近年来，硅光子学由于其在集成光子元件（1，2）以及全介电元光学元件中的潜力而引起了极大的兴趣。(3)强的光子-光子相互作用，又称光学非线性，实现了对上述光子器件的主动控制。（4，5）然而，Si的固有非线性太弱，无法设想实际应用。为了提高非线性响应，已经采用了长的相互作用长度结构，例如波导，或者谐振结构，例如微谐振器或光子晶体。（6，7）然而，它们的特征尺寸通常大于10 $μ$ m，比它们的电子对应物大得多。在这里，我们发现，当减少硅谐振腔的尺寸下降到~100 nm，一个巨大的光热非线性，产生400%的可逆和可重复的偏离线性散射响应在低激发强度（mW/ $μ$ m $^2$）。纳米尺度下的等效非线性折射率n $_2$比体相的大五个数量级，这是由于热隔离纳米结构中的Mie共振增强吸收和高效加热。此外，纳米尺度的热弛豫时间达到纳秒，意味着GHz的调制速度。这种大而快的非线性使其应用于纳米级的全光控制以及硅的超分辨率成像。
英文摘要：
Silicon photonics has attracted significant interest in recent years due to its potential in integrated photonics components (1,2) as well as all-dielectric meta-optics elements.(3) Strong photon-photon interactions, aka optical nonlinearity, realizes active control of aforementioned photonic devices.(4,5) However, intrinsic nonlinearity of Si is too weak to envision practical applications. To boost the nonlinear response, long interaction-length structures such as waveguides, or resonant structures such as microring resonators or photonic crystals have been adopted.(6,7) Nevertheless, their feature sizes are typically larger than 10 $μ$m, much larger than their electronic counterparts. Here we discover, when reducing the size of Si resonator down to ~100 nm, a giant photothermal nonlinearity that yields 400% reversible and repeatable deviation from linear scattering response at low excitation intensity (mW/$μ$m$^2$). The equivalent nonlinear index n$_2$ at nanoscale is five-order larger than that of bulk, due to Mie resonance enhanced absorption and high-efficiency heating in the thermally isolated nanostructure. In addition, the nanoscale thermal relaxation time reaches nanosecond, implying GHz modulation speed. This large and fast nonlinearity enables applications toward all-optical control in nanoscale, as well as super-resolution imaging of silicon.
