Third order optical nonlinearities in graphene have been demonstrated to be large and have been predicted to be highly dependent on the Fermi energy of the graphene. This prediction suggests that graphene can be used to make systems with large and electrically tunable optical nonlinearities. In this work, we present what is to our knowledge the first experimental observation of this Fermi energy dependence of the optical nonlinearity. We have performed a degenerate four-wave mixing experiment on a silicon nitride (SiN) waveguide covered with graphene which was gated using a polymer electrolyte. We observe strong dependencies of the four-wave mixing conversion efficiency on the signal-pump detuning and Fermi energy, that is, the optical nonlinearity is indeed demonstrated to be electrically tunable. In the vicinity of the interband absorption edge (2|E_F| ≈ ℏω), a peak value of the waveguide nonlinear parameter of ≈6400 m^–1W⁻¹, corresponding to a graphene nonlinear sheet conductivity |σ_s⁽³⁾| ≈ 4.3 × 10^–19 A m²V^–3, is measured. These results were qualitatively linked with theoretical calculations. Apart from providing a better understanding of the nonlinear optical response of graphene, these observations could pave the way toward the use of graphene for tunable nonlinear optics.

中文翻译：

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以四波混频为特征的石墨烯覆盖的SiN波导中的电可调光非线性

已经证明石墨烯中的三阶光学非线性很大，并且已经预测其高度依赖于石墨烯的费米能。该预测表明，石墨烯可用于制造具有大的和电可调的光学非线性的系统。在这项工作中，我们将介绍我们对光学非线性的费米能量依赖性的第一个实验观察结果。我们已经对覆盖有石墨烯的氮化硅（SiN）波导进行了简并的四波混合实验，该波导是使用聚合物电解质进行选通的。我们观察到四波混频转换效率对信号泵失谐和费米能量的强烈依赖性，也就是说，光学非线性确实被证明是电可调的。E _F | ≈ℏω）≈6400米的波导非线性参数的峰值^-1 w ^ ^-1，对应于石墨烯片非线性电导率|σ_小号^（3） | 测量≈4.3×10 ^–19 A m ² V ^–3。这些结果在质量上与理论计算联系在一起。除了更好地了解石墨烯的非线性光学响应外，这些发现还可以为将石墨烯用于可调非线性光学技术铺平道路。