Borghi M, Mancinelli M, Merget F, Witzens J, Bernard M, Ghulinyan M, Pucker G, Pavesi L
Opt Lett. 2015 Nov 15;40(22):5287-90. doi: 10.1364/OL.40.005287.
The observation of the electro-optic effect in strained silicon waveguides has been considered a direct manifestation of an induced χ(2) nonlinearity in the material. In this work, we perform high-frequency measurements on strained silicon racetrack resonators. Strain is controlled by a mechanical deformation of the waveguide. It is shown that any optical modulation vanishes, independent of the applied strain, when the applied voltage varies much faster than the carrier effective lifetime and that the DC modulation is also largely independent of the applied strain. This demonstrates that plasma carrier dispersion is responsible for the observed electro-optic effect. After normalizing out free-carrier effects, our results set an upper limit of (8±3) pm/V to the induced high-speed effective χeff,zzz(2) tensor element at an applied stress of -0.5 GPa. This upper limit is about 1 order of magnitude lower than previously reported values for static electro-optic measurements.
在应变硅波导中观察到的电光效应被认为是材料中诱导χ(2)非线性的直接表现。在这项工作中，我们对应变硅环形谐振器进行了高频测量。应变通过波导的机械变形来控制。结果表明，当施加电压的变化速度比载流子有效寿命快得多时，任何光调制都会消失，且与施加的应变无关，同时直流调制在很大程度上也与施加的应变无关。这表明等离子体载流子色散是观察到的电光效应的原因。在消除自由载流子效应后，我们的结果给出了在-0.5 GPa的外加应力下，诱导的高速有效χeff,zzz(2)张量元素的上限为(8±3) pm/V。这个上限比之前报道的静态电光测量值低约1个数量级。
