A wavelength channel data rewriter (WCDR) is a device that erases the data on an incoming signal by utilizing the saturation characteristic of a semiconductor optical amplifier (SOA) and then modulates it with new data to generate an upstream signal. This paper describes a theoretical and experimental investigation designed to improve the performance of the WCDR. Through numerical calculations, this paper shows that an SOA with a long waveguide with a large small-signal gain better suppresses optical bit patterns. This paper also uses calculated and experimental results to show that the amplified-spontaneous-emission noise in the SOA input signal degrades the bit-pattern suppression. This paper then describes the semiconductor optical saturator/modulator (SOSM), which this paper has developed for use in the WCDR based on the results of the author's theoretical investigations. This paper outlines the SOSM specifications and provides experimental results that confirm the improved WCDR performance obtained using the SOSM.