In OTDM system, high bit rate is achieved on a single wavelength by bitinterleaving a number of optical signals with lower bit rate (base data rate). The gating times needed in the demultiplexer are in the order of picoseconds, which cannot be realized with electrical gates. Therefore, employing all- optical signal processing in the demultiplexer is essential to enhance the switching speed. This work investigates in details the performance of all- optical interferometric gates based on semiconductor optical amplifier (SOA). The objective is to realize all _ optical gate in OTDM demultiplexers for high bit rate transmission (above 500Gb/s). The switching effect in the SOA is achieved via cross _phase modulation between the signal and the control pulse. The ultrafast femtosecond gain and phase dynamics of SOA are investigated in details. A comprehensive model is developed which takes into account interband transition, intraband transition, spectral hole burning (SHB), carrier heating (CH), and two-photon absorption (TPA)) and polarization states of the control pulse and data. The model is used to extract the femtosecond switching dynamics of the SOA under different operating conditions. Two types of SOA-based optical gates are investigated in this work, Mach-Zehnder Interferometer (MZI) and Ultrafast Nonlinear interferometer (UNI). The gates are characterized by switching window calculation. The switching windows are evaluated using different criteria such as switching width and on-off contrast ratio to compare the performance of the gates when they are used in the OTDM demultiplexing systems. The results indicate clearly that, with a suitable parameters control, a switching window width of . 2ps and on-off contrast ratio below -11 dB can be achieved. The performance of the most promising gates are investigated for demultiplexing application using the integrated contrast ratio (ICR). Simulation results are presented for OTDM bit rates up to 560 Gb/s and base data rate of 10Gb/s and 40Gb/s. Some of the results predicated in this work are compared with experimental data reported in the literature.