Modeling, Design And Fabrication Of Arrayed-waveguide Gratings

As a typical integrated optical device, an arrayed-waveguide grating (AWG) has excellent performances and broad applications in e.g. optical communication systems. In this thesis, novel simulation modelings and optimal designs for AWGs are presented. The designed AWGs are also fabricated and characterized.Numerical simulation plays a very important role for estimating and optimizing the performances of an optical waveguide device before its fabrication. Therefore, effective and reliable simulation tools are desirable for the design of integrated optical waveguide devices. In this thesis, the general theory of optical waveguides is reviewed first. Analytical and numerical methods for analyzing optical waveguides are summarized. A general formula is derived for a finite-difference method (FDM) with non-uniform grids in a cylindrical coordinate system, and a perfectly matched layer (PML) is used for the boundary treatment. Based on this general formula, one can easily obtain the formulas of an FDM for several other special cases (e.g., an FDM with uniform grids, an FDM in an orthogonal coordinate system, etc). A beam propagation method (BPM), which is a powerful and popular tool for simulating the light propagation in an integrated optical device, is also reviewed and improved. A two-dimensional (2D) paraxial BPM in a cylindrical coordinate system is extended to a wide-angle BPM. With these numerical methods, the characteristics of some optical waveguides are analyzed. First, the constant c in the single mode condition for a silicon-on-insulator (SOI) rib waveguide with a large cross-section is determined by using an FDM. Secondly, the birefringence characteristic for an SOI rib waveguide is analyzed and the design for a non-birefringent SOI rib waveguide is given by normalizing the width and height of the rib. Thirdly, a multimode bent waveguide is appropriately designed so that the bending losses of the higher-order modes are very large and a low-loss singlemode propagation in a multimode bent waveguide is realized. This is useful for improving the integration density.Simulation medelings for an AWG demultiplexer are studied in this thesis. First, a simple method is given with a Gaussian approximation for the fundamental modal field of the waveguide in an AWG. To be more accurate, a simulation procedure based on a BPM in an orthogonal coordinate system is given by dividing an AWG into three regions (i.e., the first free propagation region (FPR), the arrayed waveguides, and the second FPR). In order to study the influences of the bending sections on the spectral response, the BPM in a cylindrical coordinate system is introduced and a global simulation for the output part of an AWGdemultiplexer is obtained. In this thesis a three-dimensional (3D) simulation method based or the Kirchhoff-Huygens diffraction formula is introduced. The 2D Kirchhoff-Huygens diffraction formula is used for the light propagation in the FPRs. From this 3D simulation method, a novel effective 2D model (which is more accurate than a conventional 2D model based on an effective index method) is developed. In order to improve the efficiency and accuracy of the AWG simulation, a novel 3D simulation method, which combines a 3D BPM and the 2D Kirchhoff-Huygens diffraction formula, is developed. In this method, a 3D BPM in a polar coordinate system is used to simulate the light propagation in the region containing the junction between the first FPR and the arrayed waveguides so that the coupling coefficients of each arrayed waveguide is calculated conveniently and accurately. In the region of the second FPR, a standard BPM is used for the simulation. In the regular BPM simulation, one only needs to include several arrayed waveguides in the computational domain due to the uniformly arrangement of the arrayed waveguides and thus the computation efficiency is improved. By using one (or several) of these methods, the performances of a designed AWG demultiplexer are estimated, (i) the influence of the fabrication errors on the spectral response of an AWG demu...