| 题名 | 光栅简化模式方法及应用 |
| 作者 | 郑将军 |
| 学位类别 | 博士 |
| 答辩日期 | 2009 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 周常河 |
| 关键词 | 模态法 时域有限差分方法 耦合波方法 光栅分束器 光栅对压缩装置 泰伯效应 |
| 其他题名 | Simplified Modal Method of Gratings and Applications |
| 中文摘要 | 光栅是最基本的周期性结构，自发明以来，便被广泛的研究和应用。目前，光栅的种类繁多，加工技术和数值模拟技术发展的成熟，使得我们可以对光栅进行前所未有的深入研究。本博士论文主要包含以下几个方面的工作： 1) 基于简化的模式理论，设计了一系列高效率的高密度相位型光栅分束器。简化的模式理论，是指忽略对衍射过程影响小的倏逝波模式，分析被衍射级次同被激发的传播模式之间的能量交换过程，揭示衍射的物理图景。利用简化模式理论，我们揭示了二次布拉格较入射下，矩形光栅的衍射主要取决于三个传播的光栅模式。基于模式分析，设计了高效率-2级衍射器件，1×2分束器及1×3分束器，并且研究了偏振相关的衍射特征。二次布拉格角入射情形相对垂直入射情形，具有更强的偏振相关性。该工作发表在[JOSA A, Vol. 25, No. 5, 1075-1083 (2008)]上。研究了三角槽形的熔融石英偏振分束器。将光栅内部的衍射描述为奇对称和偶对称模式的独立传播过程，提出平均有效折射率的概念，给出了偏振分束器设计条件。直接利用设计条件，得到了理论衍射效率～99％，且消光比极高的偏振分束器。该工作发表在[Optics Letters, Vol. 33, No. 14, 1554-1556 (2008)]上。提出基于金属层反射的反射式的偏振分束器，利用模式分析了其衍射过程，用作图法得到1550nm波长下的高效率反射式偏振分束器。对于复杂结构光栅，作图法不易获得最优解，所以，结合模拟退火算法，获得了1500－1600nm波段下的宽带高效率偏振分束器件。该工作发表在[J. Opt. A: Appl. Opt., Vol. 11, 015710 (2009)]上。提出并设计了双层的光栅偏振分束器，相对单层的光栅偏振分束器，该双层的光栅偏振分束器可获得更高的衍射效率，具有更宽的带宽。更重要的是，设计上具有极大的灵活性。光栅层之间的模式反射和透射，使用简化的模式方法做出了细致的分析。该结果将发表在Optics Communications 2009上。 2) 提出并设计了倍密度光栅对装置用于压缩飞秒脉冲和构造飞秒双脉冲。该装置使用了低密度光栅对，第二块光栅的密度是第一块的两倍，用于将入射光原路返回。选择合适密度的光栅以及合适的工作距离，该光栅对可以提供匹配的负群速色散量，从而将啁啾高斯脉冲压缩成其傅立叶变换极限的脉冲。实验和理论上分析了飞秒脉冲经过该光栅对装置后的特性。若使用两路结构，其中一路的第二块光栅置于微动平台上，则可以用于构造飞秒双脉冲。该倍密度光栅对装置提供的是比传统光栅对装置小得多的色散量，相对传统的棱镜对装置，它质量轻，体积小，结构简单，操作方便。该工作发表在[JOSA B, Vol. 24, No. 4, 979-984 (2007)]上。 3) 运用矢量的方法研究高密度光栅的近场泰伯效应。由于高密度光栅周期可同波长相比，只能使用矢量方法来模拟和分析。针对所谓的“偏振泰伯效应”，我们使用严格耦合波方法和时域有限差分方法，均得到了一致的结果，通过比较分析整幅和相位的影响，提出相位是影响该近场偏振相关图像的关键原因，实验上使用泰伯近场扫描显微镜技术验证了理结果。该工作发表在[Optics Communications, Vol. 281, 3254-3259 (2008)]上。此外，运用傅立叶分解和严格耦合波方法，研究了飞秒光入射下，高密度光栅近场泰伯像随着脉冲宽度和探测距离变化而变化的特征。发现高密度光栅的泰伯像对比度随脉冲宽度的变化更加明显，且当探测距离足够远的时候，对比度保持不变，这个临界距离同脉冲的宽度相关。该工作发表在[Optics Communications, Vol. 281, 3230-3236 (2008)]上。 本博士论文，包括了以上我们在光栅分束器、光栅对压缩器和高密度光栅泰伯效应上的主要研究结果。它们将加深人们对光栅衍射过程的认识，有益于光栅的应用。对微纳结构光栅及基于光栅的装置的研究，还会继续深化。 |
| 英文摘要 | A grating is the most basic periodic structure, which has been widely used for various applications. At present, there are various kinds of gratings. As the fabrication techniques and numerical simulation techniques have been highly developed, the research on gratings can be unprecedented advanced. Several research aspects on gratings are included in this doctoral dissertation: 1) A series of highly efficient high-density phase garting beamsplitters are investigated by using the simplified modal method. The simplified modal method means that evanescent grating modes neglected due to their minor contribution to the diffraction process, the physical image of the diffraction will be revealed by analyzing the energy exchange between the diffraction orders and the excited propagating modes. For binary phase grating under 2nd Bragg angle incidence, the diffraction behaviors are dominated by three propagating grating modes. Based on the modal analysis, high-efficiency-2nd-order diffraction elements, 12 beamsplitters, and 13 beamsplitters are designed. The polarization dependency is analyzed. Compared to normal incidence, the case of second Bragg angle incidence shows stronger polarization effects. This work is published on [JOSA A, Vol. 25, No. 5, 1075-1083 (2008)]. A deep triangular fused-silica grating is illustrated as a polarizing beam splitter (PBS). The light propagation inside the grating is shown to be independent for the even and odd modes. The efficiency can be ~99%, and the extinction ratios are very high. This work is published on [Optics Letters, Vol. 33, No. 14, 1554-1556 (2008)]. A metal-mirror-based reflecting PBS is proposed. A modal analysis is done to reveal the diffraction process. By graphic method, a reflecting PBS is obtained for operation at 1550nm. Since the grating structure is complicated with several geometrical parameters, it is not easy to find the optimum design with the graphic method directly. By using the well- known simulated annealing method, a reflecting PBS for operation over the wideband 1500-1600nm is obtained with high efficiencies and extinction ratios. This work is published on [J. Opt. A: Appl. Opt., Vol. 11, 015710 (2009)]. To improve the design flexibility and performance, a two-layer grating is investigated as a transmission PBS. The reflection and transmission effects on the interfaces are given a detailed theorectical modal analysis. Design equations are given. This related paper has been accepted by Optics Communications 2009. 2) A double-line-density grating pair is proposed for compression and generation of double femtosecond laser pulses. This structure uses two low-density gratings. The period of the second grating is twice of that of the first grating, which is used to retroreflect the incident beam. By selecting the gratings with proper density and the proper working distance, the double-line-density grating structure can provide matched dispersion to compress a Gaussian pulse to its Fourier-transform-limitted form. The performance of the grating structure is demonstrated both in theory and in experiments. If a two-arm structure is used with the second grating in one arm mounted on micro-moving stage, the structure can be used to generate double femtosecond pulses. The double-line-density grating structure provides much less group-velocity dispersion than a classical grating pair. Compared with a classical prism pair, it has less weight and smaller volume. It is simple in structure and easy for operation. The work is published on [JOSA B, Vol. 24, No. 4, 979-984 (2007)]. 3) The near-field Talbot effect of high-density grating is investigated by using vecotor method. Because the high-density grating has a period in the order of the wavelength, the vector methods should be employed. For the so-called “polariztion- dependent Talbot effect”, the same results can be obtained by using the rigorous coupled-wave method and the finite-difference time-domain method. By analyzing the influence of field amplitudes and phases, it is shown that the phase difference is the main contribution to the near-field polarization dependency. The experiments by using Talbot Scanning near-field optical microscopy apparatus prove it. This work is published on [Optics Communications, Vol. 281, 3254-3259 (2008)]. In addition, the femtosecond Talbot effect of high-density gratings is demonstrated. It is shown that the image contrast decreases for a longer detection distance and a shorter pulse. Beyond a critical distance, the image contrast will not change any more. The critical distance is related to the pulse width. This work is published by [Optics Communications, Vol. 281, 3230-3236 (2008)]. This dissertation includes my main research on simplified modal method for grating beam splitters, grating pair compressors and the Talbot effect of high-density gratings. It will enhance our knowledge on the grating diffraction process for practical applications, and improve the applications. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15286]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 郑将军. 光栅简化模式方法及应用[D]. 中国科学院上海光学精密机械研究所. 2009. |
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