• Chinese Optics Letters
  • Vol. 19, Issue 8, 083602 (2021)
Vahid Foroughi Nezhad1、2, Chenglong You3, and Georgios Veronis1、2、*
Author Affiliations
  • 1School of Electrical Engineering and Computer Science, Louisiana State University, Baton Rouge, Louisiana 70803, USA
  • 2Center for Computation and Technology, Louisiana State University, Baton Rouge, Louisiana 70803, USA
  • 3Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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    We introduce a nanoplasmonic isolator that consists of a cylindrical resonator placed close to a metal-dielectric-metal (MDM) waveguide. The material filling the waveguide and resonator is a magneto-optical (MO) material, and the structure is under an externally applied static magnetic field. We theoretically investigate the properties of the structure and show that the cavity mode without MO activity splits into two modes when the MO activity is present. In addition, we find that the presence of the MDM waveguide leads to a second resonance due to the geometrical asymmetry caused by the existence of the waveguide. We also show that, when MO activity is present, the cavity becomes a traveling wave resonator. Thus, the transmission of the structure depends on the direction of the incident light, and the proposed structure operates as an optical isolator.

    1. Introduction

    Nonreciprocal elements such as circulators and isolators are essential for the realization of integrated optical circuits[1]. The design of nonreciprocal components requires breaking the time reversal symmetry[2,3]. This can be achieved through the use of nonlinear materials[4,5], materials with time-dependent properties[6], and magneto-optical (MO) materials[7]. However, since the MO response of natural materials is weak at optical wavelengths, designing nonreciprocal devices that are based on MO materials results in bulky structures that are much larger than the wavelength[8]. The advent of silicon photonics and photonic crystals has reduced the size of nonreciprocal optical components down to wavelength scale[912]. To further decrease the size down to the subwavelength scale, one needs to beat the diffraction limit. Nanoscale metallic structures that support surface plasmon polaritons can be used to achieve subwavelength scale optical components, because they can beat the diffraction limit[13,14]. Combining metallic and MO materials can therefore pave the way for highly compact nonreciprocal plasmonic elements[1522]. One of the promising ways to engineer integrated plasmonic circuits is to employ metal-dielectric-metal (MDM) waveguides[23]. Several different nanoscale plasmonic components based on MDM waveguides have been proposed, including filters[24,25], couplers[26,27], sensors[2830], switches[3135], and rectifiers[36].