We introduce a nanoplasmonic isolator consisting of a cavity coupled to a metal-dielectric-metal (MDM) waveguide. The waveguide and cavity are filled with a magneto-optical (MO) material, and the structure is under a static magnetic field. We show that, when MO activity is present, the cavity becomes a traveling wave resonator with unequal decay rates into the forward and backward directions. As a result, the structure operates as an isolator. We also introduce non-Hermitian plasmonic waveguide-cavity systems with topological edge states (TESs) at singular points. The structure unit cells consist of an MDM waveguide side-coupled to MDM stub resonators with modulated distances between adjacent stubs. In such structures the modulated distances introduce an effective gauge magnetic field. We show that such structures achieve extremely high sensitivity of the reflected light intensity. TESs at singular points could lead to singularity-based plasmonic devices with enhanced performance.
The magneto-optical effect has been used to control the propagation of surface plasmon polaritons in plasmonic waveguides. Here we investigate single-interface metal-dielectric and metal-dielectric-metal plasmonic waveguides in which either the dielectric or the metal is a magneto-optical material. We derive the dispersion relation of these waveguides, and investigate the effect of an externally applied static magnetic field. We find that in metal-dielectric-metal waveguide structures in which the dielectric is a magneto-optical material, the symmetry of the structure prohibits any non-reciprocal propagation in the system. Moreover, the induced change in the propagation constant of the supported modes in the presence of an externally applied static magnetic field is relatively small. In addition, we find that using a magneto-optical metal in a single-interface metal-dielectric plasmonic waveguide results in non-reciprocal propagation of the plasmonic modes along the interface. We also find that in metal-dielectric-metal plasmonic waveguides in which the metal is a magneto-optical material, the propagation constant of the supported modes is dependent on the relative direction of the applied magnetic fields to the upper and lower metal regions. If the applied magnetic fields to the two metal regions are equal and in the same direction, the induced changes in the propagation constants of the modes propagating in the positive and negative directions are the same. On the other hand, if the directions of the applied external magnetic fields are opposite, the propagation constants of the modes propagating in the positive and negative directions are different. We finally investigate Fabry-Perot cavity magneto-optical switches.
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