Study Of 40GHz GaAs Traveling Wave Multiple Quantum Well Electro-optic Modulators

The upgrade of the backbone network from the 10Gb to 40Gb has been a worldwide tide. Many laboratories and companies all over the world are focusing on the research and fabrication of devices with 40GHz bandwidth. In China,with the dramatically increasing demand of the communication capacity,the future backbone network will no doubt rely on lOGb/b or faster devices. This trend makes it a pressing need to develop more promising modulators,one of the key components in optical communications. In this dissertation,a novel M-Z high speed modulator is proposed,analyzed,fabricated and measured,employing multiple quantum well (MQW) structures and traveling wave (TW) electrodes to meet the demand of low voltage and wide bandwidth.The performance of modulators employing MQW is governed by the quantum confined Stark Effect. In order to simplify the analysis of MQW,we obtain an explicit formula concerning the correlations between the GaAs/GaAlAs quantum well widths of finite potential barrier structure and those of infinite potential barrier structure under the condition that the ground state energies are equal at zero bias states. Then the transfer matrix method is used to investigate the optical field distribution in the MQW waveguide based on five-step asymmetric coupled quantum well structure that is really used in the modulator. It demonstrates that this structure shows large birefringence that needs more consideration. The absorption characteristics are also been discussed.In this modulator,coplanar strips (CPS) are used as electrodes for they support balance mode propagation of microwave,and this is a desired merit for common optical modulator. Due to the miniaturized dimensions,the metallization thickness is in the order of skin depth and the conductor losses are not negligible. Therefore,the Method of Lines is applied to characterize the influence of metallization thickness and conductivity loss on the velocity match and impedance match.Meanwhile,we discuss the static electric field distribution in anisotropic materials caused by the applied voltage on the electrodes,which will help to decrease the driving voltage.Finally,the device was fabricated during the course of this research. And measured data,including the static response and spectrum,are obtained.