Guided-wave intensity modulators using amplitude-and-phase perturbations

A theoretical analysis of intensity modulation in coupled waveguides and Mach-Zehnder interferometers is reported. Simultaneous phase and amplitude perturbations Delta n+ iota Delta k are considered. Predictions are made about the performance of electrooptic GaAs and InP modulators controlled by the free-carrier effect ( Delta N) or by the Franz-Keldysh effect ( Delta E). The phase-dominant condition Delta n>5 Delta k is optimal. The predicted depth of modulation is greater than that of conventional loss-modulators over a range of Delta N or Delta E.>