We have proposed, simulated, and experimentally verified the novel automatic control method and apparatus to automatically adjust and constantly maintain the optimum optical gain and phase differences in order to achieve the automatically optimized semiconductor optical amplifier (SOA)–Mach-Zehnder interferometer (MZI) wavelength converter (WC) with wide input power dynamic range (IPDR) and maximum extinction ratio (ER). Our automatic control algorithm is proposed through the results of simulation and its validity is confirmed through the experiment.