||With demand for huge bandwidth, fast connections and varieties of services, Dense Wavelength Division Multiplexing (DWDM) network is such a qualified next generation network infrastructure. As core switching nodes, optical switches have raised a lot of research challenges. Compared to its electronic counterpart, though similar in concept, its implementation approach has a great difference especially when involved in optical buffer implementation to resolve contentions. Due to no optical Random Access Memory (RAM) available, fiber is usually used to emulate buffering effect by introducing an additional period of propagation delay. This approach combined with appropriate placement of tunable wavelength converters can achieve impressive buffering effect for an optical switching system. In thesis, we propose two multistage systems, one is serially cascaded one and the other is fully-connected one. Both of them can maintain incoming packets "First In First Out" (FIFO) order. But in the serially cascaded system, it intends to determine a complete available internal route for packets before they are admitted into system; while in fully-connected system, it determines internal path for packets section by section and has more flexibility in path selection due to its local-resource-focused. simulation studies show quite impressive performances for these two systems. Further the later one's potential in provision of differentiated switching under Differentiated Service framework is also indicated and a simple differentiated switching algorithm is proposed and evaluated under simplified two classes of heterogeneous traffic scenario. This thesis is organized as five parts: the lst part introduces DWDM network and the function modules of optical packet switch. The 2nd part introduces current optical components technology, namely AWG and wavelength converters, presents two typical optical packet switches examples in literature. The 3rd part introduces our serially cascaded optical switch system. The 4th part introduces our fully-connected optical switch system. Its potentials to provide differentiated switching simultaneously is also explained. Finally the 5th part concludes the thesis.