The optical waveguide design of quantum well EA traveling-wave modulator is investigated by the evaluation criteria, which contain material parameters, couple loss, microwave properties. The result shows that the material design is very important for good performance, and the thickness of core layer is larger than absorption layer is better and the thickness of active layer should be optimized.
For high-speed traveling-wave modulator, impedance match, velocity match and low microwave attenuation are important. But they have different effects on bandwidth for different structure and scheme for quantum well electroabsorption modulator and bulk Mach-Zehnder electrooptic modulator. For bulk Mach-Zehnder electrooptic modulator, the longer active waveguide is needed, and at such situation, according to the normalized gain (or modulation reduction factor) the velocity match and impedance match and low microwave attenuation should be well satisfied to achieve good performance. While for the quantum well electroabsorption modulator, limited by the optical loss, short active waveguide must be used. When the device length is largely reduced match requirement is not so strict and it is also difficult to achieve good match. Low terminator electroabsorption modulator is reported recently. Its concept could be inferred from the normalized gain formula. And some technology tendency in traveling-wave electroabsorption and Mach-Zehnder modulator could be also obtained and could explain series of experiment. From calculation and experiment the low impedance and low terminator could expand the bandwidth by slight mismatch. The relation of modulator characteristic impedance, microwave phase velocity and microwave attenuation is not much considered for simplification. The results are useful to design and optimize modulator.
A novel structure ofGaAs/GaAIAs multi-quantum well (MQW) traveling wave (TW) Mach-Zehnder modulator (MZM) with coplanar strips is proposed. This device uses n+ heavy doped layer to obtain velocity match. Then the Method of Lines is applied to characterize the influence ofmetallization thickness and conductivity loss on the velocity match and impedance match. With optimum parameters ofthe structure, the bandwidth over 80GHz is obtained.
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