硅光波导和光子器件具有大折射率差和紧凑尺寸，硅光子被认为是新一代大规模光电集成技术。基于自由载流子等离子体色散效应，采用MOS电容电极结构的马赫曾德尔调制器(MZM)，可实现10 GHz以上的高速调制。采用有限元方法，通过构建光和电结合模拟方法，对一种双硅层的MOS电容电极MZM的静态和动态性能进行了理论研究。研究结果表明，在-2 V驱动电压作用下，当掺杂粒子浓度为1×1015 cm-3时，有效折射率变化值为1.05×10-5左右，实现Vπ所需的单臂调制臂长为3.68 cm，损耗小于0.84 dB/cm，其上升时间和下降时间在40 ps左右；当掺杂粒子浓度为5×1015 cm-3时，其有效折射率变化只有0.86×10-5左右，实现Vπ所需的单臂调制臂长需4.51 cm，损耗约为1.36 dB/cm。当改变该调制器结构参数后，其上升时间和下降时间会产生明显变化。

Silicon photonics is a novel technique for large-scale optic-electronic integration, with which most kinds of optical devices can be designed. Based on free-carrier plasma dispersion, silicon Mach-Zehnder electro-optic modulator (MZM) can achieve high modulation speed over 10 GHz. Considering the need for modulation speed and power consumption, a kind of silicon MZM based on MOS capacitor electrodes is studied by a simulation method combining electric and optic analytic model. The results show that under the driving voltage of -2 V, when the doping concentration is 1×1015 cm-3, the effective refractive index change of the optical waveguide in silicon MZM is about 1.05×10-5, which results in single modulation arm length of 3.68 cm to realize Vπ and the loss of less than 0.84 dB/cm. When doping concentration is 5×1015 cm-3, the effective refractive index change is only 0.86×10-5, which results in the Vπ length of 4.51 cm and the loss of about 1.36 dB/cm. And varied capacitor electrode structures of silicon MZM may make the visible difference of the modulation performance, including the rise and fall time.