石墨烯离散波导阵列成像与光束调控特性

发布时间：2018-10-16 21:44

【摘要】：超构材料通过亚波长微结构的设计可以实现等效电磁参数调控,从而实现超构材料与光波作用方式的调控。光波在其中传输时,会出现许多在自然材料中所没有的超常光学现象。通过对这些现象的研究,在光信息处理以及全光互联网等方面具有重要的理论和应用价值。为了突破衍射极限,基于表面等离激元(SPPs)的超构材料逐渐引起了广泛的关注。而以石墨烯为载体的阵列结构相比传统的金属阵列具有更多优势。对于中红外波长区的SPPs,石墨烯对其约束更强而损耗更小。除此之外,石墨烯材料的可调控性也是金属材料所不具有的。本论文中,分别以耦合波理论和频域有限差分方法对表面等离激元在石墨烯阵列中的成像与传播调控特性进行了对比分析,理论分析和数值模拟结果吻合的较好。主要的研究成果如下： (1)提出将耦合波理论用于解决在弱耦合条件下石墨烯阵列中表面等离激元的传播问题。建立了适用于石墨烯波导阵列的耦合波方程。并通过编写频域有限差分方法(FDFD)计算程序验证了该理论的正确性,为研究表面等离激元在石墨烯阵列中的传播提供了有效的理论支持。(2)首次提出了在弱耦合条件下石墨烯阵列中存在的离散表面等离激元泰伯效应。与连续的表面等离激元泰伯效应相比,泰伯距离可以通过调节石墨烯阵列的化学势和层间距而改变。泰伯距离可以缩小至入射波长的二十分之一,这是由于相邻波导中表面等离激元之间的耦合作用造成的。这种离散的表面等离激元泰伯效应在亚波长成像设备的制作方面有着广泛的应用前景。 (3)利用化学势渐变和介质宽度渐变两种不同结构的石墨烯阵列产生SPPs的空间布洛赫振荡。在这两种石墨烯阵列中,与传播方向垂直的方向上均有SPPs传播常数的梯度。第一种阵列中SPPs传播常数梯度是通过逐渐变化每个石墨烯的介电常数而获得。我们利用耦合波理论解析地得到了多波导激发方式下SPPs在阵列中的强度分布,展现了振荡模式的SPPs空间布洛赫振荡效应。用频域有限差分法模拟不同激发方式下SPPs在这两种波导阵列中传播,获得了与耦合波理论相吻合的结果。第二种石墨烯阵列通过逐渐变化石墨烯之间的介质层宽度而获得SPPs传播常数梯度,同样用FDFD模拟了多波导激发方式下SPPs在波导阵列中的强度分布。不同与前一种情况,多波导激发方式下SPPs仅呈现了简谐振荡效应。 (4)我们首次提出了在双周期石墨烯阵列中存在表面等离激元的颤振效应。通过传输矩阵方法和耦合波理论精确得到了该结构中SPPs的衍射曲线和带隙结构。用频域有限差分法模拟了SPPs在这种波导阵列中传播图像,获得了与耦合波理论相吻合的结果。其颤振运动的周期达到了微米量级而振幅也有几十个纳米,因而更便于在实验上进行观察。 (5)用800nm波长脉宽为50飞秒的激光器结合Z扫描方法研究了不同浓度的石墨烯溶液的非线性吸收和光限幅特性。样品表现出的大的反饱和吸收来源于双光子吸收机制。这种非线性特性导致当入射激光能量大于0.3J/cm2时,石墨烯样品归一化透过率显著减小,从而达到光限幅的目的。通过对不同浓度测量结果的比较,随着浓度的增加,这种非线性吸收效应逐渐增强,但当浓度超过10mg/L后,由于石墨烯薄片的聚集效应会造成非线性吸收效应减弱。
[Abstract]:Through the design of sub-wavelength micro-structure, the super-structure material can realize the control of equivalent electromagnetic parameters, so as to realize the regulation of superstructure material and light wave action mode. When light waves are transmitted, there are many extraordinary optical phenomena that are not observed in natural materials. Through the research of these phenomena, it has important theory and application value in the aspects of optical information processing and all-optical Internet. In order to break the diffraction limit, the super-structure material based on the surface plasmon excitation element (SPPs) has been widely used. and the graphene-based array structure has more traditional metal arrays than the traditional metal array, Advantages. For SPPs in mid-infrared wavelength regions, graphene is more constrained to its constraints In addition, the controllability of the graphene material is also not limited by the metal material. In this paper, the characteristics of imaging and propagation in graphene array are compared and analyzed by coupling wave theory and finite difference method in frequency domain respectively. Theoretical analysis and numerical simulation results are given. Good agreement. Major research. The results are as follows: (1) The theory of coupling wave is proposed to solve the surface of graphene array under weak coupling conditions. The propagation problem of the off-excitation element is solved. The method is suitable for the graphene waveguide. The coupling wave equation of the array is verified by the preparation of a finite difference method (FDFD) in frequency domain. The correctness of the theory is verified, and the propagation in the graphene array is provided for the research surface and the like. Effective theoretical support is presented. (2) The discrete surface existing in graphene array under weak coupling condition is proposed for the first time. The Talbot distance can be adjusted by adjusting the chemical properties of the graphene array compared with the continuous surface plasmon effect. the distance between the potential and the layer can be reduced to about one tenth of the length of the incident wave, which is due to the distance between the surfaces of the adjacent waveguides and the like, This discrete surface plasmon effect, such as the discrete surface plasmon effect, is in the production of sub-wavelength imaging equipment. wide application prospect is achieved. (3) S is generated by using a graphene array of two different structures with chemical potential gradient and medium width gradient; In both graphene arrays, in the direction perpendicular to the direction of propagation, The gradient of the propagation constant of SPPs. The gradient of the SPPs propagation constant in the first array is by gradually changing each In this paper, the intensity distribution of SPPs in array is obtained by coupled wave theory, and the SP of oscillation mode is shown. In this paper, we use the finite difference method in frequency domain to simulate the propagation of SPPs in these two waveguide arrays. In the second graphene array, SPPs propagation constant gradient is obtained by gradually changing the dielectric layer width between graphene, and the SPPs in multi-waveguide excitation mode are also simulated by FDFD. Intensity distribution in waveguide arrays. Different from the previous case, SPP in multi-waveguide excitation For the first time, we have proposed a two-cycle graphene array. The flutter effect of the surface plasmon is found in the structure. The transmission matrix method and coupled wave theory are accurately obtained in this structure. The diffraction curves and band gap structures of SPPs are simulated by the finite difference method in frequency domain. The results show that the cycle of flutter is on the order of microns and the amplitude is tens of nanometers. Therefore, it is more convenient to observe in the experiment. (5) The laser with 800nm wavelength pulse width of 50 femtosecond combines the Z-scan method to study the different concentrations. Nonlinear Absorption and Optical Limiting Properties of Graphene Solution Large anti-saturation absorption is derived from a two-photon absorption mechanism. This non-linear characteristic results in normalized penetration of graphene samples when the incident laser energy is greater than 0. 3J/ cm2. Through the comparison of different concentration measurement results, the nonlinear absorption effect gradually increases with the increase of concentration, but when the concentration exceeds 10mg/ L, the graphene sheet
【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ127.11

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