Spontaneous Brillouin Scattering Spectrum and Coherent Brillouin Gain in Optical Fibers
Spontaneous Brillouin Scattering Spectrum and Coherent Brillouin Gain in Optical Fibers
复制标题
光纤中的自发布里渊散射谱和相干布里渊增益
作者：
V. Laude;J. Beugnot
布里渊光散射描述了光波通过声学声子的衍射，该声学声子源自透明体内的随机热波动，或者通过由换能器产生的相干声波或来自两个频率失谐的光波的干涉。在光纤的实验中，通常发现自发布里渊频谱具有与相干布里渊增益相同的频率依赖性。我们研究的起源，这种相似性之间的明显不同的物理情况。我们具体解决的弹性动力学方程，给出体内的位移，随机朗之万激发下，并响应于相干光的力量。需要强调的是，相位匹配负责激励的时间和空间频域滤波，在任何一种情况下都会导致仅由弹性损耗确定的洛伦兹频率响应的激励。
Brillouin light scattering describes the diffraction of light waves by acoustic phonons, originating from random thermal fluctuations inside a transparent body, or by coherent acoustic waves, generated by a transducer or from the interference of two frequency-detuned optical waves. In experiments with optical fibers, it is generally found that the spontaneous Brillouin spectrum has the same frequency dependence as the coherent Brillouin gain. We examine the origin of this similarity between apparently different physical situations. We specifically solve the elastodynamic equation, giving displacements inside the body, under a stochastic Langevin excitation and in response to a coherent optical force. It is emphasized that phase matching is responsible for temporal and spatial frequency-domain filtering of the excitation, leading in either case to the excitation of a Lorentzian frequency response solely determined by elastic loss.