【作者】 陈娟；

【导师】 闫连山；

【作者基本信息】 西南交通大学 ， 信号与信息处理， 2012， 硕士

【摘要】 亚波长一维金属光栅具有集成度高、偏振特性好、光谱较宽、透射率和消光比较高等优点,在改进和取代传统光栅元件方面有很大的潜力,因而引起了广泛的研究兴趣。基于亚波长纳米工艺技术的表面等离子(SPP)偏振态控制研究是传统偏振态研究的一个突破,但是由于一维金属光栅表现出明显的双折射效应,使得这种光栅的应用范围受到了限制。论文将一维光栅的等效介质理论(EMT)推广到二维亚波长结构,建立了金属表面等离子偏振控制器模型,实现任意线偏振入射光的高透射。首先,介绍了金属光栅结构基于麦克斯韦方程组的两种数值计算方法：时域有限差分法(FDTD)和严格耦合波法(RCWA)。通过理论分析及仿真计算,分析了二维金属光栅的结构参数设计问题,包括二维正方形金属光栅和二维矩形金属光栅在两个方向上的周期、占空比、槽深、入射光波长对输出光偏振态及透射特性的影响。其次,利用时域有限差分(FDTD)算法,对一种特定的二维矩形金属光栅结构进行了分析,并对输出光偏振态和透射特性进行了仿真。在优化结构参数下,当入射光(波长为550nm)垂直入射的线偏振角为30°时,仿真结果实现了由输入线偏振态到输出圆偏振态的转换。再次,参考二维矩形金属光栅在实现圆偏振输出时的结构参数,通过空间角调制的方法,实现了对二维矩形金属光栅由输入线偏振到输出任意偏振态的控制。仿真结果表明：输出光的偏振态理论上可实现全庞加莱球覆盖,并具有较高的透射率。最后,综合等效介质理论和表面等离子激元(SPP)Bloch模型,对比分析了两种亚波长光栅结构：二维矩形金属光栅和二维椭圆柱金属光栅。对比分析了两种结构的透射率及其相位延迟与入射光波长及偏振角的关系,尤其是两种结构在实现1/4波片功能对应的透射特性。仿真结果表明,在入射光偏振角为75°时,此时二维矩形和椭圆柱金属光栅的透射率分别为0.77和0.67,表明二维矩形金属光栅比二维椭圆柱金属光栅在实现1/4波片的功能上具有更好的透射效果。对应550nm-800nnm的入射光波长,两种光栅在各自允许的入射角范围内均表现了较为平坦的宽带透射特性。提出的二维金属光栅结构在偏振及高透射等特殊功能的光子集成器件中具有广泛的应用前景,包括光纤通信、光互联、数据存储和成像等领域。更多还原

【Abstract】 One-dimensional subwavelength metallic gratings have been considered as one of the most promising ways to improve and replace the traditional grating components for their advantages of high integration, excellent polarization properties, wide spectrum, and high transmittance and extinction. Thus, the plasmonic gratings have received great deal of interest from the researchers. Surface plasmon polaritons (SPPs) polarization control based on the subwavelength nanometer process technology is a breakthrough of the traditional polarization state research. However, the one-dimensional subwavelength metallic gratings are limited in the polarization application because of its birefringence effect. In this paper, based on the equivalent medium theory (EMT) of two-dimensional subwavelength grating which is promoted from that of one-dimensional structure, a plasmonic metallic polarization control structure is proposed. The arbitrary polarized state between TE and TM input waves are achieved with high transmittance.First of all, we introduce two numerical methods for the metallic grating structure. These methods are based on the Maxwell equations:finite difference time domain method (FDTD) and rigorous coupled-wave method (RCWA). Through the theoretical analysis and simulation, the influence of the design parameters on the polarization and the transmittance are discussed in detail, including the groove depth, the period and the duty cycle of the square and rectangular metallic grating along x-axis and y-axis directions, as well as the incident wavelength.Secondly, a proposed two-dimensional metallic rectangular grating is simulated based on the FDTD method, and the polarization transformation and the transmittance are obtained. With the optimized structure parameters, the simulation results show that the conversion of linear input to circular polarization state output is realized, when the linearly polarized light (wavelength of550nm) normally incidents on the proposed two-dimensional nano-structure with the polarization angle of30°.Thirdly, reference to the parameters of the grating with circular polarization state output, the characteristics of polarization and transmittance are achieved by space angle modulation. Simulation results show that the full Poincare sphere coverage could be obtained theoretically, and a high transmission is achieved as well.Finally, based on the equivalent medium theory and the SPP Bloch model, two kinds of novel metallic waveplates are analyzed with optimized parameters:two-dimensional rectangular metallic gratings and elliptical pillars metallic gratings. Firstly, for these two structures, the relationships of the transmittance and phase retardation to the incident light and the polarization angle are compared and analyzed. Especially, the transmission properties are studied in detail, when both of the gratings are performed as quarter-wave plates. The simulation results show that both structures can act as quarter-wave plates when the input polarization angle is75°. The corresponding transmittances of rectangular and elliptical cylinder grating are0.77and0.67, respectively. In addition, both gratings exhibit relatively flat transmission spectra within the wavelength range from550nm to800nm in the presence of different input polarization angles.Two-dimensional metallic grating structures proposed in this paper have extensive application prospects in polarization and high transmittance of photonic integrated devices. They can be used in the field of optical fiber communication, optical inter-connects, data storage and imaging.更多还原