Research On Novel SOI Grating Coulper In Optiacl Communication Systems

With the rapid development of optical communication, the application of coupling devices in optical communication system is so extensive that the research of high performance coupling devices is very important. The material of coupling devices in integrated optics is Silicon-on-Insulator(SOI) structure in common, thus there is a layer of Silica between the Silicon waveguide layer on the top and the substrate on the bottom. The relatively high refractive index of SOI leads to high efficient transmission characteristic.The most valid factors of coupling devices are high coupling efficiency and broad bandwidth. The SOI based grating couplers become the hot point in this study because of the advantages above. However, the un-vertical coupling made by the oblique incidence of the fiber has influenced the testing and integrated application to a great intend, so the study of the perfectly-vertical coupling of the grating coupler is brought into being. The breakthrough of this coupling process has broadened the integrated application and development of the grating coupler in optical communication system widely.In this dissertation , the research is focusing on the coupling characteristic of grating coupler based on SOI and its applications in optical communication system. The main research results and innovations are as follows:1. The methods for sub-wavelength grating coupling have been studied - Rigorous Coupled Wave Analysis (RCWA) and the Bragg conditions. Besides, the Finite Element Method (FEM) for simulation of the grating coupler is studied. We learned the core ideas of FEM and discussed the boundary conditions and the mesh size in element simulation.2. The design of periodic grating coupler in SOI has been accomplished. In condition of the given grating waveguide layer's thickness,we have calculated and optimized the parameters which results to coupling efficiency up to 80% at 1550nm in simulation.3. The slanted SOI grating coupler for vertical coupling has been proposed. The method to optimize the grating structure and achieve the specified vertical coupling is introduced. The numerical simulations shows that the novel grating coupler can offer the coupling efficiency as high as 88.6% at 1550nm TE mode, as well as a broad 1dB bandwidth of 40nm.4. The binary blazed grating coupler in SOI for vertical coupling has been designed and accomplished. Based on the Equivalent Medium theory,including the first order approximation method based on the form of double refraction theory and the more accurate high-order approximation model,we have designed the binary blazed grating coupler for vertical coupling with a given thickness of grating waveguide layer 340 nm, the result of the coupling efficiency is up to 65% at 1550nm.5. The fabrication of the 1D periodic grating coupler with the period 630nm in SOI chip and the reflective sub-wavelength focusing grating with the focal length of 400?m has been accomplished properly. Besides, we have also built the testing system of reflective sub-wavelength grating with focusing ability. According to the testing data, the reflective index of the reflective focusing grating is 80.4%. The error between the experimental result and the numerical simulation is analyzed.