Mach-Zehnder Modulator Performance Tradeoffs in Modern Microwave Photonic Systems: Z & X-Cut

Lithium Niobate based Mach-Zehnder modulators are widely used in broadband, microwave photonic transmission systems due to their excellent optical characteristics and their high frequency modulation bandwidths. State of the art modulators can support instantaneous RF bandwidths from DC to greater than 60 GHz, which is enabling industry leaders to deliver high performance fiber optic transmission of RF signals over distances exceeding 200 kms.Mach-Zehnder based transmitters are employed in a wide range of applications.Lithium Niobate Mach-Zehnder modulators are available in two basic configurations that refer to the orientation of the LiNbO3 crystal. These are typically designated as Z-cut and X-cut modulators.

While the basic operation of these two types of modulators are similar, there are some significant differences that a system designer should be cognizant of when employing a photonic transmitter that contains either type of modulator.This paper will briefly describe the differences between these modulator technologies and highlight associated system level impacts.