Magneto-biplasmonic slot waveguide isolator

Optical transmission non-reciprocity requires a propagation medium that simultaneously offers time and spatial symmetry breaking [1] . In the quest for integrated optical isolator, different physical mechanisms have been proposed, explored and improved to attain time-reversal breaking such as magneto-optics (MO) [2] , optical nonlinear methods [3] , dynamic modulation [4] or optomechanical interactions [5] . Transverse Magneto-Optical Kerr Effect (TMOKE) has appeared as the most relevant non-reciprocal effect to be used in guided configurations, enabling either non-reciprocal intensity transmission [6] or non-reciprocal phase shift in interferometric or resonant structures [2] . Very recently, another TMOKE based mechanism has been explored by the authors, which induces asymmetrisation of guided modes in MO slot waveguides [7] , [8] : the combination of magneto-plasmonic and coupled modes in this mechanism, is called "magneto-biplasmonic" effect. Due to this phenomena, the light propagates mainly on one side of the slot waveguide in forward direction, and along the other side in backward direction ( Fig. 1 ). By inserting absorbers on only one side, isolation function is obtained. The slot waveguide is a gold-BIG-gold structure, where BIG is a MO garnet. Since the asymmetrisation operates on the long-range (LR) or short-range (SR) surface plasmon polariton (SPP) coupled modes, the isolating structure must be interfaced with a single TE mode waveguide to realize full integration and selectively excite only the LRSPP mode ( Fig. 2 ).