What are plasmonic disks

Concepts for new switchable plasmonic nano components

Plasmonic waveguides open up the possibility of developing dramatically reduced optical components and provide a promising route to future technologies for integrated circuits for information processing, optical computing, and others. The main elements of nanophotonic circuits are controllable routers and plasmonic modulators. Recently, Dr. Joachim Herrmann from MBI in cooperation with external partners new concepts for the realization of such nanocomponents. They studied the propagation of surface plasmon polaritons (SPPs) in magneto-plasmonic waveguides. Based on the results of this study, they proposed new variants of controllable magneto-plasmonic routers and magneto-plasmonic disc modulators for different functionalities.

In a waveguide made of a metallic film with a thickness exceeding the skin depth and surrounded by a ferromagnetic dielectric material, an external magnetic field causes a spatial asymmetry of the mode distribution of surface plasmon polaritons (SPP). The superposition of the even and the odd modes leads, after a certain propagation length, to a concentration of the SPP energy on one surface of the metallic layer, which can be switched to the opposite surface by changing the direction of the magnetic field. Based on this phenomenon, the group proposes a new type of waveguide-integrated magnetically controlled switchable router. A diagram of such a nanocomponent is shown in Fig. 1, which consists of a T-shaped metallic waveguide which is surrounded by a ferromagnetic dielectric material and is under the action of an external magnetic field leading to a magnetization M. Fig. 2 shows the results of a numerical solution of the Maxwell equations for the SPP propagation in this structure. As can be seen, a change in direction of the magnetic field causes a channel switch with 99% contrast within an optical bandwidth of 10 THz. Here g is the gyration g = χ M, χ is the magneto-optical susceptibility and g0 is a characteristic gyration, which is necessary for a significant mode asymmetry. A change in direction of the magnetic field can be generated by integrated electrical circuits with a repetition rate in the GHz range. So far, only a few articles have reported on the realization of switchable plasmonic routers that are based on branched silver wires and are controlled by the polarization of the incident light.

In a second publication, the group proposed a new variant of a nanometer plasmonic modulator, which is based on a metal-insulator-metal waveguide and a laterally coupled magneto-optical disk resonator and is controlled by an external magnetic field (see Fig. 3). A change in the wave number and the transmission of SPP modes can be caused by a change in the magnetic field. On / off switching of running SPP modes through this component as a result of a reversal of the direction of the magnetic field is demonstrated by the numerical solution of the Maxwell equations.An increase in resonance of the magneto-optical modulation by more than a factor of 200 leads to a contrast rate of more than 90% moderate transmission loss within a bandwidth of more than 100 GHz. Figure 4 shows the distribution of the magnetic field component of the SPP modes at a gyration of g = 0.03 and g = -0.03. As can be seen, a change in the direction of the external magnetic field due to the change in the interference pattern from an "off" to an "on" state of the magneto-plasmonic modulator.