扭转环光纤传输特性研究和OAM模转换器设计

发布时间：2018-05-03 04:23

本文选题：环光纤 + 扭转光纤　；参考：《哈尔滨工业大学》2017年硕士论文

【摘要】：轨道角动量(Orbital angular momentum,OAM)是经典力学和量子力学的基本物理量,近来已经证明,光子也具有轨道角动量。光学上,它与射线束的空间相位分布有关,是具有螺旋相位的射线束的自然特性,这样的射线束又称为涡旋光。研究结果表明,OAM与光子的波长、极化等特性一样,是信息复用技术的一个新自由度。因而OAM光通信技术的研究近年来引起了世界各国科研工作者的广泛兴趣,取得了迅猛的发展。OAM光通信系统的组建包括OAM光束的产生、OAM信号的传输媒介和OAM的复用与解复用这三部分。本文的研究涉及前两部分,即OAM模转换器和OAM模在环光纤中的稳定传输。提出能稳定传输OAM模的光纤—扭转环光纤,该光纤所支持的正负涡旋之间有效折射率去简并,从而可用于稳定传输OAM模。现有涡旋光纤都是环光纤,OAM模本质上为矢量模(HEmn或EHmn)的奇偶型的叠加态,因此环光纤中OAM模正负涡旋简并是固有的问题。这使得涡旋光在传输中会因为微小的外部扰动而发生涡旋反转,造成OAM模传输不稳定。正负涡旋传输中功率交换的主要原因是它们之间相对小的有效折射率差。将环光纤施加扭转的方法可增大正负OAM模之间的有效折射率差,从而提高OAM模传输的稳定性。本文从理论和数值模拟上对弱导环光纤和高折射率对比度的环光纤进行了施加扭转的研究,在环光纤可承受的扭率极限内得到了理想的结果,所设计的扭转空气芯光纤可支持数个OAM模稳定传输上千米的距离。提出一种宽带宽的光纤OAM模转换器,应用于单模光纤通信网络与环光纤通信网络的连接。在光纤通信中,OAM模的传输介质是环光纤,而现有的通信网络使用的大多是单模光纤。针对环光纤与现有网络的连接问题,提出OAM模转换器的设想,即用单模光纤中基模来激发产生环光纤中OAM模。现有的光纤OAM模转换器,就我们目前所知,带宽都很窄,这实际上限制了频谱效率及通信容量的提高。但超材料实现的涡旋光生成具有带宽较宽的优点。因此,本文提出一种光纤端面超材料q-板,用来实现光纤中OAM模转换,并就工作带宽和生成效率,分别对金属等离子体超材料和电介质纳米鳍超材料OAM模转换器进行了理论和数值模拟上的研究。研究结果显示,金属超材料OAM模转换器的带宽可达800nm;电介质超材料OAM模转换器的带宽可达180nm,且转换效率和OAM模生成纯度都较高,分别63%和93%。
[Abstract]:Orbital angular momentum (Orbital angular momentum) is the basic physical quantity of classical mechanics and quantum mechanics. Recently, it has been proved that photons also have orbital angular momentum. Optically, it is related to the spatial phase distribution of a ray beam, which is the natural characteristic of a ray beam with helical phase, which is also called vortex light. The results show that OAM is a new degree of freedom in information reuse technology, which is similar to the wavelength and polarization of photons. Therefore, the research of OAM optical communication technology has attracted the extensive interest of researchers all over the world in recent years. The construction of OAM optical communication system includes the transmission medium of OAM beam and the multiplexing and demultiplexing of OAM. The first two parts, OAM mode converter and OAM mode, are studied in this paper. A torsional loop fiber which can stably transmit the OAM mode is proposed. The effective refractive index between the positive and negative vortices supported by the fiber is dedegenerate and can be used for stable transmission of the OAM mode. The existing vortex fiber is essentially an odd and even superposition state of vector mode HEmn or EHmnn, so the degeneracy of positive and negative vortices of OAM mode in annular fiber is an inherent problem. This results in vortex inversion in the propagation of vortex light due to small external disturbances, resulting in instability of OAM mode transmission. The main reason for power exchange in positive and negative vortex propagation is the relatively small effective refractive index difference between them. The effective refractive index difference between positive and negative OAM modes can be increased by torsion of ring fiber, thus the stability of OAM mode propagation can be improved. In this paper, torsion of weak guide ring fiber and high refractive index contrast ring fiber is studied theoretically and numerically. The ideal results are obtained within the limit of torsional rate of ring fiber. The torsional air core fiber can support several OAM modes to transmit thousands of meters. A wide band fiber OAM mode converter is proposed, which is applied to the connection between single mode optical fiber communication network and annular optical fiber communication network. In optical fiber communication, the transmission medium of OAM mode is ring fiber, while most of the existing communication networks use single mode fiber. Aiming at the connection between ring fiber and existing network, the idea of OAM mode converter is put forward, that is, the fundamental mode in single mode fiber is used to excite and generate OAM mode in ring fiber. As far as we know, the bandwidth of existing optical fiber OAM mode converters is very narrow, which actually limits the increase of spectrum efficiency and communication capacity. But the vortex light generated by metamaterials has the advantage of wide bandwidth. Therefore, this paper presents a kind of optical fiber end surface supermaterial q-board, which is used to realize OAM mode conversion in optical fiber, and in terms of working bandwidth and generation efficiency, The theoretical and numerical simulation of metal plasma supermaterial and dielectric nano-fin supermaterial OAM mode converter are presented. The results show that the bandwidth of metal supermaterial OAM mode converter can reach 800 nm, and that of dielectric supermaterial OAM mode converter can reach 180 nm, and the conversion efficiency and the purity of OAM mode generation are higher, 63% and 93%, respectively.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.11;TN253

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