Phase matched transmission line design for high-speed optical modulators

In this paper we present a transmission line design to achieve phase matched lines for high-speed optical modulators. The layout presented is for transmission lines that start off equally spaced. The mathematical relation to achieve phase matching between the lines is derived by making the path length difference zero. Example transmission line layouts using co-planar waveguide are generated based upon the specifications of some Mach-Zehnder Modulators (MZM) and in-phase/quadrature (IQ) MZMs that have been designed. The design method is then verified by comparing the phase of the transmission lines in a commercial full-wave electromagnetic program.