受限于时间相干的单模激光在阶跃多模光纤的传输理论及其验证
发布时间：2018-10-26 18:14
【摘要】：部分相干光在多模光纤中的传输对光通信的模式噪声、天文光学成像以及散斑性质的研究有重要的意义。在多模光纤中,输出光的空间相干性除了与光源空间相干性有关外,还受限于时间相干性。因此,部分相干光在自由空间中和一般成像系统中的传输规律在多模光纤中不再适用。本文研究时间部分相干的单模激光经阶跃型多模光纤传输后空间相干性的变化。首先建立以模式间的互相干函数为元素的相干矩阵,对于阶跃型多模光纤,在弱导、远离截止频率和模式充分耦合的条件下,假设部分相干光与光纤耦合传输后出射端的各模式场具有相等的实数振幅,以及相邻模式间具有相等的时延差。然后将相干矩阵对角化得到退相关的本征值谱。鉴于本征函数的求解困难导致实际上无法求输出的复相干因子,本文提出对本征值谱做高斯近似和输出的空间平移不变性假设,基于本征函数的分析法得出输出光的复相干因子以及散斑的衬比度。为了验证高斯近似理论的合理性,利用杨氏双孔干涉实验研究了阶跃型多模光纤输出端的相干性随空间变化的规律。此外,通过CCD分别测量了石英和塑料阶跃型多模光纤输出端面的散斑随长度的变化规律。实验结果基本验证了高斯近似理论的合理性。最后,根据散斑测量结果与近似理论分析的偏差,对该近似理论做了半唯象的修正。
[Abstract]:The transmission of partially coherent light in multimode optical fiber is of great significance to the study of mode noise, astronomical optical imaging and speckle properties of optical communication. In multimode optical fiber, the spatial coherence of output light is not only related to the spatial coherence of light source, but also limited by time coherence. Therefore, the propagation law of partially coherent light in free space and in general imaging system is no longer applicable in multimode optical fiber. The spatial coherence of time partially coherent single mode laser propagating through step multimode fiber is studied in this paper. First of all, a coherent matrix based on the interaction function between modes is established. For a step multimode fiber, under the condition of weak conductance, far from cutoff frequency and full coupling of modes, It is assumed that the mode fields at the emitter end have equal real amplitude and the delay difference between adjacent modes is equal after the coupling of partially coherent light and optical fiber. Then the diagonalization of the coherent matrix is used to obtain the eigenvalue spectrum of declination. In view of the difficulty in solving the eigenfunction and the difficulty in finding the complex coherence factor of the output in practice, the assumption of Gao Si approximation and spatial translation invariance for the eigenvalue spectrum is proposed in this paper. The complex coherence factor of the output light and the contrast degree of speckle are obtained based on the analysis of eigenfunction. In order to verify the rationality of Gao Si's approximation theory, the coherence of the output end of step multimode fiber is studied by using Young's double-hole interference experiment. In addition, the variation of speckle with length on the output end of quartz and plastic step multimode fiber was measured by CCD. The experimental results basically verify the rationality of Gao Si's approximation theory. Finally, according to the deviation between the speckle measurement results and the analysis of the approximate theory, the semi-phenomenological correction of the approximate theory is made.
【学位授予单位】：福建师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN253
[Abstract]:The transmission of partially coherent light in multimode optical fiber is of great significance to the study of mode noise, astronomical optical imaging and speckle properties of optical communication. In multimode optical fiber, the spatial coherence of output light is not only related to the spatial coherence of light source, but also limited by time coherence. Therefore, the propagation law of partially coherent light in free space and in general imaging system is no longer applicable in multimode optical fiber. The spatial coherence of time partially coherent single mode laser propagating through step multimode fiber is studied in this paper. First of all, a coherent matrix based on the interaction function between modes is established. For a step multimode fiber, under the condition of weak conductance, far from cutoff frequency and full coupling of modes, It is assumed that the mode fields at the emitter end have equal real amplitude and the delay difference between adjacent modes is equal after the coupling of partially coherent light and optical fiber. Then the diagonalization of the coherent matrix is used to obtain the eigenvalue spectrum of declination. In view of the difficulty in solving the eigenfunction and the difficulty in finding the complex coherence factor of the output in practice, the assumption of Gao Si approximation and spatial translation invariance for the eigenvalue spectrum is proposed in this paper. The complex coherence factor of the output light and the contrast degree of speckle are obtained based on the analysis of eigenfunction. In order to verify the rationality of Gao Si's approximation theory, the coherence of the output end of step multimode fiber is studied by using Young's double-hole interference experiment. In addition, the variation of speckle with length on the output end of quartz and plastic step multimode fiber was measured by CCD. The experimental results basically verify the rationality of Gao Si's approximation theory. Finally, according to the deviation between the speckle measurement results and the analysis of the approximate theory, the semi-phenomenological correction of the approximate theory is made.
【学位授予单位】：福建师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN253
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