Study On Waveguide Grating Coupler Based On Silicon Substrate

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.