School of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
Institute for Research in Electronics and Applied Physics, University of Maryland , College Park, Maryland 20742, United States.
Nano Lett. 2018 Feb 14;18(2):740-746. doi: 10.1021/acs.nanolett.7b03919. Epub 2018 Jan 23.
Fabry-Pérot metal-insulator-metal (MIM) nanocavities are widely used in nanophotonic applications due to their extraordinary electromagnetic properties and deeply subwavelength dimensions. However, the spectral response of nanocavities is usually controlled by the spatial separation between the two reflecting mirrors and the spacer's refractive index. Here, we demonstrate static and dynamic control of Fabry-Pérot nanocavities by inserting a plasmonic metasurface, as a passive element, and a gallium doped-zinc oxide (Ga:ZnO) layer as a dynamically tunable component within the nanocavities' spacer. Specifically, by changing the design of the silver (Ag) metasurface one can "statically" tailor the nanocavity response, tuning the resonance up to 200 nm. To achieve the dynamic tuning, we utilize the large nonlinear response of the Ga:ZnO layer near the epsilon near zero wavelength to enable effective subpicosecond (<400 fs) optical modulation (80%) at reasonably low pump fluence levels (9 mJ/cm). We demonstrate a 15 nm red shift of a near-infrared Fabry-Pérot resonance (λ ≅ 1.16 μm) by using a degenerate pump probe technique. We also study the carrier dynamics of Ga:ZnO under intraband photoexcitation via the electronic band structure calculated from first-principles density functional method. This work provides a versatile approach to design metal nanocavities by utilizing both the phase variation with plasmonic metasurfaces and the strong nonlinear response of metal oxides. Tailorable and dynamically controlled nanocavities could pave the way to the development of the next generation of ultrafast nanophotonic devices.
法布里-珀罗金属-绝缘体-金属（MIM）纳米腔由于其非凡的电磁特性和深亚波长尺寸，在纳米光子学应用中得到了广泛的应用。然而，纳米腔的光谱响应通常由两个反射镜之间的空间分离和间隔层的折射率来控制。在这里，我们通过在纳米腔的间隔层中插入一个等离子体超表面作为无源元件和一个掺镓氧化锌（Ga:ZnO）层作为动态可调谐元件，演示了法布里-珀罗纳米腔的静态和动态控制。具体来说，通过改变银（Ag）超表面的设计，可以“静态”地调整纳米腔的响应，将共振调谐高达 200nm。为了实现动态调谐，我们利用 Ga:ZnO 层在近零折射率波长附近的大非线性响应，在合理低的泵浦强度水平（9mJ/cm）下实现有效的亚皮秒（<400fs）光学调制（80%）。我们利用简并泵浦探测技术，演示了近红外法布里-珀罗共振（λ≈1.16μm）的 15nm 红移。我们还通过第一性原理密度泛函方法计算的电子能带结构研究了 Ga:ZnO 在带内光激发下的载流子动力学。这项工作提供了一种通过利用等离子体超表面的相位变化和金属氧化物的强非线性响应来设计金属纳米腔的通用方法。可调谐和动态控制的纳米腔可能为开发下一代超快纳米光子器件铺平道路。
