Single mode SOI waveguide devices with low propagation loss and low insertion loss have been demonstrated at wavelength λ=1.3μm and 1.55μm, respectively. The wavelength resonator devices have many applications in optical communications including wavelength filtering, routing, switching, modulating, multiplexing, optic buffer, and demultiplexing. We use the free carrier plasma dispersion effect to design the switch of SOI buffer and Photonic crystal Bandgap (PBG) waveguide buffer devices are simulated by Finite Difference Time Domain (FDTD) methods. The technology have made it possible to create micrometer-size photonics devices based on reasonably low-loss semiconductor waveguides. To characterize SOI buffer waveguides delays, the analysis of wavelength response, the number of propagation modes and the waveguide loss are investigated at wavelength 1.55μm.