Analysis of depletion edge translation lightwave modulators

Presents a complete analysis of waveguide phase modulators based on the depletion-edge-translation concept. The phenomena taking place inside the depletion region which contribute to changing the refractive index there are studied. It is shown that the behavior of these modulators can be understood in terms of two electric field-related and two carrier-related effects: linear electrooptic, electrorefractive, plasma, and band filling. The sum of the refractive index variations produced by each one of these effects, taking into account the waveguide geometry, accounts quantitatively for the experimental phase shifts measured in the devices. No fitting parameters are used and a very good agreement between theory and experiment is obtained. Based on this theory, an analysis of the device is made in terms of the optimum values for the doping in the waveguide, and also in terms of the wavelength dependence of the device phase modulation properties