基于石墨烯的慢光波导研究

发布时间：2018-12-13 01:19

【摘要】：慢光波导是一种能有效减慢光信号传播速度而不改变光自身有效信息的新型光波导,由于其光缓存功能,已逐渐成为了光通信中的核心器件之一。近年来,宽带慢光已由光子晶体慢光波导、金属等离子体慢光波导等实现。然而,这些波导普遍存在带宽小的缺点,继而容易引发光信号在传输时的群速度色散,最终导致信号传输失真。此外,现有的慢光波导的性能动态不可调。为了解决这些问题,在本研究中我们设计了两种宽带、低色散、高品质因子(延迟带宽积)且性能动态可调的石墨烯宽带慢光波导。主要研究成果如下： 1.通过调研近十余年来的慢光波导文献,总结对比了不同结构慢光波导的性能后,我们发现目前的慢光波导带宽较小且波导性能动态不可调。为了获得更优越的波导性能,同时使波导动态可调,我们将研究重点集中在了石墨烯上,因为石墨烯同时具备高群折射率传播SPP波和可调性两大优势。我们根据近期石墨烯波导文献中提供的色散公式,绘制了单张石墨烯的色散曲线和群折射率图。分析后发现,石墨烯上传播SPP波的群折射率确实非常高,继而确认了石墨烯上可以传播慢光,为下一步的工作奠定了基础。 2.论证了石墨烯可传播慢光后,我们通过在石墨烯上构造周期性的空气孔来得到宽带慢光,并利用时域有限差分法来仿真模拟波导性能。首先,我们提出了光栅石墨烯慢光波导结构。在特定的波导结构参数下,当入射波导的谐振频率f从87THz至89THz范围变化时,波导慢光因子ng维持在(130+4)左右。在此区间内ng可认为是一个不变的常数值,即在此谐振频率范围内,波导呈现出宽带慢光的传输性质。此外,改变波导中石墨烯的化学势,即可动态调节慢光波导的各项性能指标,如其慢光因子ng、谐振频率f、带宽w等。 3.为了进一步简化波导结构,同时保持波导的优异慢光性能,我们又设计了三角孔石墨烯慢光波导。同样,在特定的波导结构参数下,当入射波导谐振频率f从90.15THz至90.75THz变化时,ng维持在107+5左右的数值,同时具备动态可调性。为了获得更大的延迟带宽积NDBP、慢光因子ng、带宽w等,我们仿真记录了每组波导三角孔参数Wg、Ws变化下的波导性能数据。分析对比后,最终可得的最大波导延迟带宽积NDBP达0.96,极大地提高了现有波导的慢光性能。
[Abstract]:Slow optical waveguide is a new type of optical waveguide which can effectively slow down the propagation speed of optical signal without changing the effective information of light itself. Because of its optical buffer function, slow optical waveguide has become one of the core devices in optical communication. In recent years, broadband slow light has been realized by photonic crystal slow optical waveguide and metal plasma slow optical waveguide. However, these waveguides generally have the disadvantage of small bandwidth, which can easily lead to the group velocity dispersion of the optical signal during transmission, and eventually lead to the distortion of the signal transmission. In addition, the performance of the existing slow optical waveguides is unadjustable. In order to solve these problems, we have designed two kinds of graphene broadband slow optical waveguides with low dispersion, high quality factor (delay bandwidth product) and dynamic tunable performance. The main research results are as follows: 1. By investigating the literature of slow optical waveguides in recent ten years and comparing the performances of slow optical waveguides with different structures, we find that the bandwidth of slow optical waveguides is small and the dynamic performance of waveguides is not adjustable. In order to obtain better waveguide performance and make waveguide dynamic adjustable, we focus on graphene, because graphene has the advantages of both high group refractive index propagating SPP wave and tunability. Based on the dispersion formula provided in recent graphene waveguides, the dispersion curves and group refractive index diagrams of single graphene are plotted. It is found that the group refractive index of SPP wave propagating on graphene is very high, and it is confirmed that slow light can be propagated on graphene, which lays a foundation for further work. 2. It is proved that graphene can propagate slow light, we obtain broadband slow light by constructing periodic air holes in graphene, and simulate the performance of waveguide by using finite-difference time-domain (FDTD) method. Firstly, we propose a grating graphene slow optical waveguide structure. When the resonant frequency f of the incident waveguide varies from 87THz to 89THz, the waveguide slow light factor (ng) is maintained at (1304) under certain waveguide structure parameters. In this region, ng can be regarded as a constant value, that is, in the range of resonance frequency, the waveguide exhibits the propagation property of broadband slow light. In addition, by changing the chemical potential of graphene in the waveguide, we can dynamically adjust the performance of the slow optical waveguide, such as the slow light factor ng, resonance frequency f, bandwidth w and so on. 3. In order to further simplify the structure of the waveguide and maintain the excellent slow optical properties of the waveguide, we have also designed the triangular hole graphene slow optical waveguide. Similarly, when the resonant frequency f of the incident waveguide varies from 90.15THz to 90.75THz, the value of ng is about 107.5, and it has dynamic tunability under certain waveguide structure parameters. In order to obtain larger delay bandwidth product (NDBP,) slow light factor (ng,) bandwidth w and so on, we simulated and recorded the waveguide performance data of each set of waveguide triangulation hole parameters Wg,Ws. After analysis and comparison, the final maximum waveguide delay bandwidth product (NDBP) is 0.96, which greatly improves the slow optical performance of the existing waveguides.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN252

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