In this paper, by employing two practical methods of multi-electrode design and tapered waveguide structure, compensation techniques to restore declining carrier density along the quantum dot semiconductor optical amplifier's waveguide are investigated. In the multi-electrode method, the effects of distributing current via electrodes on the gain and the cross-gain modulation for two, three and four-electrode structures are studied. These characteristics are also investigated for the quantum dot semiconductor optical amplifiers with a tapered waveguide structure for the first time, including waveguides with different profiles and width ratios. After due comparison between these two methods, optimum parameters of the two techniques will be used simultaneously along each other to form a combined method. Through these design developments, gain as the main feature of the quantum dot semiconductor optical amplifiers continuously increases, though cross-gain modulator results show that there is a trade-off between the modulation efficiency and improving structure capability of restoring carrier density.
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