Effect of device length and background doping on the relative magnitudes of phase and amplitude modulation in GaAs/AlGaAs PIN multiple quantum well waveguide optical modulators

In this paper we present a model for the behavior of a PIN waveguide optical modulator utilizing the quantum confined Stark effect. The model uses experimental data to determine the electric field dependence of absorption coefficient and refractive index changes in 100-A GaAs/100-A Al(0.3)Ga(0.7)As quantum wells, and then uses these data to model a symmetric waveguide structure with a core full of quantum wells. We have determined general design rules for the background doping and length of low chirp amplitude modulators and phase modulators with low amplitude modulation. The chief results are that the doping should be high for an amplitude modulator and low for a phase modulator, and in both cases the device should be kept short.