| 题名 | 高密度深刻蚀石英光栅分束器的研究 |
| 作者 | 王博 |
| 学位类别 | 博士 |
| 答辩日期 | 2008 |
| 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 | 微光学 全息 感应耦合等离子体 熔融石英 偏振分束光栅 分束器 |
| 其他题名 | The study on beam splitters of high-density deep-etched fused-silica gratings |
| 中文摘要 | 高密度深刻蚀光栅表现出了有用的光学功能，例如偏振分束和1×2分束。这里，高密度表示周期具有波长量级或者亚波长量级，深刻蚀表示深度达到波长量级或者几个波长量级。基于高密度深刻蚀光栅，能够设计新型的微光学元件。偏振分束器和1×2分束器是两种常用的光学元件，偏振分束器能够将两种偏振态相互垂直的光束分为不同的传播方向，1×2分束器能够把一束入射光分成两束能量相等的出射光。与其它普通光学元件相比，高密度深刻蚀光栅微光学元件结构紧凑，易于小型化和集成化，并且插入损耗小，是一种无热器件。尤其是深刻蚀熔融石英光栅，损伤阈值很高，热膨胀系数小，这些特性使得它们能够适用于高强度激光系统中。本论文探讨了高密度熔融石英光栅的深刻蚀技术，通过严格耦合波分析矢量衍射理论优化设计了具有高效率的高密度深刻蚀石英光栅偏振分束器和宽带1×2分束器，并利用全息记录和感应耦合等离子体干法刻蚀技术给出制作实例，基于模式方法，对于高密度深刻蚀透射光栅给予物理机制解释。 高密度光栅具有新颖的衍射效应，深刻蚀或者大面积的高密度光栅是有用的光学元件。描述了高密度深刻蚀熔融石英光栅的详细制作过程，包括掩模版的制作工艺。利用全息记录和感应耦合等离子体干法刻蚀技术制作了高密度深刻蚀熔融石英光栅。从扫描电子显微镜图像可以看出，所制作的光栅周期为890 nm、深度达到3.6 微米，具有高深宽比8.09；并且得到面积为55×55 平方毫米高密度熔融石英光栅，周期为400 nm，光栅表面均匀。实验证明感应耦合等离子体技术是一种有效的制造新型熔融石英光栅微光学元件的干法刻蚀方法。 偏振分束器是一种常用的光学元件。描述了高密度深刻蚀石英偏振分束光栅及其物理机制解释。针对常用激光波长351、441.6、532、632.8、800、1053和1550 nm，为了获得高消光比和高衍射效率，利用严格耦合波分析数值计算优化了光栅周期和深度。这些数值结果和物理解释有助于设计和制造高消光比和高衍射效率偏振分束光栅。利用全息记录和感应耦合等离子体刻蚀技术制作了石英偏振分束光栅。在1550 nm波长处，对于TE偏振光，-1级的实验衍射效率接近于80%；对于TM偏振光，0级的实验衍射效率大于85%。对于TE/TM偏振光，此透射偏振分束光栅的物理机制能用模式方法中的有效折射率来解释。如果入射光在光栅区域所激发的两个模式在光栅基底的相位差满足pi的偶数倍或者奇数倍，那么光栅在0或者-1级高效率衍射，这种解释是模式方法的一个有用的延伸。 常用的基于多层介质膜的宽带分束器也是非常有用的光学元件。我们描述了利用二元熔融石英相位光栅实现透射宽带1×2分束器。为了针对1550 nm波长在0和-1级获得高衍射效率和均匀度，利用严格耦合波分析优化设计了光栅轮廓参数。通过全息记录和感应耦合等离子体干法刻蚀技术，制作了该熔融石英分束光栅。在利特罗入射下，测量的衍射到两个级次的效率为(45%×2) = 90%。这种宽带1×2分束光栅的物理机制可以利用模式方法，基于入射光所激发的两个模式的双光束干涉进行很好的解释，即在光栅基底界面的相位差满足pi/2。这种宽带光谱下的高效率是不能用标量光栅理论来解释的。 熔融石英具有高光学质量，是一种理想的光学材料，损伤阈值非常高。更重要的是，它具有从深紫外到远红外的宽透射谱。由于结构紧凑、制作过程简单并且易于大量生产，所设计和制作的高密度深刻蚀石英光栅分束器是光通信和光学信息处理系统中有用的器件。 |
| 英文摘要 | High-density deep-etched gratings demonstrate useful optical functions, such as polarizing beam splitting and two-port beam splitting. Here the high density means the period is near to the wavelength or subwavelength, and the deep etched means the depth is near the wavelength or several wavelengths. Based on high-density deep-etched gratings, many novel micro-optical elements can be designed. Polarizing beam splitters (PBSs) and two-port beam splitters are widely used optical devices. PBSs can separate two orthogonally polarized wave beams into different propagation directions, and two-port beam splitters can separate an input beam into two beams with equal intensity. Comparing with other ordinary optical elements, compact sizes of micro-optical elements based on high-density deep-etched gratings are advantageous to the miniaturization and integration. Moreover, they are athermal devices with low insertion losses. Especially, deep-etched fused-silica gratings have high damage thresholds and low coefficients of thermal expansion. These properties make them very suitable for high intensity laser systems. In this paper, we investigated the deep etching technology of high-density fused-silica gratings. PBSs and wideband two-port beam splitters of high-density deep-etched fused-silica gratings were optimized with high efficiency using the vector diffraction theory of the rigorous coupled-wave analysis (RCWA). Fabrication examples were given by holography recording and inductively coupled plasma (ICP) dry etching techiniques. Based on the modal method, physical mechianisms were explained for the high-density deep-etched transmission gratings. High-density gratings have novel diffraction properties. In practice, deep-etched or large area high-density gratings should be useful. We described the detailed fabrication process of high-density deep-etched fused-silica gratings including formation techniques of grating masks, which can be fabricated using holographic recording and ICP dry etching techniques. A deep-etched fused-silica grating was obtained with period 890 nm and depth 3.6 micrometers, whose aspect ratio can reach 8.09 from the experimental scanning electron micrograph. Moreover, a high-density fused-silica grating was achieved with period 400 nm and area 55×55 mm2 homogeneously. It demonstrates that the ICP technique is an effective dry etching method for fabrication of fused-silica gratings as novel micro-optical elements. PBS is a widely used optical element. We described high-density deep-etched fused-silica PBS and their physical mechanism explanation. Optimized numerical results of the grating period and depth were given using the RCWA in order to achieve high extinction ratio and diffraction efficiency for the usual laser wavelengths 351, 441.6, 532, 632.8, 800, 1053, and 1550 nm. These numerical results and simple physical explanation provide a useful guideline for design and fabrication of a PBS grating with high extinction ratio and diffraction efficiency. Holographic recording and ICP etching techniques were employed to fabricate the fused-silica PBS grating. Experimental results of diffraction efficiencies approaching 80% for TE-polarized wave in the -1st order and more than 85% for TM-polarized wave in the 0th order were obtained at a wavelength of 1550 nm. The physical mechanism of such a PBS grating can be well explained based on the modal method with the effective indices of the modes for TE/TM polarization. The grating is efficient in the 0th or -1st orders, respectively, if the phase difference between the two modes excited by the incident wave meets an even- or odd-numbered multiple of pi at the grating-substrate interface, which is useful extension of the modal method. The usual beam splitter of the multilayer coated film with a wideband spectrum is also a useful optical element. We described the realization of a transmission wideband two-port beam splitter based on a binary fused-silica phase grating. To achieve high efficiency and equality in the diffracted 0th and -1st orders, the grating profile parameters were optimized using the RCWA at a wavelength of 1550 nm. Holographic recording and ICP dry etching technique were used to fabricate the fused-silica beam splitter grating. The measured efficiency of (45%×2) = 90% diffracted into the both orders can be obtained with the fabricated grating under Littrow mounting. The physical mechanism of such a wideband two-port beam splitter grating can be well explained by the modal method based on a two-beam interference of the modes excited by the incident wave, where the phase difference should be pi/2 at the grating-substrate interface. The high efficiency with a wideband spectrum can not be explained using the scalar grating theory. The fused silica is an ideal optical material with high optical quality which can stand with a high laser damage threshold. More importantly, it has a wide transmitting spectrum ranging from deep ultraviolet to far infrared. Because of compact structure and simple fabrication process suitable for mass reproduction, the designed and fabricated beam splitters of high-density deep-etched fused-silica gratings are useful elements in optical communication and optical information processing system. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15213]  |
| 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 | 王博. 高密度深刻蚀石英光栅分束器的研究[D]. 中国科学院上海光学精密机械研究所. 2008. |
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