A theory of multimode traveling-wave modulators for RF photonics

This paper presents a rigorous and general approach to the analysis of multimode traveling-wave electrooptical modulators. Starting from the linear model derived by Di Donato et al. in 2004, where we demonstrated the accuracy of this approach for single mode electrooptic modulators and for quasi-degenerate modes, we now provide a compact, analytical solution to the system of coupled transmission-line equations describing multimode and multipolarization interaction. In addition, the analysis will consider the joint effect of a continuous and a time-space varying voltage. Small dielectric perturbations induced by the microwave fields (Δε≪ε) and large difference between the optical and modulating signal frequencies are the only hypotheses used in deriving the linear model by Di Donato et al. Some examples are discussed in order to demonstrate the main characteristics of the electrooptic modulators and some suggestions on the electrooptic modulator design are provided in order to realize polarization-independent devices.