The development of external modulators is fundamental since the presence of chirping deteriotates the direct modulation of laseres ati high frequencies. In this work a project of an amplitude modulator for high bit-rate telecommunication systems using the Stark effect in semiconductors was undertaken. In the proposed semiconductor structure the electro-absorption in InGaAs/AnAlAs multiple quantum wells was used. Different figures of merit of the passive and active device were analysed. In the simulation of the device performance as a waveguide the following methods were applied: effective Index Method and Beam Propagation Method. The applicability of these methods were tested on a GaAs/AlGaAs rib structure and the results were compared with measurements done in the laboratory. The experimental results were in completed accord with the simulation. Therefore, the same methods were used to evaluate the proposed amplitude modulator structure. The resulting performance of the waveguide corresponds to the desired characteristics.