Geometric control over surface plasmon polariton out-coupling pathways in metal-insulator-metal tunnel junctions

• Published in: Optics express Vol. 29; no. 8; pp. 11987 - 12000
• Main Authors: Radulescu, Andreea, Makarenko, Ksenia S, Hoang, Thanh Xuan, Kalathingal, Vijith, Duffin, Thorin J, Chu, Hong-Son, Nijhuis, Christian A
• Format: Journal Article
• Language: English
• Published: United States 12.04.2021
• ISSN: 1094-4087; 1094-4087
• 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.