end pump and distributed pump are presented and compared for the first time. It is shown that lower operating temperature and more uniform heat dissipation in fibers can be obtained by optimizing the arrangement of pump powers, pump absorption coefficients, and fiber lengths.     

单频大功率光纤放大器中抑制受激布里渊散射的理论分析

对单频大功率光纤放大器中的受激布里渊散射(SBS)抑制问题进行了分析和模拟。建立了双包层光纤放大器的含有受激布里渊散射效应的传输方程组,并考虑了温度差对受激布里渊增益系数的影响。通过数值求解方程组研究了前向、后向和双向抽运方式下,抽运功率、对流系数、光纤长度和斯托克斯频率偏移对受激布里渊散射增益的影响。在抽运功率、对流系数和光纤长度均相同的条件下,后向抽运方式的受激布里渊增益最小;对流系数或光纤长度的减少会降低受激布里渊增益。计算了总抽运功率为1kW,三段抽运方式下的受激布里渊增益,其结果远远大于增益阈值。因此,设计单频大功率光纤放大器宜采用后向抽运方式,尽量减小光纤外表面空气的对流速度以增加温度差,同时应该尽量缩短光纤长度。     

高功率远程泵浦传输系统的研究

针对远程泵浦传输系统高功率泵浦光传输受限问题,文章基于随机分布反馈光纤激光器的工作原理,创新性地提出了一种新型远程泵浦传输方案,通过高反射率的光纤布拉格光栅增强泵浦光的受激拉曼效应,输出目的泵浦光功率。对新型远程泵浦传输系统的传输性能进行了测试,测试结果表明,实验数据和理论计算数据一致;与传统远程泵浦传输系统相比,新型远程泵浦传输系统提高了泵浦的入纤光功率,延长了传输系统的传输距离。     

Heat dissipation in kilowatt fiber power amplifiers

The heat dissipation and output power characteristics of kilowatt ytterbium-doped double-clad (YDDC) fiber power amplifiers are investigated through numerical modeling. Solutions to facilitate heat dissipation and reduce operating temperature in YDDC fibers under bi-directional end pump and distributed pump are presented and compared. It is shown that the heat dissipation issue in kilowatt fiber power amplifiers can be effectively solved by optimizing the arrangement of pump powers, pump absorption coefficients, and fiber lengths.     

Theoretical and Experimental Analysis of Long-Period Fiber Gratings Made Directly Into Er-Doped Active Fibers

We present a rigorous theoretical and experimental analysis of signal propagation along a long-period fiber grating (LPFG) made in an Erbium-doped amplifying fiber (EDF). First, numerous effects that influence amplifying process in Erbium-doped fibers were considered. These are clustering of Er ions and subsequent upconversion and change of fiber refractive index due to the optical pumping. Subsequently, LPFG-assisted interaction between the amplified fiber core mode and a cladding mode is described combining rate equations that describe propagation through the EDF and coupled-mode equations that describe propagation through the LPFG. While this implementation is relatively straightforward for the signal and pump, it requires particular attention when dealing with spontaneous emission and amplified spontaneous emission (ASE) that are incoherent (described purely by amplitude), but have to diffract on the LPFG (that is amplitude and phase sensitive). This issue is carefully addressed here. As a result, we were able to rigorously describe the propagation of pump, signal, and ASE through the LPFG-amplifying diffractive structure considering effects such as pump depletion, shift of the coupling wavelength due to the pump power, and ASE formation along the structure. Forward pumping (pump copropagating with the signal) and backward pumping (pump counterpropagating to the signal) were both considered. The theoretical analysis was fully verified by carried-out experiments.      

Light propagation in the micro-size capillary injected by high temperature liquid

The high temperature liquid is injected into the micro-size capillary and its light propagation behavior is investigated. We focus on two different liquid pumping methods. The first method can pump the high temperature liquid tin into the micro-size capillary by using a high pressure difference system. After pumping, a single mode fiber (SMF) connected with the optical carrier based microwave interferometry (OCMI) system is used to measure different liquid tin levels in the micro-size capillary. The second method can pump the room temperature engine oil into the capillary by using a syringe pump. This method can avoid the air bubbles when the liquids are pumped into the capillary.     

Efficient gain-switched operation of a Tm-doped silica fiber laser

We present the results from experiments relating to a gain-switched Tm-doped silica fiber laser in which a gain-switched Nd:YAG laser is used to pump the ³H₅ energy level of the Tm³⁺ dopant ion. This fiber laser configuration is the first example to our knowledge of a moderate energy gain-switched fiber laser which is pumped with a low-repetition-rate high-energy pulsed laser. For a near-optimized cavity, the gain-switched fiber laser produces a maximum pulse energy of 1.46 mJ at a maximum linear slope efficiency of 20% and a total optical-to-optical efficiency (with respect to the launched energy) of 19%. At low pump energies, the slope efficiency is approximately 40%, however, saturation of the output pulse energy is observed with the increase in the launched pump energy. We also present results from a numerical model that simulates ³H ₅-band pumping and includes all of the known pump excited-state absorption (ESA) mechanisms and, in addition, four cross-relaxation mechanisms have also been included. The calculations establish that the pump ESA mechanism contributes only a small loss factor to the overall efficiency of the laser when the Tm-doped silica fiber laser is pumped at low pump energies, however, as the pump energy is increased, losses due to pump ESA limit the amount of output energy from the fiber laser. The loss mechanism is mainly attributed to pump ESA from the ³H₄ upper laser level to the combined ³F_2,3 energy level at low launched pump energies because of the large absorption cross section for this transition and the relatively long lifetime of the ³H₄ energy level. For harder pumping conditions, the majority of the excited state population resides in the ¹G₄ level, inhibiting in some laser configurations gain-switching of the fiber laser until cessation of the pump pulse itself     

高功率非对称泵浦耦合器理论研究

高功率非对称泵浦耦合器是高功率连续光纤激光器的关键无源光器件,它可以将多路泵浦光高效率地耦合进主光纤中,从而为光纤激光器提供所需的泵浦光功率,但已有双波导耦合理论并不能直接应用于该型耦合器的研究。为解决这一问题,在双波导定向耦合器的不完全耦合理论基础上,针对高功率泵浦耦合器非对称的特点,将其耦合系数和光功率方程组做了进一步推导,并进行了数值仿真,研究结果表明:两光纤中的光功率按照一定周期变化,当泵浦光纤的锥角在1~1.5之间时,可以获得97%以上的最佳耦合效率,且与其对应耦合长度的局部变化对耦合效率的影响较小。该研究结果对高功率非对称泵浦耦合器的设计及制作均具有指导意义。     

双向抽运拉曼光纤放大器抽运光功率分配对开关增益的影响

利用打靶法对单波长双向抽运拉曼光纤放大器的开关增益问题进行了数值仿真研究，结果表明，在小信号的情况下，只要抽运光的总功率不变，信号光的开关增益几乎与正反向抽运光功率的分配比例无关，此结果和小信号情况下的解析解结论一致。当信号光功率增大到对抽运光的消耗不能忽略时，其开关增益随着正向抽运光功率百分比的增大而略有增大。另外，也给出了几种不同输入信号入纤光功率、不同正反向抽运光功率分配情况下的信号光、正反向抽运光和总光功率沿光纤长度的分布。     

Analysis of Ultra-Broadband Amplified Spontaneous Emissions Generated by ${rm Cr}^{4+}{:}{rm YAG}$ Single and Glass-Clad Crystal Fibers

Numerical analysis and experimental verification of the ultra-broadband amplified spontaneous emissions (ASEs) generated by Cr⁴⁺:YAG crystal fibers are presented. Milliwatt ASE was obtained from a double-clad 25-mum-core fiber. Results of the experimental ASE power measurements and the composition analysis using electron probe micro-analyzer were used to determine the absorption, emission, and excited-state absorption cross sections of pump and signal of the crystal fibers. The numerical analysis showed that the ASE output power is improved by reducing the fiber core diameter down to several micrometers despite of the increased consumption in excited-state absorption of pump. A comparison of the cross sections between those in literature and this work indicates that the crystal fiber has good crystal and optical qualities using the laser heated pedestal growth method. The large pump absorption of the Cr⁴⁺:YAG crystal fiber limits its useful length. With such short fiber length, the ASE lights can not acquire enough gain. The ASE efficiency can be further improved by using bi-direction and cladding pump structure to increase the crystal fiber length and incorporating a high ASE reflector at the input end of the crystal fiber. The Cr⁴⁺:YAG crystal fiber has a potential for applying to ultra-broadband ASE light source in wavelength division multiplexing network.     

基于掺Er光纤放大器的可调谐微波光子滤波器

提出了一种基于掺Er光纤放大器(EDFA)的光纤环结构可调谐微波光子滤波器.在光纤环结构中引入掺Er光纤(EDF),通过增加泵浦功率提供增益来补偿器件损耗,从而增加了信号的有效采样数,大大改善了滤波器的性能.在泵浦功率为42.7 mW时,实现了通带3 dB带宽为0.15 MHz、Q值为100和抑制比为20 dB的微波光子滤波器.进一步通过在光纤环结构中引入可调光纤延迟线(TODL),实现了可调谐微波滤波器.     

基于交叉相位调制的孤子脉冲压缩效应研究

在负色散区 ,基本孤子在光纤中传输时其波形与脉宽保持不变。提出一种在负色散区利用交叉相位调制效应压缩基本孤子脉冲的新方法。采用分步傅里叶方法对非线性耦合方程进行了数值计算与模拟。研究了不同抽运功率、不同抽运脉冲啁啾参数以及不同脉宽对基本孤子脉冲压缩的影响。发现基本孤子脉冲不仅能够被压缩 ,而且光纤存在最佳压缩长度。在抽运功率一定的条件下 ,选取负啁啾的抽运脉冲 ,可获得更高压缩比的压缩光脉冲。另外 ,不同的脉冲宽度对孤子脉冲的压缩产生较大的影响 ,一般情况下 ,选用较窄的抽运脉冲易于产生较短的压缩光脉冲     

一种线形腔的多波长布里渊掺铒光纤激光器

布里渊掺铒光纤激光器(BEFL)是一种利用非线性效应——布里渊散射来实现多波长输出的激光器,波长间隔大约为0.088 nm(11 GHz).研究了一种多波长布里渊掺铒光纤激光器线形结构,通过引入反馈实现多波长输出.在布里渊泵浦功率为11 mW,980 nm泵浦功率为12 mW时获得了波长间隔为0.08 nm的34个波长的激光输出以及1 525～1 570 nm可调谐范围.并通过调节980 nm抽运光功率以及布里渊泵浦光波长,实现了可调谐的多波长输出.还研究了980 nm抽运光功率对产生的斯托克斯光波数的影响.     

Tunable microwave photonic filter based on a fiber ring and erbium-doped fiber amplifier

The tunable microwave photonic filter based on a fiber ring and erbium-doped fiber amplifier （EDFA） was proposed. By introducing a section of erbium-doped fiber （EDF） into the fiber ring, the loss of the signal can be compensated by the EDFA gain through adjusting the pump power. This can largely increase the number of the effective sampling taps, and then improve the performance of the microwave photonic filter notably. When the pump power was set to be 42.7 roW, a microwave bandpass filter with the 3-dB bandwidth of 0.15 MHz, the Q factor up to 100 and extinction ratio up to 20 dB was achieved. By employing a tunable optical delay line in the above fiber ring, a tunable microwave photonic filter has been realized through tuning the length of the optical delay line. The proposed tunable microwave photonic filter can fred great applications in microwave signal processing and ROF system.     

光纤光栅选频掺Yb3+光纤激光器

以波分复用器(WDM),光纤光栅和自行研制的掺Yb~(3+)单模光纤,采用新颖的全光纤连接方案,实现了1060nm窄线宽、线形腔激光器的成功运转。对不同长度掺镱光纤(YDF)所构成的激光器进行了实验研究,发现9m为最佳长度。入纤抽运阈值功率约为30mW,当入纤功率达到最大值42.8mW时,得到最大激光输出8.8mW,半宽<0.5nm,相对于入纤抽运功率的斜率效率为70.4％。     

Nondestructive measurement of length dependence of gain characteristics in fiber amplifiers

The authors describe a nondestructive method for determining the length dependence of the gain of a fiber amplifier. The method measures rapidly the length dependence of fiber-amplifier gain characteristics without resorting to cutback techniques. By extracting small amounts of signal power with a macrobend placed along the length of a fiber amplifier, the optical amplifier's gain, output power, pump efficiency, and optimal length can be determined without cutting the fiber. The macrobend was formed by bending the fiber over a rod. Transmitting only one modulated signal through the amplifier without the fiber being pumped makes it possible to measure the absorption of the fiber at any particular wavelength. By fitting to these curves, the absorption length of the pump, signal, or any other wavelength can easily be determined.<>     

Simultaneous operation of a Raman fiber amplifier and laser pumped by a dual-wavelength Nd/sup 3+/-doped fiber laser

This paper presents an experimental study on the dynamics of Raman fiber lasers that use highly GeO/sub 2/-doped fibers as an active medium and a dual-wavelength (1060 and 1090 nm) Nd/sup 3+/-doped fiber laser as a pump source. The 1090-nm pump wavelength is located within the SiO/sub 2/ Raman gain spectrum relating to the 1060-nm pump wavelength, and competition is observed between Raman amplification of the 1090-nm emission with the 1060-nm emission used as the pump source and Raman lasing, which is independent of the 1090-nm amplification and which is also uses the 1060-nm emission as the pump source. Several pump configurations have been demonstrated to generate specific Stokes emissions generated through Raman lasing or amplification. Changing the gain-to-loss ratio by introducing intracavity loss of Raman emissions or increasing the Raman fiber length within each configuration can force either Raman amplification or lasing to dominate. The maximum slope efficiency as a function of the launched pump power was /spl sim/55% with a total output power of 1.6 W produced. A red shift of both the pump and the Stokes wavelengths is experimentally observed when the launched diode pump power is scaled up.     

Laser diode-pumped holmium-doped fluorozirconate glass fiber laserin the green (λ~544-549 nm): power conversion efficiency, pumpacceptance bandwidth, and excited-state kinetics

The green (544-549 nm) Ho-doped fluorozirconate (ZBLAN) glass fiber laser, pumped in the red (λ~6;15 nm) by a high-power (~30 mW) InGaAlP laser diode or a ring dye-laser, has been characterized with regard to power conversion efficiency, fiber core-diameter and length, cavity output coupling, and pump acceptance bandwidth. Fibers doped with ~1200 ppm (by weight) of Ho and having core diameters of 1.7, 3, and 11 μm, and lengths ranging from 12.5 to 86 cm, have been studied in Fabry-Perot resonators having output couplings ranging from 1.545 to 96%. For a 1.7-μm core-diameter fiber, 21 cm in length, the threshold-launched pump power for the diode-pumped fiber laser is 1.9 and 3.5 mW for cavity output couplings of 1.5% and 24%, respectively. These values are the lowest for any upconversion-pumped fiber laser reported to date. Also, the noise and threshold-pumping power properties of the diode-pumped fiber laser are superior to those for its dye-laser-pumped counterpart. The highest laser slope efficiency (>22% with respect to launched pump power) was measured for a 3-μm core-diameter fiber and a cavity output coupling of 24%. The spectral interval over which the launched threshold pump power for this laser is <10 mW is almost 20 nm (637-656 nm). Studies of the fiber laser waveform as a function of pump power reveal competition for population between the ⁵S² and ⁵F₄ states and among the Stark sublevels of the ⁵F₄ manifold. Also, measurements of the output power on individual laser lines of the ⁵F₄, ⁵S₂→ ⁵I₈ (ground) transitions of Ho³⁺:ZBLAN as a function of pump power demonstrate the existence of a loss mechanism at the fiber laser wavelength, presumably due to absorption from ground or the ⁵I_y, ⁶S₂ or ⁵F₄ excited states of the ion