Compact SOI Grating Coupler And The Fabrication Technology

With the rapid development of integrated optics and silicon photonics, the grating attracts more and more attentions because some novel characters arise when the device dimension goes down to subwavelength. One of the applications is using it as a coupler for nano-waveguides. Compared with other nanophotonic coupling strategies, grating coupling owns higher coupling efficiency, enables wafer-scale testing of the integrated circuits and holds the promise of low-cost packaging, etc. All these advantages make it the most promising method for the integrated optical circuits.Supported by the "National Basic Research Program of China" and "Natural Science Foundation of Hubei Province", the design, fabrication and application of the grating coupler are systematically studied in this thesis, and a series of nanophotonic devices are fabricated and estimated.A number of novel achievements were obtained through the theoretical and experimental study of the grating coupler:(1)A novel binary blazed grating coupler was theoretically designed and demonstrated. Compared with other grating coupler, it can realize high coupling efficiency and relatively broad bandwidth under the condition of perfectly vertical coupling. Moreover, the fabrication technology is compatible with conventional CMOS technology and satisfies the demand of Planar Lightwave Circuit (PLC) technology, which makes it possible for mass production.(2)A novel polarization beam splitter using a two-layer grating coupler is proposed and demonstrated. It can directly couple the normally incident light from fiber into two separate waveguides according to their polarization states while splitting them. It realizes high coupling efficiency and a good extinction ratio by using the unique polarization property of binary blazed grating couplers. The coupling length is less than 14μm.The extinction ratio is better than 20dB for both polarizations over a 40nm wavelength range, and the coupling efficiencies for the two layers are 58% and 50%. It provides an effective polarization diversity approach for the problem of fiber to naowaveguide coupling.(3)With the optimization of processes, a high-density nonuniform subwavelength grating coupler was fabricated by Electron Beam Lithography (EBL) and Inductively Coupled Plasma (ICP) etching. The smallest linewidth and spacing are only 30nm.(4)The fabrication process of annular photonic crystals (APC) on silicon-on-insulator (SOI) wafers is addressed for the first time. A self-alignment procedure for nanofabrication using atomic layer deposition (ALD) and sacrificial etching is established to place accurately nanosized dielectric rods in nanosized circular air holes. Avoiding the challenging EBL alignment, this method achieves atomic level precision and shows high stability. A number of processes in nanofabrication technology were studied, like different prebake and development conditions in EBL, proximity effect correction methods, and sidewall roughness reduction method, which are valuable for the fabrication of nanodevices.