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Abstract

This thesis discusses several important applications of directional coupler-based and multimode interference coupler-based devices. The numerical analysis in this study has been carried out by using the powerful and versatile finite element method (FEM). This method has been proved to be the most accurate numerical methods to date for the analysis of optical waveguides. In this study the vector H-field formulation is used along with the penalty function term to eliminate the spurious solutions.

Using the finite element method the accurate propagation constants o f all the modes and the field profiles can be calculated. However, the finite element method cannot calculate the power transfer efficiency directly, hence the Least Squares Boundary Residual method (LSBR) is used with the FEM for this purpose. The LSBR method is rigorously convergent, satisfying the boundary conditions in the least squares sense over the discontinuity interface. The error minimisation in this approach is global rather than sampled as in the point matching method. Using this method the transmission coefficients of all the modes and the reflection coefficients of the fundamental mode can be determined once the transmission coefficients o f all the modes are calculated, and the power transfer from the input to the coupler section and at the output ports can be evaluated.

In this work, to show the advantages o f the finite element approach an optical polarizer with metal clad directional coupler has been designed and analyzed. The modal loss is also calculated for the TM polarised mode and a Multiple Quantum Well based optical polarizer with two-dimensional confinement is studied. Its equivalent index has been calculated by using the finite element and the results are compared with the analytical results. A large section of this thesis is devoted to the study of multimode interference based devices. An interesting and useful comparison is made on their operating properties such as the crosstalk, device length, polarization dependence and fabrication tolerance of the multimode and the directional coupler-based devices. Finally, the spot size expander approach for improved laser-to-fibre coupling is discussed. In this study initially a taper-based approach is discussed with the simulated values for the coupling loss and reflection coefficients, following which a novel approach using a synchronous directional coupler-based mode expander is studied. Some multiguide directional coupler-based spot size expanders are also discussed and finally a new approach using multimode interference-based compact devices is presented, which is technologically more promising, due to the fascinating properties o f the multimode based devices. This is an interesting exciting area in the field of photonic engineering.

This thesis, starting with a small introductory chapter on optical communication will take the reader in a step-by-step approach to understand the principles and properties of the optical devices that are important for the design of all optical systems. Most of the applications that are presented in this thesis are of great interest to the optical community and I hope the reader will enjoy the contents of this thesis.

Publication Type:	Thesis (Doctoral)
Subjects:	H Social Sciences > HE Transportation and Communications Q Science > QA Mathematics > QA75 Electronic computers. Computer science T Technology > T Technology (General)
Departments:	School of Science & Technology > Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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