| 题名 | 若干亚波长光栅的设计与应用 |
| 作者 | 吴俊 |
| 学位类别 | 博士 |
| 答辩日期 | 2013 |
| 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 | 亚波长光栅 傅里叶模态法 简化模式方法 分束器 增强吸收 |
| 其他题名 | Design and Applications of Some Subwavelength Gratings |
| 中文摘要 | 光栅作为最基本的一种周期性微纳结构，已经被广泛地研究和应用。目前，随着微纳加工技术和数值模拟技术的不断进步，对光栅的研究已经发展到一个新的高度，它脱离了单个器件的研究范畴，而逐渐与其它器件相结合，形成了许多新颖的光学器件。本论文针对目前快速发展的亚波长光栅方向，主要讨论了以下几个方面的研究工作： 1）基于双脊融石英光栅的分束器的设计与分析。针对800nm的波长，设计了TE偏振光垂直入射时的双脊融石英光栅1×5和1×7分束器。这两个分束光栅的平均衍射效率高于95%，一致性优于2%，衍射效率比传统的达曼光栅高了近15%。同时利用简化模式方法来定性解释所设计分束器衍射的物理本质。首先我们理论推导了双脊光栅的模式本征方程，并计算了1×5和1×7分束器的本征模。然后，计算了分束器的重叠积分和模式传播常数，通过对它们的分析，我们发现，仅仅有一些光栅模和衍射级次参与能量交换，因而通过少数几个光栅模，就可以分析衍射的物理本质。简化模式方法给出了垂直入射时分束器衍射的物理图像，对今后发展基于双脊光栅的器件有一定的指导意义。 2）导模谐振光栅的简化模式分析。提出了用于解释非对称覆盖的导模谐振光栅的简化模式分析，我们发现，它的谐振是由于光栅区域内的两个纵向光栅传播模的相互作用所引起。首先，比较了模式方法与傅里叶模态法的反射光谱和电场分布，并分析了高阶倏逝模对谐振峰的影响，发现简化模式方法和傅里叶模态法得出的结果符合地很好，这也证实了所提出方法的有效性。其次，基于所提出的简化模式方法，提出了矩阵Fabry-Perot谐振条件，用于估算谐振波长，并在最后提出并验证了Fabry-Perot谐振相位条件。所提出的简化模式方法，给出了导模谐振光栅谐振的物理本质，为后续解释复杂结构的谐振光栅的谐振现象有一定的指导意义。 3）薄膜非晶硅太阳能电池的增强吸收现象。从理论上研究了基于导模谐振效应的薄膜非晶硅太阳能电池的增强吸收现象，它是通过将一个单脊光栅或双脊光栅加上波导层作为太阳能电池的吸收层来实现。这两种结构的太阳能电池的平均积分吸收效率均有很好的角度无关性，一般来说，基于双脊光栅的太阳能电池比基于单脊光栅的有更好的光学性能。接着，我们定性地分析了基于导模谐振效应和双脊光栅结构的增强吸收的物理本质。为了进一步的减小反射和增加吸收，我们详细地探讨了减反光栅结构在太阳能电池中的应用。当加入减反光栅结构后，太阳能电池的平均积分吸收效率有着更大的角度无关性，远远优于无减反光栅结构和平板非晶硅薄膜加减反光栅结构的太阳能电池。所设计的基于单脊光栅或双脊光栅的太阳能电池，有着较小的吸收层厚度和高的积分吸收效率并且大的角度无关性，可以广泛应用于薄膜光伏、光探测器和红外成像等领域。所利用的融合了GMR效应、双脊光栅结构和减反光栅结构的设计理念可以用于指导新型的光栅基器件的设计。 4）金属光栅基器件的吸收效应。研究了金属光栅基器件的吸收效应，主要设计并分析了三种可见光波段的选择性吸收器：TE偏振选择性吸收器、TM偏振选择性吸收器和偏振无关选择性吸收器，所设计的吸收器在谐振波长处均可以实现近100%的完美吸收。通过分析吸收器的场分布和能量损失密度来定性分析完美吸收效应的内在物理本质，TE偏振吸收器的增强吸收主要是由于混合的腔模和导模谐振所致，而TM偏振吸收器的增强吸收是由于表面等离子体谐振所引起。最后，探讨了吸收光谱和光栅结构参数的关系，这可以用于指导偏振相关和无关的光栅基选择性吸收器的设计。所设计的吸收器可以用于高质量的探测器，热辐射器和传感器。 本文拓展了简化模式方法在双脊光栅和高对比度光栅领域的应用，设计了基于双脊光栅的分束器，探讨了基于光栅结构的增强吸收效应，它们将有益于亚波长光栅的进一步发展和应用。未来，对于亚波长光栅的研究还会继续深化。 |
| 英文摘要 | A grating is the most basic periodic micro-nano structure, which has been widely studied and used for various applications. At present, as the fabrication and numerical simulation techniques have been highly developed, the research on gratings has grown to a new level: it is no longer developed as a single device, but is combined with other devices to form a number of novel optical devices. Design and applications of subwavelength gratings are presented in this doctoral dissertation: 1) The design and analysis of beam splitters based on double-groove fused-silica gratings. Double-groove fused-silica gratings for 1×5 and 1×7 TE-polarization beam splitting under normal incidence at the wavelength of 800nm are studied. The average diffraction efficiencies of the two gratings are both more than 95% with uniformity better than 2%. The diffraction efficiencies of these gratings are approximate 15% more than the conventional Dammann gratings. Physical understanding of the diffraction behaviors taking place inside the beam splitting gratings is presented by the modal method. The mode eigenvalue equation of the double-groove grating is derived theoretically. The eigen-modes of 1×5 and 1×7 TE-polarization beam splitting gratings are obtained from the eigenvalue equation. Then, we calculate the overlap integral and modal propagation constants. It is found that only a few grating modes and diffraction orders participate in the energy exchange, so we can give the physical explanation by use of a few grating modes. The proposed method of analysing beam splitters under normal incidence should be helpful for developing new double-groove grating-based devices. 2) A simplified modal method to explain the resonance phenomenon of guided mode resonance (GMR) gratings with asymmetric coatings is presented. The resonance is due to the interaction of two grating propagation modes inside the grating. The reflectivity spectrums and electric field distributions calculated from simplified modal method are compared with those from the Fourier modal method. The influences of high-order evanescent modes to the resonance peak are analyzed. The agreement between the simplified modal method and the Fourier modal method is very well, which confirms the proposed method. A matrix Fabry-Perot (FP) resonance condition is developed to evaluate the resonance wavelength. An explanation for the resonance phenomenon based on the FP resonance phase condition is also proposed and demonstrated. The simplified method gives a clear physical insight of GMR gratings, which should be useful for analysis of a variety of other resonance gratings. 3) The enhancement of absorption in a thin-film amorphous silicon solar cell based on guided mode resonance is theoretically investigated. This is achieved by patterning a single-groove or a double-groove grating with waveguide layer as the absorbing layer. The averaged integrated absorptions are weakly dependent on the angle of incidence in both grating structures. It is shown the optimized solar cell with double-groove grating has better optical performance than single-groove grating structures. The qualitative understanding of enhanced absorption based on guided mode resonance and double-groove grating structure is presented. The antireflective grating structures are proposed and discussed for reducing reflection and enhancing absorption. The grating with antireflective layer is less dependent on the angle of incidence, which is much better than the performance of gratings without an antireflective grating and the planar a-Si film with an anti-reflection grating. The designed solar cell based on single- and double-groove grating structures with small thicknesses of absorbing layer have high integrated absorption and weakly dependent on incident angle, which should be useful for applications in film photovoltaics, photodetectors and infrared imaging. The design philosophy, which blends GMR effects、double-groove grating structure and antireflective grating structure, can be used to design other new grating-based devices. 4) The absorption effect in metallic-grating-based devices is theoretically investigated. Three kinds of spectrum selective absorbers (TE polarization, TM polarization and polarization-independent) exhibiting near-unity absorption at the resonant wavelength are studied at visible frequencies. The underlying physics understanding of such perfect absorption effects is illustrated by investigating the field distributions and power loss density in these absorbers. The enhancement of absorption is attributed to the hybridization of cavity mode and guide mode resonance for TE polarization absorber, and attributed to the surface plasmon resonance for TM polarization absorber with ultra-thin grating-spacer structure. The relationship between the absorption spectrum and the geometric parameters of the structures is studied, which can be useful for designing a polarization-dependent or -independent selective absorber based on a grating structure in the visible region. The designed absorber can be used in high quality detectors, thermal emitters and sensors. This dissertation extends the applications of simplified modal method to the area of double-groove gratings and high-contrast gratings. A beam splitter based on double-groove grating is designed and analysized. The enhanced absorption effects of the devices based on grating structures are studied. All of them will benefit the further development and application of subewalength gratings. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15747]  |
| 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 | 吴俊. 若干亚波长光栅的设计与应用[D]. 中国科学院上海光学精密机械研究所. 2013. |
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