An investigation of all-optical wavelength conversion based on semiconductor optical amplifier (SOA) and delay interferometer (DI) scheme is presented. The working principle of SOA-DI configuration is explained and the functions of DI parameters are analyzed. Experiments of wavelength conversion at 10 Gb/s and 40 Gb/s for return-to-zero format are demonstrated. The experimental results show that wavelength conversion exploiting cross-gain modulation leads to reversed polarity and degradation of extinction ratio (ER) for the converted signal, and the performance of the wavelength conversion at a high bit rate is degraded. In addition, the results show that the wavelength conversion based on SOA-DI scheme can preserve the data polarity and improve the ER of the converted signal so that the performance of wavelength conversion using one single SOA is improved and the system can operate at a high bit rate. The SOA-DI scheme has advantages of compactness and photonic integration potential.