Radulescu Andreea, Makarenko Ksenia S, Hoang Thanh Xuan, Kalathingal Vijith, Duffin Thorin J, Chu Hong-Son, Nijhuis Christian A
Opt Express. 2021 Apr 12;29(8):11987-12000. doi: 10.1364/OE.413698.
Metal-insulator-metal tunnel junctions (MIM-TJs) can electrically excite surface plasmon polaritons (SPPs) well below the diffraction limit. When inelastically tunneling electrons traverse the tunnel barrier under applied external voltage, a highly confined cavity mode (MIM-SPP) is excited, which further out-couples from the MIM-TJ to photons and single-interface SPPs via multiple pathways. In this work we control the out-coupling pathways of the MIM-SPP mode by engineering the geometry of the MIM-TJ. We fabricated MIM-TJs with tunneling directions oriented vertical or lateral with respect to the directly integrated plasmonic strip waveguides. With control over the tunneling direction, preferential out-coupling of the MIM-SPP mode to SPPs or photons is achieved. Based on the wavevector distribution of the single-interface SPPs or photons in the far-field emission intensity obtained from back focal plane (BFP) imaging, we estimate the out-coupling efficiency of the MIM-SPP mode to multiple out-coupling pathways. We show that in the vertical-MIM-TJs the MIM-SPP mode preferentially out-couples to single-interface SPPs along the strip waveguides while in the lateral-MIM-TJs photon out-coupling to the far-field is more efficient.
金属-绝缘体-金属隧道结（MIM-TJs）能够在远低于衍射极限的情况下电激发表面等离激元极化激元（SPPs）。当非弹性隧穿电子在外部施加电压下穿过隧道势垒时，会激发一种高度受限的腔模（MIM-SPP），该腔模会通过多种途径进一步从MIM-TJ向外耦合为光子和单界面SPP。在这项工作中，我们通过设计MIM-TJ的几何结构来控制MIM-SPP模式的外耦合途径。我们制造了隧穿方向相对于直接集成的等离激元条形波导垂直或横向的MIM-TJs。通过控制隧穿方向，实现了MIM-SPP模式优先向外耦合为SPP或光子。基于从后焦平面（BFP）成像获得的远场发射强度中单个界面SPP或光子的波矢分布，我们估计了MIM-SPP模式向多种外耦合途径的外耦合效率。我们表明，在垂直MIM-TJs中，MIM-SPP模式优先沿着条形波导向外耦合为单个界面SPP，而在横向MIM-TJs中，光子向外耦合到远场的效率更高。
