摘要
硅基波导光栅耦合器件在集成光学发展中扮演着重要角色,由于其具有多功能性、高效率、低功耗、工艺简单等优点而受到国内外研究人员的广泛关注。目前,对波导光栅耦合器件的理论分析、结构优化设计、制备方法、以及材料选择等方面还有大量的研究工作要做。
本文在“国家自然科学基金”和“国防科技大学校预研基金”的支持下,研究了硅基波导光栅耦合器件的基本原理,利用严格耦合波理论和FDTD数值模拟方法对器件结构进行设计,探讨了器件的制备工艺和过程,并利用电子束光刻和感应耦合等离子体刻蚀技术对器件进行了加工制作。
本文通过对硅基波导光栅耦合器件理论和实验的研究,主要取得了一下创新性成果:
(1)设计了一种应用于波导与波导之间耦合的微型多阶梯式光栅耦合器,这种耦合器以SOI材料结构为基础,并且具有超长带宽和极小的尺寸(光栅长度仅为3微米)。入射光源限定为TE偏振光且垂直入射。模拟结果表明这种耦合器具有160nm的3dB带宽(1390nm-1550nm),耦合器入射光源波长为1550nm附近时耦合效率50%左右。同时在入射波长为1460nm时耦合器的耦合效率能达到67.5%。
(2)提出了一种采用全刻蚀结构的高效率近垂直耦合的二元光栅耦合器,该种耦合器的制备与CMOS工艺兼容,可以利用一步套刻制作而成,并可与其他SOI器件集成。当入射波波长分别为1550nm和1563nm时,由光纤经过该耦合器耦合进入波导的耦合效率分别为59.2%和76.9%,并且还具33nm的3dB带宽。同时模拟结果也表明该结构具有19nm的刻蚀深度容差和6.5°的入射角度容差。
(3)以全刻蚀二元闪耀光栅耦合器为基础,设计了一种对称式全刻蚀啁啾型亚波长二元闪耀光栅分束器,该分束器可以对TE模入射光实现均匀分束,当波长为1580nm的TE模光源垂直入射时,分束器水平两端的耦合效率能够分别达到43.627%和43.753%。并且该结构具有20nm的刻蚀高度容差和3°的入射角度容差,便于加工和集成。
(4)搭建了耦合器件的测试平台。利用电子束光刻和感应耦合等离子体刻蚀技术制备了全刻蚀二元闪耀光栅耦合器和普通光栅耦合器,并对其进行了器件性能的测试,获得了一些初步的实验结果。
Waveguide grating coupler based on silicon substrate has been playing an important role in the development of integrated optics, which attracts more and more attentions. Waveguide grating coupler has many advantages over their competitors, such as versatility, high efficiency, low power consumption and simple technology. There remains lots of work to do in the research of waveguide grating coupler, such as theoretical analysis, structural optimization design, fabrication methods and material selection.
Supported by the“National Natural Science Foundation of China”and the“Foundation of National University of Defense Technology”, the basic principles of the waveguide grating coupler based on silicon substrate is studied in this thesis, device structures is are designed with the rigorous coupled wave analysis and the FDTD simulation method, the preparation procedure and fabrication process are investigated, some devices are fabricated by Electron Beam Lithography (EBL) and Inductively Coupled Plasma (ICP) etching, and the coupling efficiency of the waveguide grating coupler is measured and analyzed by the fiber-to-waveguide coupling testing platform.
A number of achievements were obtained through the theoretical and experimental study of the grating coupler:
(1) A compact multilevel grating coupler based on SOI material structure is proposed to realize coupling between waveguide and waveguide, which has the ultrabroad bandwidth and extremely compact dimension (with the grating length of 3μm). The incident wave is TE polarization and designed as normal incidence. The simulation results indicate that the 3dB bandwidth of 160nm from 1390nm to 1550nm can be obtained, accompanied by the coupling efficiency of approximately 50% around 1550nm. Simultaneously, the sufficient high coupling efficiency of 67.5% at the wavelength of 1460nm has also been observed.
(2) A high-efficiency binary blazed grating nearly vertical coupler with fully-etched spacings is proposed, which is compatible with the CMOS technologies and can be fabricated in one lithography step integrated with other SOI components. For TE polarized incident light, the coupling efficiencies from a fiber to waveguide are 59.2% at the wavelength of 1550nm and 76.9% at 1563nm, respectively. A 3 dB bandwidth of 33nm is also obtained. The numerical simulation also shows that the tolerances of 19nm in etched depth and 6.5o in incident angle are achievable.
(3) A novel syminetrical chirped grating beam splitter based on binary blazed grating is proposed, which with fully-etched grating structure. This structure can realize equal-power splitting operation under the condition of TE polarization incidence. While under the condition of absolutely normal incidence, the coupling efficiency of the left and the right branches is 43.627% and 43.753% at the wavelength of 1580nm. Moreover, this structure has tolerances of 20nm in etched depth and 3o in incident angle, which brings convenience to manufacture facility.
(4) The coupling testing platform is constructed. The fully-etched binary blazed grating coupler and a normal grating coupler are fabricated by Electron Beam Lithography (EBL) and Inductively Coupled Plasma (ICP) etching, and the preliminary test results are obtained by testing the performance of the devices.
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