Modelling, design, and simulation of facet reflection and gain polarization dependence in semiconductor optical amplifiers

The growing interest in semiconductor optical amplifiers (SOAs) is related to the development of metropolitan optical networks where the SOA, as a linear amplifier, is a cost-effective alternative to the erbium-doped fibre amplifier (EDFA), and to the development of all-optical networks, where the SOA, because of its non-linear properties and fast gain dynamics, serves as a basis for various all-optical processing components. Yet, some of its characteristics are inferior to those of EDFA, and a significant research effort. has been undertaken to reduce the gap between them. Two deficiencies of SOAs are addressed in this thesis: polarization-dependent gain (PDG) and facet reflection.; The problem of PDG in SOAs with an unstrained bulk active region has been reduced to designing a waveguide structure with equal quasi-transverse electric (QTE) and quasi-transverse-magnetic (QTM) optical confinement. Such a design, a novel ridge waveguide with horizontal asymmetry, is proposed. The horizontal asymmetry, a new degree of control over the confinement factors, relaxes stringent constraints formerly imposed on material compositions (e.g., refractive indices) and geometrical dimensions in an attempt to reach low polarization sensitivity over a broad wavelength operating range. The tolerance analysis with respect to the key parameters is presented. The problem is then studied by using a more accurate model, where such effects as non-uniform interband loss, carrier-induced index change, index wavelength dependence, and carrier diffusion are taken into account.; The facet reflection in SOAs and some other devices, such as superluminescent light emitting diodes (SLEDS), must be minimized in order to decrease the Fabry-Perot modulations of the gain spectrum. Therefore, precise evaluation of facet reflection is highly desirable in the design and simulation of these devices. In this study, the three-dimensional (3D) finite-difference time-domain (FDTD) method was implemented on a parallel computing algorithm for the calculation of facet. reflection in optical waveguides. The FDTD provides the versatility necessary for simulating devices with a complex structure. The parallelization of the algorithm eliminates the constraint on the size of the structure that is usually associated with the FDTD method. 3D FDTD is used to show that even a subtle difference in the waveguide ridge shape has significant impact on modal reflectivity.