Abstract
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.
Highlights
Surface plasmon polaritons (SPPs) confine electromagnetic fields at dielectric–metal interfaces [1] and are promising candidates for applications in subwavelength imaging [2], sensing [3], and other areas in nanotechnology [4,5,6], because of strong field enhancement and their capability to overcome the diffraction limit [7]
Access to surface plasmon polaritons (SPPs) with directional control excited by electrical means is important for applications in nano-optoelectronic devices and to circumvent limitations inherent to approaches where SPPs are excited by optical means
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
Summary
Surface plasmon polaritons (SPPs) confine electromagnetic fields at dielectric–metal interfaces [1] and are promising candidates for applications in subwavelength imaging [2], sensing [3], and other areas in nanotechnology [4,5,6], because of strong field enhancement and their capability to overcome the diffraction limit [7]. For the first time, unidirectional SPP excitation along a plasmonic waveguide from an aperiodic groove array (designed to reflect propagating SPPs by 180°) electrically driven by a quantum mechanical tunnel junction. Metallic groove array with the same depth but with different widths of, and distances between, the grooves was designed by gradient descent algorithm for the excitation of unidirectional SPPs with a directionality up to 55 [11] Such aperiodic structures have not been used as reflectors to alter the propagation directional of the SPPs, as we show here, by 180°-driven tunnel junctions.
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