Study Of Silicon-based Micro-Nano Binary Blazed Grating Vertical Coupler

Recently, silicon-based optical interconnection as well as optical computing becomes the research hotspots in the world, especially for the research on both passive and active optoelectronic devices which are based on SOI wafer. And now, a lot of passive optoelectronic devices have been produced on SOI wafer, such as optical waveguides, modulators, filters, WDM devices, etc. However, silicon-based on-chip light source is very difficult to be realized, so the external light source is still the main choice. The high coupling efficiency between external source and SOI waveguide becomes the key issue. Vertical grating couplers have the advantage of high coupling efficiency and good alignment tolerance.Supported by the"Creative Foundation of Wuhan National Laboratory for Opto -electronics", the design and fabrication of binary blazed vertical grating coupler has been studied in this thesis. The main works are listed as follows:(1) Based on the rigorous coupled-wave analysis, the coupling efficiencies of ordinary grating coupler and binary blazed grating coupler have been deduced and compared.(2) The theoretical design of binary blazed grating coupler based on SOI have been introduced in detail. Simulations demonstrate it has higher coupling efficiency and larger bandwidth under nearly vertical coupling. When the blazed grating is shallowly etched, the coupling efficiency can reach as high as 60% without introducing any extra back reflection mirror in the substrate.(3) Based on the grating diffraction and effective medium approximation, a novel blazed grating coupler consisting of two dimensional (2D) fully-etched rectangular air holes is proposed to enhance the coupling efficiency and bandwidth for vertical coupling between fiber and silicon-on-insulator (SOI) waveguide. 2D finite-difference time-domain (FDTD) simulations demonstrate that the coupling efficiency at 1550 nm wavelength is 60.2%, and the 1dB bandwidth is 100 nm. The proposed grating coupler along with the waveguide can be fabricated by only one step of lithography and etching processes, without any overlay processes. (4) The fabrication process of binary blazed vertical grating coupler have been studied, and the initial device sample has been produced.