Directional launching of surface plasmon polaritons by electrically driven aperiodic groove array reflectors

Abstract

Access to surface plasmon polaritons (SPPs) with directional control excited by electrical means is important for applications in (on-chip) nano-optoelectronic devices and to circumvent limitations inherent to approaches where SPPs are excited by optical means (e.g., diffraction limit). This paper describes directional excitation of surface plasmon polaritons propagating along a plasmonic strip waveguide integrated with an aperiodic groove array electrically driven by an Al–Al2O3–Au tunnel junction. The aperiodic groove array consists of six grooves and is optimized to specifically reflect the SPPs by 180° in the desired direction (+x or −x) along the plasmonic strip waveguide. We used constrained nonlinear optimization of the groove array based on the sequential quadratic programming algorithms coupled with finite-difference time-domain (FDTD) simulations to achieve the optimal structures. Leakage radiation microscopy (Fourier and real plane imaging) shows that the propagation direction of selectively only one SPP mode (propagating along the metal–substrate interface) is controlled. In our experiments, we achieved a directionality (i.e., +x/−x ratio) of close to 8, and all of our experimental findings are supported by detailed theoretical simulations.

CMOS‐Compatible Electronic–Plasmonic Transducers Based on Plasmonic Tunnel Junctions and Schottky Diodes

“…The right outermost arc in Figure 2 is due to both the scattering and leakage radiation of the right-propagating Cu-glass SPPs. [23] The third feature appearing along the inner circle (k/k 0 ≈ 1) represents the Cu-air SPP that approaches the Cu waveguide end. This waveguide end scatters the Cu-air SPPs to photons.…”

“…[3][4][5] Most plasmonic components, however, are optically driven by off-chip light sources [6,7] and limited to to control the direction of SPP excitation and propagation from tunnel junctions by integration of edge-to-edge nanorods, [20] Yagi-Uda antennas, [21,22] or aperiodic gratings. [23] Furthermore, tunneling junctions are arguably the smallest possible plasmon sources that can be scaled down to the nanometer scale. For instance, plasmonic tunnel junctions are routinely made with tips of scanning tunneling microscopes.…”

“…[46] Although impressive progress has been made toward improving the properties of plasmonic components, integration of different plasmonic components in electronic-plasmonic transducers is rare. For example, ultrafast temporal modulation (>1 GHz) of light emission, [15] directional plasmon excitation, [23,47] or highly efficient plasmon excitation [48] has been demonstrated for tunnel junctions equipped resonant structures. To utilize SPPs as information carriers, it is desirable to write and read out plasmonic signals via electrical means.…”

Spatial Control over Stable Light‐Emission from AC‐Driven CMOS‐Compatible Quantum Mechanical Tunnel Junctions

“…[4,[10][11][12] Inelastic tunneling can also be utilized to excite SPP modes propagating along plasmonic waveguides. [13][14][15] Directional control over SPPs and light emission has also been demonstrated via the integration of optical elements, such as gratings, [16] nanoantennas, [17] nanoparticles, [18] Yagi-Uda antennas, [19] and tilted self-assembled monolayers. [20] This paper describes a new method to manipulate the location of SPP/photon excitation within large-area junctions by tuning the tunneling current density via engineering of the tunnel oxide thickness.…”

Geometric Control Over the Edge Diffraction of Electrically Excited Surface Plasmon Polaritons by Tunnel Junctions

“…Compared to optical excitation schemes, where the position of the plasmonic waveguide within the laser waist beam has to be precisely controlled in order to excite SPPs close to the edges of the waveguide, 30,35,42−44 in MIM-TJs connected to plasmonic waveguides, SPPs can easily be excited across the entire width of the waveguides and the edge diffraction can easily be obtained as previously observed. 38,39,41,45 Additionally, the edge diffraction clearly separates the metal−air leaky SPP contributions from those of the metal−glass SPPs, which can only be detected via scattering at the end of the waveguide due to the bound nature of the modes. 38,46 Hence, an integrated structure where the MIM-TJ is in-plane with a plasmonic stripe waveguide offers an efficient platform for investigating the SPP edge diffraction.…”