【摘要】：自Allen在1992年指出渦旋光束具有軌道角動量(orbital angular momentum,OAM)以來,人們對渦旋光束在各個領域的應用產(chǎn)生了極大的興趣。由于渦旋光束所攜帶的OAM量子數(shù)可為任意整數(shù),因此理論上每一種渦旋光束可具有無窮多個OAM特征模。另外,渦旋光束各個OAM特征模之間的正交性有利于進行高速率的數(shù)據(jù)傳輸。近年來的研究表明,渦旋光束在大氣通信中具有巨大的應用潛力。然而,OAM在大氣湍流的影響下可能會發(fā)生嚴重的擴散,并進而在通信中產(chǎn)生嚴重的串擾。事實上,OAM擴散的產(chǎn)生降低了通信質量,并限制了通信距離。目前已經(jīng)找到了一些行之有效的方法以改善通信質量,如自適應光學等�？傮w來說,基于OAM的大氣光通信現(xiàn)在仍處于探索階段。本文主要做了以下幾方面的工作:1、研究了一種名叫環(huán)形光束(circular beam,CiB)的渦旋光束在大氣湍流中的傳播特性。研究結果表明當CiB的參數(shù)為某些特殊值時,CiB可具有會聚特性并進而使得OAM模在大氣湍流中呈現(xiàn)出自動的恢復效應,這意味著OAM擴散可發(fā)生逆轉。這一發(fā)現(xiàn)可提高初始OAM態(tài)的檢測概率,有利于改善通信質量。2、證實了二維疊加OAM態(tài)在大氣湍流中可以表現(xiàn)出協(xié)同效應。協(xié)同效應意味著二維疊加OAM態(tài)的檢測概率大于它的任一部分所表示的OAM本征態(tài)。另外通過分析發(fā)現(xiàn)協(xié)同效應主要來源于二維疊加OAM態(tài)的兩個OAM量子數(shù)互相變化的概率。當這一概率減小時,協(xié)同效應變?nèi)跎踔料А?、討論了大氣湍流中的旋轉相關函數(shù),并發(fā)現(xiàn)了具有任意波函數(shù)的OAM本征態(tài)在大氣湍流的弱浮動區(qū)域中傳播時其轉變?yōu)槠渌鸒AM本征態(tài)的概率都具有一個固定上限。初始OAM本征態(tài)轉變?yōu)橐粋�特定OAM本征態(tài)的概率上限僅取決于初始態(tài)的OAM量子數(shù)。4、研究了糾纏OAM光子對在大氣湍流中的特性。糾纏OAM光子對的制備來源于自發(fā)參量下轉換的方法。在這一方法中,泵浦光源用OAM模疊加而成。仿真結果表明,當接受態(tài)的波函數(shù)與泵浦光源的復振幅函數(shù)相一致時,檢測概率最大。另外對于糾纏情形,二維疊加OAM態(tài)的檢測概率略大于OAM本征態(tài)的檢測概率,并且這一差值在較強的湍流中更為明顯。
[Abstract]:Since Allen pointed out that vortex beams have orbital angular momentum (orbital angular momentum,OAM) in 1992, people have been interested in the applications of vortex beams in various fields. Since the OAM quantum number carried by a vortex beam can be an arbitrary integer, each vortex beam can theoretically have infinite OAM eigenmodes. In addition, the orthogonality of each OAM characteristic mode of vortex beam is favorable for high rate data transmission. Recent studies have shown that vortex beams have great application potential in atmospheric communications. However, under the influence of atmospheric turbulence, OAM may have serious diffusion and serious crosstalk in communication. In fact, the OAM diffusion reduces the communication quality and limits the communication distance. At present, some effective methods have been found to improve the communication quality, such as adaptive optics. In general, atmospheric optical communication based on OAM is still in the exploration stage. The main work of this paper is as follows: 1. The propagation characteristics of a vortex beam called annular beam (circular beam,CiB) in atmospheric turbulence are studied. The results show that when the parameters of CiB are some special values, CiB can have convergence characteristics and make the OAM model show an automatic recovery effect in atmospheric turbulence, which means that the OAM diffusion can be reversed. This discovery can improve the detection probability of the initial OAM state and improve the communication quality. 2. It is proved that the two-dimensional superposition OAM state can exhibit synergistic effect in atmospheric turbulence. The synergistic effect means that the detection probability of two-dimensional superposition OAM states is greater than the OAM eigenstates represented by any of its parts. In addition, it is found that the synergistic effect is mainly derived from the probability that two OAM quantum numbers of two dimensional superposition OAM states change each other. When the probability decreases, the synergistic effect becomes weak or even disappears. 3. The rotational correlation function in atmospheric turbulence is discussed. It is also found that the probability of transition to other OAM eigenstates of OAM eigenstates with arbitrary wave functions in the weakly floating region of atmospheric turbulence has a fixed upper limit. The upper limit of the probability of the transition of the initial OAM eigenstate to a specific OAM eigenstate depends only on the OAM quantum number of the initial state. The properties of entangled OAM photon pairs in atmospheric turbulence are studied. The preparation of entangled OAM photon pairs originates from the spontaneous parametric downconversion method. In this method, the pump source is superposed by OAM mode. The simulation results show that the detection probability is the highest when the wave function of the receiving state is consistent with the complex amplitude function of the pump light source. In addition, for entanglement case, the detection probability of two-dimensional superposition OAM state is slightly higher than that of OAM intrinsic state, and the difference is more obvious in strong turbulence.
【學位授予單位】：電子科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TN929.1

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相關期刊論文 前1條

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本文編號：2362686