Integrated magneto-plasmonic nanostructures

Non-reciprocal (NR) transmission in optical systems could considerably enrich possible architectures of integrated photonic circuits by enabling isolator or circulator functions to be exploited. The design of optical guided structure with NR functionality requires simultaneous spatial and time-reversal symmetry breakings in the waveguide. For magneto-optical (MO) materials, the presence of a static magnetic field, inducing magnetization, breaks timereversal symmetry. Such materials can be garnet-type oxides like Bi3Fe5O12 or ferromagnetic metals like FeCo. The most common optical isolators rely on the Faraday effect in bulk free space. MO garnet gives rise to polarization rotation, which has opposite signs for backward and forward propagation. Such configuration is difficult to integrate in photonics circuit because it needs two polarizers and a non-birefringent waveguide. For integrated optics, TMOKE (Transverse Magneto-optical Kerr Effect) appears more suitable, since it doesn’t depend on polarization conversion. Miniaturization of devices and improvement of performance requires a strong enhancement of NR effects, which can be obtained by exploiting plasmonic effects: the concentration of electromagnetic energy in nanoscale volume thanks to surface plasmon polaritons (SPPs) can lead to a strong exaltation of the MO effects. Among several disruptive behaviours, we can mention the huge enhancement of TMOKE non-reciprocal dichroism obtained with a metallic grating on a transparent MO substrate, or the sign inversion of the NR dichroism induced by FeCo Bragg grating on a waveguide or by gold grating on bismuth iron garnet (BIG) layer on a substrate for a given magnetization direction and by only grating shape modification.