反射光中Stokes成分对受激布里渊散射过程的影响

区别于传统的受激布里渊散射(SBS)发生器和放大器，提出了一种新型的SBS模型：自供种子光模型(self stokes seeding,SSS). 通过对抽运光波形函数的傅里叶变换得到了Stokes成分在抽运光中所占的比例，即Stokes能量比. 考虑SSS效应，数值求解了SSS耦合波方程组，得到了SBS反射率的时间演变形式，理论研究发现，当抽运光正入射到平板样品上时，反射光中的Stokes成分极大地促进了SBS起振过程，其结果相当于反向注入一定强度的种子光，而Stokes能量比的大小决定了SBS过程起振 关键词： 光学材料 受激布里渊散射 傅里叶分析 斯托克斯种子光     

Cooperative stimulated Brillouin and Rayleigh backscattering process in optical fiber

We observed an unusually narrow spectrum of Stokes field and Gaussian statistics of Stokes power for the stimulated Brillouin scattering (SBS) process in 300-m single-mode optical fiber with high Rayleigh losses. The measured characteristics of the Stokes radiation indicate that SBS lasing took place in the fiber. The effect is explained as the result of dynamic distributed feedback that is due to double Rayleigh scattering (RS) of the Stokes field. The results of numerical simulation of the cooperative SBS-RS process in fiber are in good agreement with experimental results.     

受激布里渊散射中Stokes光高频调制的抑制

受激布里渊散射中Ｓｔｏｋｅｓ光高频调制的抑制哈元清杨经国（四川大学物理系成都６１００６４）ＲｅｄｕｃｅｔｈｅＳｔｒｏｎｇＦｒｅｑｕｅｎｃｙＭｏｄｕｌａｔｉｏｎｏｆＳｔｏｋｅｓｉｎＳＢＳＨａＹｕａｎｑｉｎｇ，ＹａｎｇＪｉｎｇｇｕｏ（Ｄｅｐｔ．ｏｆＰｈｙ...     

受激布里渊散射相位共轭激光组束规律的研究

 提出了一种新的SBS激光组束的方法。此方法中，一束按时间分布的激光脉冲序列作为泵浦光从SBS放大池的一端入射，另一束Stokes频移种子光从SBS池的另一端入射，Stokes种子光在SBS池的相互作用区提取泵浦光能量。研究了组束效率和输出脉宽随脉冲串个数、间隔和泵浦功率密度等的变化规律。研究结果表明种子注入型泵浦脉冲串的受激布里渊散射相位共轭组束是一种高效的组束方法。     

横向受激布里渊散射的抑制

 从非线性光学的耦合波理论出发，结合流体力学的连续性方程，建立了光学元件中窄带泵浦的横向受激布里渊散射的二维理论模型，并在此基础上，利用数值模拟考察泵浦光带宽增加对受激散射过程的影响。研究表明:在一定的条件下，当泵浦光带宽略大于布里渊线宽时，受激散射过程的Stokes增益将显著降低；带宽越大，Stokes增益降低得越多；当带宽大于20GHz时，可以抑制横向受激布里渊散射带来的不良影响。另外，当带宽一定时，调制频率的改变也会影响受激散射过程，可以通过数值模拟确定最佳的调制频率。     

种子场对单池受激布里渊散射脉冲波形保真的影响

受激布里渊散射(SBS)产生池中引入种子光场，在种子场诱导下产生SBS，这不但可以降低SBS阈值，更可以获得最小的SBS脉冲形变，确保与抽运光波形基本一致，获得高波形保真.从理论和实验两方面研究了种子光强弱对脉冲波形保真的影响. 关键词： 受激布里渊散射 脉冲波形保真 注入种子     

光学透明材料中瞬态SBS过程的数值研究

建立了描述噪声起振和Stokes种子光辅助起振的SBS（受激布里渊散射）理论模型，利用变步长有限差分方法数值求解了一维瞬态后向SBS耦合波方程组，得到了抽运光和散射光光强以及介质密度变化量的时空分布；研究了Stokes激光场对SBS反射率以及发生阈值的影响，发现Stokes种子光的存在大大减短了SBS过程的起振时间，并且在抽运光脉冲宽度固定的情况下使SBS的发生阈值大幅度降低；最后，探讨了瞬态受激布里渊过程对光学材料破坏的可能性并对今后的工作进行了展望. 关键词： 光学透明材料 受激布里渊散射 斯托克斯种子光 反射率     

抽运光参数对受激布里渊散射的影响

受激布里渊散射（SBS）系统中,具有一定带宽的抽运激光中会含有一定比例的Stokes散射光成分，此Stokes散射光成分经SBS介质后表面反射后，将形成种子光与抽运光联合入射，构成自种子光式SBS放大器.通过数值求解此SBS放大器型耦合波方程组，探讨了抽运光脉冲中所含Stokes散射光成分的比例、抽运激光波长、抽运光能量大小、入射的聚焦高斯光脉冲脉宽、相互作用时间等激光参数对SBS特征参数（Stokes散射光脉冲波形、材料内部最大应力的时间演化及空间分布、脉宽压缩效果、能量提取效率及Stokes散射光的共轭保真度）的影响.同时发现，SBS过程中产生的超声应力不仅会对SBS介质前表面造成破坏，还可能对焦点附近造成破坏；调整各激光参数还会使焦点附近优于前表面先破坏.数值模拟中采用的抽运光是聚焦高斯光束. 关键词： 受激布里渊散射 斯托克斯散射光 冲击应力 能量反射率     

基于SBS效应激光波长对光学材料损伤的影响

从耦合波理论出发,采用纵向受激布里渊散射(SBS)模型,通过时域有限差分法数值求解了瞬态SBS耦合波方程组,得到了泵浦光、Stokes光强度及声波产生应力随时间的分布;研究了在三种常见波长激光(基频、倍频和三倍频)作用下SBS效应的发展过程及其对光学材料损伤过程的影响。结果表明:种子光作用主要体现在SBS起振阶段,一旦进入稳态阶段,Stokes光强及应力发展的最大值、稳态值依赖于泵浦光的大小;在相同脉冲宽度下,激光波长越短,SBS发生越早,发展越快,更易造成光学元件的力学损伤;三倍频激光产生最大应力为基频光产生最大应力的100倍,且相比于倍频激光,产生最大应力的时刻要提前15ns。     

Dynamics of Stimulated Brillouin Scattering in a Short and High-Finesse Fiber Fabry-Perot Resonator

We theoretically investigate the dynamics of stimulated Brillouin scattering (SBS) in a short fiber Fabry-Perot resonator with reflection mirrors. The analysis is based on the coherent six-wave model including an optical Kerr effect and the linear cavity detunings for the pump and created Stokes waves are taken into account in the formulation. The instabilities including periodic, quasi-periodic and chaotic oscillations can occur owing to the Kerr effect even if the fiber resonator is so short as to ensure a single longitudinal-mode operation. The threshold power for SBS and the boundary power between the stable and unstable regions are numerically calculated as a function of the amplitude reflectance of mirrors for different cavity detunings. The dynamics of SBS and these two critical powers depend on the amplitude reflectance and the cavity detuning. Although an increase in the mirror reflectance decreases the threshold power for SBS, it may limit the utility of SBS since the stable region is narrow and the output power levels of the pump and Stokes waves are low.     

Optical suppression of second-order stimulated Brillouin scattering in a simple focused beam cell

It has been investigated experimentally that the output energy and pulse-durational profile of first-order Stokes depend on the effective gain length due to the presence of the second-order SBS. The experimental results indicate that when the energy of an incident pump laser is strong enough and the effective gain length is relatively long, the self-accumulation of energy of first-order Stokes is enough to adequately reach a high peak power point to activate the second-order. The second-order SBS restrains the output energy of first-order to a great extent and plays an optical suppression role.     

Stimulated Brillouin scattering generation in ns pulsed double-cladding fiber amplifier

This paper proposes a study both in theory and experiment on the phenomenon of stimulated Brillouin scattering (SBS) in a double-cladding fiber amplifier. The distortion characteristic of the 200-ns is observed through a stationary coupled-wave SBS model including the second-order Stokes wave for double-cladding fiber amplifier. The first-order Stokes wave is amplified during backward propagation to such an intense peak power that it can generate second-order Stokes wave. The stochastic aspect of pulse distortion induced by SBS is also experimentally demonstrated in the single frequency 200 ns pulse amplifier with 12-m Yb³⁺ doped double-cladding fiber. The backward SBS pulse is observed when the pulse peak power is up to 3.3 W, and the pulse width of SBS is narrower than that of the input signal. In the meantime, to overcome the difficulty of the pulse spectrum measurement, a novel method is put forward to measure the SBS frequency shift using the F–P interferometer with free spectral rang of 30 G, showing a good agreement with the theoretical estimation. SBS is the main factor that limits the output pulse peak power in the amplification of the single-frequency pulse.     

单色光在损耗介质中激励的受激布里渊散射

研究了单色光在损耗介质中激励的受激布里渊散射，运用分布起伏噪声源模型描述了受激布里渊散射的产生过程，通过傅里叶变换，得到了输出斯托克斯光波的功率谱密度。     

Amplification effect on stimulated Brillouin scattering in the S-band forward G652 fiber Raman amplifier

The amplification effects on forward and backward stimulated Brillouin scattering (SBS) lines in the forward pumped S-band distributed G652 fiber Raman amplifier (FRA) have been studied. There is a pump threshold power of Stokes backward stimulated Brillouin scattering (B-SBS) line in the forward pumped G652 FRA, it is about 1 mW. The Stokes B-SBS lines are amplified by FRA and fiber Brillouin Brillouin gain. In experimental work, the saturation gain of the first order Stokes backward SBS line is about 58 dB and the saturation gain of 25-km G652 forward FRA is about 25 dB, so the gain of FBA is about 33 dB. The forward stimulated Brillouin scattering (F-SBS) is generated and amplified in S-band G652 FRA. The stimulated threshold powers of the forward first order Stokes SBS (SB1-), second order Stokes SBS (SB2-), and third order SBS (SB3-) in the forward pumped FRA are 2.3, 1.6, and 1.6 mW,respectively. In experimental work, the saturation gains of SB1-, SB2-, and SB3- are about 38, 62, and 60 dB, respectively. The saturation Raman gain of 25-km G652 forward FRA is about 8.8 dB, so the Brillouin gains of SB1-, SB2-, and SB3- are about 29.2, 53.2, and 51.2 dB, respectively. The forward and backward cascaded SBS lines have been observed.     

Statistical properties of stimulated Brillouin scattering in single-mode optical fibers above threshold

We performed numerical simulations to obtain statistical and spectral characteristics of stimulated Brillouin scattering (SBS) initiated by Gaussian noise in single-mode optical fibers. Recently published experimental spectra of SBS power [e.g., Phys. Rev. Lett. 85, 1879 (2000)] are explained completely by a one-dimensional SBS model. We give a clear physical insight into the problem and, for what is to our knowledge the first time, reveal how the probability function of Stokes power, the power-correlation function, and the SBS spectra evolve as key parameters of the model vary, leading to a modification of Stokes field statistics.     

Generation of multiorder Stokes and anti-Stokes lines in a Brillouin erbium-fiber laser with a Sagnac loop mirror

We have demonstrated a novel multiwavelength lasing scheme in which a Brillouin erbium-fiber laser with a Sagnac loop mirror and a metal-coated planar mirror were used. The Sagnac loop permitted the simultaneous presence of a stimulated Brillouin scattering (SBS) pump and Stokes lines within the loop and thus generated high-order Stokes and anti-Stokes waves through a four-wave mixing (FWM) process. A total of 34 lines of Stokes and anti-Stokes waves with 0.08-nm line spacing was generated through the SBS and FWM processes with 1.5-mW SBS pump power at 1561 nm and 80-mW erbium-doped-fiber pump power.     

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.     

Observation of inhomogeneous spectral broadening of stimulated brillouin scattering in an optical fiber

We report experimental results which show that the stimulated Brillouin scattering (SBS) spectrum in an optical fiber is inhomogeneous, exhibiting spectral broadening and hole burning under cw monochromatic laser excitation. This phenomenon arises from the waveguide interaction of the pump and Stokes signals and is a fundamental property of SBS in waveguiding systems due to their ability to confine a fan of radiation wave vector directions.     

Spectrum evolutions of spontaneous and pump-depleted stimulated Brillouin scatterings in liquid media

A theoretical model for calculating spontaneous and stimulated Brillouin scattering(SBS) spectra is described. An empirical formula for the Stokes output spectral linewidth, a function of spontaneous Brillouin linewidth and the exponential gain coefficient, is obtained by the calculated data fitting. The formula holds true for two cases involving pump undepletion and depletion. The lineshape change from spontaneous to highly pump-depleted SBS spectra is also investigated. The result shows that for the pump power below the SBS threshold, the Stokes output spectral lineshape evolves from Lorentzian to approximately Gaussian as the pump power increases. For the pump power near or beyond the threshold, the SBS spectrum is in the form of a steady Gaussian profile, and the spectral linewidth comes to a certain value about 7 times narrower than the spontaneous one. The theoretical results are experimentally demonstrated by using several common liquid media.     

Cavity enhanced stimulated Brillouin scattering in an optical chip for multiorder Stokes generation

We report the first demonstration of on-chip cascaded stimulated Brillouin scattering (SBS). Cascaded SBS is characterized in a 4 cm long chalcogenide (As?S?) rib waveguide where the end facet reflections provide a monolithic Fabry-Perot (FP) resonator. The presence of the FP cavity reduces the Brillouin gain threshold, which enables observation of cascaded SBS at reduced pump powers. We observe up to three orders of Stokes waves in the backscattered signal at a coupled peak power of 1.34 W. Anti-Stokes waves due to four-wave mixing between the pump and the Stokes wave were observed in the forward spectrum.