载入中....
设为首页 收藏本站 联系我们 网站地图
论文网
您现在的位置: 免费毕业论文网 >> 理学论文 >> 光信息科学 >> 正文
搜索: 论文

周期性介质中宽带无色散慢光关键技术研究

更新时间 2009-9-6 12:32:42 点击数:

周期性介质中宽带无色散慢光关键技术研究
Research on Key Technology of Broadband Dispersionless Slow Light in Periodic Medium
【中文摘要】 本论文主要对周期性介质结构中宽带无色散慢光的关键技术进行研究。设计了三种不同类型的慢光波导,实现了室温下低群速度低色散的宽带慢光传播。本研究工作对于推动以慢光为基础的集成光子器件的发展具有重要意义。本论文的主要研究内容如下:第一章为绪论,主要对本论文所涉及的理论基础和研究背景进行了综述。首先介绍了慢光技术的应用领域,及一些与慢光相关的基础知识。其次,对几种比较典型的实现慢光的机理,如:电磁感应透明技术(EIT)、相干布居振荡(CPO)、谐振耦合技术(CRS)进行了分析与比较。最后,介绍了慢光波导的研究进展,为我们后文的研究及设计提供理论依据。论文的第二章设计了一种基于六角形晶格的二维光子晶体线缺陷波导,在结构上作了一定的创新。在线缺陷中,引入了一排椭圆型的空气孔,同时,通过改变与线缺陷相邻的外围圆型空气孔半径来调整波导的传输性能。通过适当的调谐与线缺陷相邻的空气孔的结构参数,得到了波导的最优结构。此时,波导的群速度最小,约为0.0018c,同时群速度色散(GVD)也达到最小,低于105(a/2πc2)数量级,大大降低了传输过程中信号产生的失真。接着,从色散曲线、品质因数Q、有限差分(FDTD)仿真三方面对此波导的特性进行研究。色散曲线的拐点从理论上证明了此波导的群速度和GVD同时达到零,105数量级的高品质因数说明光脉冲在此波导中驻留的时间很长,时域的场强分布图再一次证明无论从纵向还是横向来看,光信号都被很好的限制在波导中央,无色散地以极慢的光速传播。论文的第三章考虑了带宽的影响,设计了另一类结构更为简化的慢光波导,可以获得更大的延迟带宽积(DBP)。此类波导放弃了传统的二维光子晶体线缺陷波导结构,以更为简洁的空气孔阵列直波导为基础,设计了两种新颖的空气孔结构。一种采用椭圆型空气孔,另一种采用两个半椭圆交叠而成的沙漏型空气孔。本章分别从能带结构和FDTD仿真两方面分析了这两种新型的空气孔阵列直波导。对于椭圆型波导,得到其平均群指数n%g为418,DBP达到0.166。而对于沙漏型波导,其平均群指数n%g为87.7,DBP达到0.186。经过与前人的研究成果进行比较,结果证实此波导的设计不仅结构较为简单,而且在DBP上也有不小的提高,进一步论证了这两种新型波导的优越性。论文的第四章突破了群速度与带宽之间的固有限制,设计了一种新型的基于光子晶体线缺陷波导的级联型谐振腔波导结构,数值仿真实现了超大带宽的慢光传输。本章首先考察了一种结构较为简单的单一谐振腔波导。通过对其能带的计算与分析,得到了一条极其平坦的色散曲线,满足群速度和GVD都同时接近于零。接着,将四种具有不同共振频率的谐振腔组合在一起,设计了一种级联型的波导结构。此波导可以得到四条十分接近且平坦的能带,其最大和最小能带之间的差近似等效为一无色散超慢光模的带宽。平均群指数n%g为833,相对频率带宽dω/ω等于2.22×10-2,相当于4.3THz。FDTD的仿真结果也很好地证实了这一波导的慢光特性。此类波导还可以进行拓展,通过增加级联的谐振腔数量,同时减小相邻谐振腔之间的频率间隔来实现一近似连续的具有超大带宽的慢光模式。这对于传统的群速度与带宽的限制来说,是一个极大的突破。论文的第五章考虑到波导实际的制备工艺,在上一章级联波导的设计思路下,采用基于空气孔排布的六角形晶格结构。本章首先研究一种比较普遍的基于实芯线缺陷波导的谐振腔波导结构,波导中心的线缺陷采用与背景相同的介质材料。结果发现当谐振腔内空气孔半径发生改变时,所产生的能带平移量非常小,这对于宽带的应用来说是远远不够的。为了解决这一问题,本章接着引入了空气芯线缺陷,通过降低波导中心的介电常数,使光脉冲更容易耦合到两边的谐振腔内,从而可以得到较大的频率偏移。本章接着提出一种对称型的双谐振腔波导,通过对其色散曲线和场强分布的研究,发现这种结构确实可以产生两条平坦且相近的能带。于是,最后本章提出了改进的基于空气芯线缺陷的级联型谐振腔波导,在相邻的四个谐振腔内依次引入四种不同的空气孔半径,从色散曲线上来看,可以得到四条异常平坦的能带,相对频率带宽dω/ω也可以达到2.02×10-2。相对应的静态场分布也很好地证实了这一设计思路,与谐振腔频率相同的信号分量均耦合入相应的谐振腔内。论文的第六章对第五章提出的基于空气芯线缺陷的级联谐振腔波导结构进行了进一步改进,将波导中心的空气芯线缺陷用SiO2线缺陷来代替,数值实现同样的超宽带慢光传输的同时,避免了制备时在第三维度上的耗散。与上两章的分析过程类似,本章首先研究了单一的谐振腔波导。通过对其能带的计算与分析,得到了一条异常平坦的色散曲线。同时,通过考察谐振腔内空气孔的不同半径对色散曲线的影响,发现能带的平移量满足设计中对超宽带的要求。接着,本章提出改进的基于SiO2线缺陷的级联型谐振腔波导,在相邻的四个谐振腔内依次引入四种不同的空气孔半径,并从色散曲线、场强分布和FDTD仿真三方面分析了这种新型波导的性能。其色散曲线和对应的静态场分布很好地证实了这一设计思路,与谐振腔频率相同的信号分量均耦合入相应的谐振腔内。通过计算,得到此波导的平均群指数n%g为909,平均GVD参数D约为4.1(ps/(nm·mm)),相对频率带宽dω/ω等于2.02×10-2,相当于有效带宽为3.9THz。FDTD仿真结果都很好地证实了这一理论分析。论文的第七章提出了对波导设计进行优化设计的方法。通过引入遗传算法,同时嵌入能带计算的平面波展开法,设计了一种对波导结构参数进行优化,以达到最小群速度的优化算法。此优化算法的基本原理是:首先,设定待优化的波导结构参数为特定基因组,通过编写适应值度量函数来计算对应波矢的群速度,最后通过控制遗传算法来获得最小的群速度和最佳的波导结构。大大简化了以后的慢光波导设计流程,提高了设计的精确度。最后,第八章对全文的结论和创新点进行了总结,并提出了未来的研究重点

【英文摘要】 This dissertation studies the key technology of broadband dispersionless slow light in periodic medium. Three types of novel slow mode waveguides are proposed to realize the low-group-velocity low-dispersion wide-band slow-mode propagation under room temperature, which could lead to a number of important fundamental and technological advances in the field of slow light communication.This dissertation is organized as follows:Chapter 1 first introduces the applications of the slow light technologies and presents fundamental theories. Then we describe the mechanisms to achieve slow light, focusing on the analysis and comparison among EIT, CPO and CRS. Last, we introduce the current development of the slow mode waveguide. These concepts and theories are necessary for the following research work.In Chapter 2, we propose and evaluate a two-dimensional photonic crystal waveguide with two line defects separated by a row of elliptic air holes. By adjusting the structural parameters, we obtain a waveguide with an inflection point on the dispersion curve corresponding to a slow-light mode with reduced distortion. The group velocity, around 0.0018c, and the GVD parameter, less than the order of the magnitude of 105(a/2πc2) both reach minimum. Moreover, we investigate the transversely confined field and high quality factor, which both indicate that the dispersionless slow wave can be generated in our wave guide.In Chapter 3, we take the bandwidth of the waveguide into account, and design two novel air-hole-array strip waveguides, one with elliptic air holes and the other with sandglass-shaped ones, in order to simplify the structures of the devices and obtain the larger delay-bandwidth-product (DBP). The band diagram and FDTD simulation results both prove that the flatband modes with low group velocity and low dispersion can be obtained. As for the waveguide with elliptic air holes, average group index could reach 418, and DPB equals to 0.166. As for the other with sand-glass shaped air holes, average group index equals to 87.7, and DBP reaches 0.186. Each waveguide has its strong point, one can choose the lower group velocity and narrow bandwidth (one with elliptic air holes) or higher group velocity and wide bandwidth (one with sandglass-shaped air holes), according to the application. Moreover, the structures we proposed are compared with that reported in literatures, and show our structures yield a significant increase in DBP.In Chapter 4, we design a novel cascaded line defect photonic crystal waveguide with different cavities on two sides to break the trade-off between group velocity and bandwidth, realizing the slow light propagation with ultra wide band by simulation. First we investigate a simple line defect photonic crystal waveguide with the same cavities, and achieve an extremely flat band, satisfying both the small group velocity and vanishing GVD. Then, by introducing four different cavities on sides with different radii, a novel cascaded waveguide is proposed. There truly exist four close flat bands on the dispersion curves, which could be regarded equivalently as a wide bandwidth. Operating in the band, we can achieve slow light with ultra low group velocity (c/800) and low dispersion. Simulation is carried out to demonstrate the slow light propagation in the novel waveguide. Compared with conventional structures, our design has a breakthrough on the contradiction between low group velocity and wide bandwidth. The effective bandwidth of our structure could reach 4THz. And one could reduce the increment of the neighboring bands by decreasing the difference between the radii of the cavities, or expand the bandwidth by cascading more different cavities. In Chapter 5, we take the fabrication of the waveguide into account, and propose a waveguide with the triangle lattice of air holes, following the idea of the wideband design in the above chapter. First we investigate a commonly used structure with a line defect of the same index as the background in the middle, and find there is a series of close flat bands. However, the shift of the bands caused by the change of the radius of the air hole in the cavity is too tiny to meet the needs of wide band propagation. To solve this problem, we introduce a line defect made of air to enlarge the shift of the bands by reduce the inflection index in the middle of the waveguide. Then we propose a structure with dual cavities, and demonstrate two close and flat bands by the study of the dispersion curve and field distribution of this waveguide. At last, by introducing four different cavities on sides with different radii, a novel cascaded waveguide is proposed. There truly exist four close flat bands, which could be regarded equivalently as a wide bandwidth. The bandwidth of our structure could reach 2.02×10-2. Simulation of the static field distribution is carried out to demonstrate the slow light propagation in the novel waveguide.In Chapter 6, we improve the cascaded waveguide, which is proposed in Chapter 5, by replacing the line defect made of air with that made of SiO2, in order to avoid the dissipation on the third dimension for application. Similar with the analysis in the above two chapters, in this chapter, we first investigate the waveguide with the same cavities, and achieve an extremely flat band, satisfying both the small group velocity and vanishing GVD. Then we propose a structure with dual cavities, and demonstrate two close and flat bands by the study of the dispersion curve and field distribution of this waveguide. At last, by introducing four different cavities on sides with different radii, a novel cascaded waveguide is proposed. There exist four close flat bands. Operating in the band, we can achieve slow light with ultra low group velocity (c/900) and low dispersion. Simulation is carried out to demonstrate the slow light propagation in the novel waveguide. The effective bandwidth of our structure could reach 4THz.In Chapter 7, we propose an optimal approach on the design of the waveguide. By introducing the genetic algorithm into the band solving method, we design an optimal method on working out the structural parameters to obtain the minimal group velocity. The principal of the optimal method is: first set the structural parameters as the specific genes, and then write the evaluation function to calculate the goup velocity, and last control the genetic algorithm to achieve the minimal group velocity and the optimized structure of the device. This highly simplifies the design procedure of the slow mode waveguide.Chapter 8 summarizes the results of this work. Future research topics for the fabrication and optimize of the slow light waveguides are proposed.

【中文关键词】 慢光; 群速度色散; 延迟带宽积; 光子晶体
【英文关键词】 slow light; group velocity dispersion; delay-bandwidth product; photonic crystals
论文目录】
摘要 3-6
ABSTRACT 6-9
1 文献综述 13-40
    1.1 慢光技术的应用 13-14
    1.2 慢光基础 14-17
        1.2.1 相速和群速 14-15
        1.2.2 脉冲失真 15-17
    1.3 慢光的实现机理 17-28
        1.3.1 电磁感应透明(EIT) 17-21
        1.3.2 相干布居振荡(CPO) 21-24
        1.3.3 耦合谐振技术(CRS) 24-26
        1.3.4 其余慢光机制 26-28
    1.4 慢光波导的研究 28-38
        1.4.1 光子晶体的研究方法 29-32
        1.4.2 慢光波导的研究进展 32-38
    1.5 本章小结 38-40
2 基于光子晶体线缺陷波导的低色散慢光的设计与分析 40-53
    2.1 研究背景 40-41
    2.2 波导结构设计与优化 41-44
    2.3 数值分析与仿真 44-51
        2.3.1 群速度与GVD 参数β2 44-47
        2.3.2 品质因数Q 47-49
        2.3.3 FDTD 仿真 49-51
        2.3.4 比较 51
    2.4 本章小结 51-53
3 基于空气孔阵列直波导的平坦能带慢光的分析与实现 53-63
    3.1 研究背景 53
    3.2 传统圆型空气孔阵列直波导的研究 53-55
    3.3 新型椭圆型空气孔阵列直波导的设计与分析 55-58
        3.3.1 群速度与GVD 参数 55-57
        3.3.2 FDTD 仿真 57-58
    3.4 新型沙漏型空气孔阵列直波导的设计与分析 58-61
        3.4.1 群速度与GVD 参数 58-60
        3.4.2 FDTD 仿真 60-61
    3.5 比较与讨论 61
    3.6 本章小结 61-63
4 基于介质柱背景的级联型谐振腔波导中宽带慢光的研究与分析 63-74
    4.1 研究背景 63
    4.2 设计方法 63-69
        4.2.1 单一谐振腔波导的研究 63-67
        4.2.2 新型级联型谐振腔波导的设计 67-69
    4.3 数值分析和仿真 69-73
        4.3.1 色散曲线 69-71
        4.3.2 静态场分布 71
        4.3.3 FDTD 仿真 71-73
    4.4 本章小结 73-74
5 基于空气孔背景的级联型谐振腔波导中宽带慢光的研究与分析 74-88
    5.1 研究背景 74
    5.2 基于实芯线缺陷波导的谐振腔波导研究 74-78
    5.3 基于空气芯线缺陷波导的谐振腔波导研究 78-87
        5.3.1 单一谐振腔波导的研究与分析 78-80
        5.3.2 对称型双谐振腔波导的研究与分析 80-83
        5.3.3 级联型谐振腔波导的研究与分析 83-87
    5.4 本章小结 87-88
6 改进的基于SiO_2 线缺陷波导的级联谐振腔波导中宽带慢光的研究与分析 88-100
    6.1 研究背景 88-89
    6.2 设计方法 89-95
        6.2.1 单一谐振腔波导的研究与分析 89-91
        6.2.2 对称型双谐振腔波导的研究与分析 91-94
        6.2.3 新型级联型谐振腔波导的设计 94-95
    6.3 数值分析和仿真 95-98
        6.3.1 色散曲线 95-96
        6.3.2 静态场分布 96-97
        6.3.3 FDTD 仿真 97-98
    6.4 本章小结 98-100
7 基于光子晶体能带计算的优化算法研究与实现 100-110
    7.1 研究背景 100
    7.2 相关算法 100-103
        7.2.1 平面波展开法 100-101
        7.2.2 遗传算法 101-103
    7.3 软件实现 103-107
        7.3.1 适应值度量函数的编写 103-106
        7.3.2 遗传算法的控制 106-107
    7.4 实例测试与结果分析 107-109
        7.4.1 测试案例 107-109
    7.5 本章小结 109-110
8 论文总结 110-115
    8.1 研究工作总结 110-112
    8.2 未来研究展望 112-113
    8.3 论文创新点 113-115
参考文献 115-122
致谢 122-123
攻读学位期间的学术论文和专利 123-126
上海交通大学学位论文答辩决议书 126

返回栏目页:光信息科学论文

设为主页】【收藏论文】【保存论文】【打印论文】【回到顶部】【关闭此页