【摘要】：部分相干光在多模光纖中的傳輸對(duì)光通信的模式噪聲、天文光學(xué)成像以及散斑性質(zhì)的研究有重要的意義。在多模光纖中,輸出光的空間相干性除了與光源空間相干性有關(guān)外,還受限于時(shí)間相干性。因此,部分相干光在自由空間中和一般成像系統(tǒng)中的傳輸規(guī)律在多模光纖中不再適用。本文研究時(shí)間部分相干的單模激光經(jīng)階躍型多模光纖傳輸后空間相干性的變化。首先建立以模式間的互相干函數(shù)為元素的相干矩陣,對(duì)于階躍型多模光纖,在弱導(dǎo)、遠(yuǎn)離截止頻率和模式充分耦合的條件下,假設(shè)部分相干光與光纖耦合傳輸后出射端的各模式場(chǎng)具有相等的實(shí)數(shù)振幅,以及相鄰模式間具有相等的時(shí)延差。然后將相干矩陣對(duì)角化得到退相關(guān)的本征值譜。鑒于本征函數(shù)的求解困難導(dǎo)致實(shí)際上無(wú)法求輸出的復(fù)相干因子,本文提出對(duì)本征值譜做高斯近似和輸出的空間平移不變性假設(shè),基于本征函數(shù)的分析法得出輸出光的復(fù)相干因子以及散斑的襯比度。為了驗(yàn)證高斯近似理論的合理性,利用楊氏雙孔干涉實(shí)驗(yàn)研究了階躍型多模光纖輸出端的相干性隨空間變化的規(guī)律。此外,通過(guò)CCD分別測(cè)量了石英和塑料階躍型多模光纖輸出端面的散斑隨長(zhǎng)度的變化規(guī)律。實(shí)驗(yàn)結(jié)果基本驗(yàn)證了高斯近似理論的合理性。最后,根據(jù)散斑測(cè)量結(jié)果與近似理論分析的偏差,對(duì)該近似理論做了半唯象的修正。
[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 Therefore, the propagation law of partially coherent light in free space and in general imaging system is no longer applicable in multimode optical fiber.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.
【學(xué)位授予單位】：福建師范大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：TN253

【參考文獻(xiàn)】

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本文編號(hào)：2296557