(This thesis consists of two parts.) Part I Comparison of Traveling Wave and Gain-Clamped Semiconductor Optical Amplifiers. Today's Wavelength Division Multiplexing (WDM) optical networks are getting dynamic light-path reconfigurable and optical transparent. Optical amplification without optoelectronic conversion is a key technology in all-optical networks. semiconductor optical amplifier (SOA) is a very potential device in this field. Besides the linear amplification, the nonlinear features of SOA make it has a broad application in wavelength conversion, tunable wavelength filter, optical switching and optical logic. The simple structure and very compact size of SOA indicate the essential low-cost and compatibility of integration. Resonant cavity is the basic structure of conventional SOAs, while gain-clamped SOAs (GC-SOAs) provide a constant gain which raises a lot of interests in applications. SOA with Distributed Bragg Reflectors (DBR) is one of the structures to realize the clamped gain. In this thesis the performances of traveling wave SOA (TW-SOA) and DBR-SOA are compared through a dynamic model. This model consists of a distributed feedback wave equation, a carrier rate equation and a material gain model, thereby can be used to simulate both of the two SOAs. To balance the time cost of simulation and the accuracy of the result, three important non-physical parameters, simulated bandwidth, cavity discritization and frequency discretizaiton, are investigated. The simulation results show that DBR-SOA has a very stable device gain which is independent on input optical power. From a noise level point of view DBR-SOA and TW-SOA have different characteristics. These comparison is conducted with both large signal input and small signal input. In addition, a desirable application, SOA in a multi-channel WDM system, is also simulated with GC-SOA and TW-SOA. The Bit Error Rate (BER) of TW-SOA increases greatly due to inter-channel cross talk, while the BER of GC-SOA is virtually constant with the variation of WDM channel number. Another application, wavelength converter, shows TW-SOA is very useful in non-linear application. Part II Impact of Dispersion on Hybrid of Frequency-Hopped Optical CDMA and WDMA Networks. A new analytical formula for analysis of the system performance of the Hybrid of Wavelength Division Multiple Access (WDMA) and Code Division Multiple Access (CDMA) is developed and presented. The effects of fiber dispersion and inter-channel crosstalk are considered and their impact on system performance is analyzed in terms of power penalty. Finally, methods to overcome the effects of the fiber dispersion are discussed. / Thesis / Master of Applied Science (MASc)