New Switchable Plasmonic Nanodevices

Magnetic field distribution of the surface-plasmon-polaritons in a metal waveguide side-coupled to a disk resonator at the wavelength of 748 nm. The metal waveguide is made from silver and the ferromagnetic dielectric from Bi-substituted iron garnet. (Source: MBI)

Plasmonic wave­guides open the possi­bility to develop drama­tically minia­turized optical devices and provide a promising route towards the next-generation of inte­grated nano­photonic circuits for infor­mation processing, optical computing and others. Key elements of nano­photonic circuits are switchable plasmonic routers and plasmonic modulators. Recently, Joachim Herrmann at Max-Born-Institute in Berlin MBI and his external colla­borators developed new concepts for the reali­zation of such nanodevices. They inves­tigated the propa­gation of surface-plasmon-polari­tons (SPP) in magneto-plasmonic waveguides. Based on the results they proposed new variants of switchable magneto-plasmonic routers and magneto-plasmonic disk modulators for various nano­photonic func­tionalities.

In a waveguide based on a metal film with a thickness exceeding the Skin depth and surrounded by a ferro­magnetic dielectric an external magnetic field in the transverse direction can induce a signi­ficant spatial asymmetry of mode distri­bution of surface-plasmon-polaritons (SPP). Super­position of the odd and the even asymmetric modes over a certain distance leads to a concen­tration of the energy on one interface which is switched to the other interface by magnetic field reversal. The requested magni­tude of magnetization is exponen­tially reduced with the increase of the metal film thickness. Based on this pheno­menon, the group proposed a new type of waveguide-inte­grated magne­tically controlled switchable plasmonic routers.

The nano­device consists of a T-shaped metallic waveguide surrounded by a ferro­magnetic dielectric under an external magnetic field inducing a magne­tization. Numerical results for the plasmon propa­gation by solving the Maxwell equation show channel switching by the magnetic field reversal with a 99%-high contrast within the optical bandwidth of tens of THz. Magnetic field reversal by inte­grated electronic circuits can be realized with a repe­tition rate in the GHz region. Note that up to now there exist only few results reporting the reali­zation of switchable plasmonic routers based on branched silver nanowires controlled by the polari­zation of the input light.

In a second approach the group proposed and studied a novel type of ultra-small plasmonic modulator based on a metal-isolator-metal wave­guide and a side-coupled magneto-optical disk controlled by an external magnetic field. The wave­number change and the trans­mission of surface-plasmon-polari­tons can be tuned by altering the magnetic field and reversible on/off switching of the running SPP modes by a reversal of the direction of the external magnetic field is demons­trated.

Resonant enhance­ment of the magneto-plasmonic modu­lation by more than 200 times leads to a modulation contrast ratio more than 90 % keeping a moderate insertion loss within an optical bandwidth of hundreds of GHz. Numerical simu­lations by the solution of Maxwell’s equations confirm the predic­tions by the derived analytical formulas of a high-contrast magneto-plasmonic modu­lation. As seen by changing the direction of the external magnetic field, the trans­mission of the SPPs is switched from an off to an on state via the changed inter­ference pattern in the waveguide. (Source: MBI)

Reference: K.-S. Ho et al.: Switchable plasmonic routers controlled by external magnetic fields by using magneto-plasmonic waveguides, Sci. Rep. 8, 10584 (2018); DOI: 10.1038/s41598-018-28567-8

Link: Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy, Berlin, Germany

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