Parasitic phase modulation in single drive Mach-Zehnder optical modulator

The single drive Mach-Zehnder interferometer modulator is used basically for optical intensity modulation. It is well known that its modulation characteristic exhibits a significant nonlinearity at increased drive level. However, we draw the attention to the problem that the intensity modulation is associated with a parasitic phase modulation. In this paper we investigate the source of parasitic phase modulation and its effect on the resultant modulation characteristic.