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We study the influence of ion implantation conditions on the performance of depletion-type silicon optical modulators by a combined simulation of the process flow, the electrical characteristic, and the beam propagation. Through calculations using different implantation positions, energies, and tilt angles, this paper reveals that a gap between specific implantation windows is able to alleviate the modulation efficiency degradation due to the lateral straggling of implanted ions, while a tilt angle reduces the optical loss without harming the modulation efficiency. After an optimization of the implantation condition, the extinction ratio of the Mach-Zehnder modulator can be improved by 4.6 dB, while its optical loss falls from 3 to 2.47 dB. Finally, a simplified doping pattern that eliminates two implantation steps is discussed.