亚波长介质光栅设计简化模式法的修正及相关研究

	亚波长介质光栅设计简化模式法的修正及相关研究
	王斌
学位类型	博士
导师	吴一辉
	2014-07
学位授予单位	中国科学院大学
学位专业	机械制造及其自动化
摘要	亚波长介质光栅是伴随纳米制造技术发展起来的一种新型光栅。它具有高衍射效率的特点，因此在光通讯、光计算、全息摄影、光学度量、激光脉冲压缩等光学元器件中有重要应用,相关研究受到广泛关注。为提高亚波长介质光栅设计的计算效率，提高其结构性能的可预见性，本文重点开展了其简化算法的研究。在对影响严格耦合波法（RCWA）计算精度的因素进行分析的基础上，提出采用该方法所获光栅衍射效率作为光栅设计理论值的条件及误差参考。对已有简化模式法（SMM）进行了深入分析并与RCWA计算结果进行了对比研究，找到了已有的SMM算法计算误差较大的原因；以三角形介质光栅为例，提出了一种从多层膜反射和薄膜导纳刻画各个模式反射率的修正算法（MSMM），利用该新型物理模型修正后的计算结果与RCWA的计算结果对比分析表明，修正后的MSMM方法与RCWA的计算偏差大大缩小。利用该方法，通过计算光栅导纳随光栅周期的变化规律，分别对矩形和三角形光栅的衍射效率进行了研究。矩形光栅导纳随着占宽比变化仅在空气导纳附近较小范围内，说明亚波长矩形介质光栅的反射率和光栅的占宽比相关性较小；通过分析得出矩形介质光栅无法得到接近100%的透射效率。给出了入射角一定的情况下，不同周期的三角形光栅反射率的变化规律。以此为基础设计出TE偏振和TM偏振同时能达到衍射效率超过99.9%的三角形介质光栅。应用MSMM分析了光栅衍射效率和光栅结构参数之间的关系，并优化设计出双端口光栅分束器。研究了光栅的矩形结构、三角形结构在偏振无关、偏振相关情形下的分束性能。设计得到的偏振无关光栅分束器在1020nm-1100nm波段，TE波和TM波的0级和-１级衍射效率都在50%左右；偏振相关分束器在该波段的消光比也都在10以上。对于亚波长三角形、正弦形和矩形介质光栅，该方法将衍射效率表达成相位差偏移和光栅与空气导纳之差引起的反射，比RCWA更直观的展示了光栅衍射的物理过程。相比只提供初值的SMM，MSMM可以直接用来进行优化计算。因此该算法对于加深对该类介质光栅的认识以及设计优化具有积极作用。
其他摘要	Dielectric subwavelength grating is a new type grating developing with evolution of nano technology. Because of high efficiency, it is used frequently in optical communication, computation, metrology, holography, laser pulse compression and so on. Many researchers focused on this issue. For the purpose of increasing the speed of calculation in designing dielectric subwavelength gratings and giving a good prediction of grating structure, the simplified method will be researched in this paper. In this paper, the factors of computational accuracy are analyzed when the rigorous coupled wave analysis (RCWA) method is used to design a grating. This analysis shows the result that RCWA could be used to be a reference as a theoretical value for other algorithm in grating design. The simplified modal method (SMM) is analyzed and the deviation between SMM and RCWA is calculated to find the reason of its big error. Take a triangular grating as an example, which is seen as multilayer films and the each layer owns a new effective index. The reflection and transmission of grating could be characterized by optical admittance of the films. Then formulas of grating transmission in SMM are modified by reflection. The calculation by this modified simplified modal method (MSMM) is a better approximation to RCWA than other methods. Based on MSMM, for a rectangular grating, although the admittance changes with duty cycle, its variation range is very near the admittance of air. This means the reflection of rectangular grating will not change a lot when duty cycle is changed. And a rectangular grating cann’t get transmission efficiency near 100%. Then the mode indices and admittance versus the period of triangular gratings and the duty cycle of rectangular grating are analyzed. A grating with transmission efficiency more than 99.9% for both TE and TM-polarized light is designed. The relations between grating structure and transmission efficiency are analyzed by MSMM. The splitting result of rectangular and triangular grating are analyzed for both TE and TM polarization.Based on these calculations, 1×2 beam splitters are designed and optimized by MSMM. A polarization-independent splitter grating will get a good splitting result at the band 1020nm-1100nm. The transmission efficiency of 0th and -1st order for both TE and TM polarization is near to 50% at this band. The extinction ratio of a polarization-dependent splitter is bigger than 10 at this band. Contrast to RCWA, MSMM gives a clear physical explanation of grating diffraction by considering the transmission efficiency as the result of phase shift of modes and difference of grating admittance and aerial admittance. This method can be applicable to triangular, sinusoidal and rectangular gratings. Because it can be used to optimize the grating parameters directly, MSMM is better than SMM which only gives starting value of grating parameters. Thus MSMM gives a good understanding on dielectric subwavelength gratings and is useful in designing and optimizing them.
语种	中文
文献类型	学位论文
条目标识符	http://ir.ciomp.ac.cn/handle/181722/41473
专题	中科院长春光机所知识产出
推荐引用方式 GB/T 7714	王斌. 亚波长介质光栅设计简化模式法的修正及相关研究[D]. 中国科学院大学,2014.

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