Different effects on bandwidth for traveling-wave quantum well electro-absorption modulator and bulk Mach-Zehnder electric-opto modulator

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.