A new calibration method of optoelectronic frequency response for optical-to-electrical (O/E) conversion devices is proposed. The method is based on a conventional heterodyne measurement principle, but utilizes a Mach-Zehnder modulator for generating two-tone lightwaves as standard stimulus signals. Four requirements needed for such signals are given and the techniques to satisfy them are discussed. Trial calibration results are also demonstrated. The proposed method is simpler and easier than the conventional method utilizing a complex two-laser system phase-locked with each other.