A new type of third-order nonlinearity in magneto-plasmonic structures

The study of nonlinear phenomena in magneto-plasmonic waveguides is of great interest, not only for their fundamental importance, but also for potential applications in integrated nano-optical systems for information processing. Recently, Dr. Joachim Herrmann (MBI) in collaboration with foreign cooperation partners predicted a new type of ultrafast third-order nonlinearity of surface plasmon polaritons (SPP) in planar magneto-plasmonic structures, based on the inverse Faraday effect. In particular, the research group shows that SPPs with a longitudinal component of the electric field in a thin magnetic layer can generate a transverse magnetic field by the inverse Faraday effect (IFE), and the effect of this effect on plasmon propagation to ultrafast third order nonlinearity leads. The susceptibility of the new nonlinearity exceeds that of the optical Kerr effect of typical dielectric materials by five orders of magnitude and that of gold by two orders of magnitude.

In a magnetic material irradiated with circularly polarized light, magnetization is generated along the wave vector. This phenomenon is called Inverse Faraday Effect (IFE). The sign of the light-induced magnetization is determined by the helicity of the incident light, and the magnetization disappears for linearly polarized light. Left- and right-polarized light induces magnetization of opposite sign.

Fig. 1: Diagram of a ferromagnetic dielectric / metallic boundary layer.

While light does not penetrate into a thin metallic layer, under suitable conditions surface plasmon polaritons can be excited, which have long since spread to the surface. Since SPPs have a longitudinal component of the electric field, even linearly polarized incident light can generate magnetization by the plasmons that are excited by the incident light. However, the plasmons are not circularly polarized in the conventional sense.

Fig. 2: Dependence of the IFE-related nonlinear susceptibility on the wavelength for a boundary layer between gold and a ferromagnetic dielectric material.

To quantify this new type of nonlinearity, the group derived an analytical formula for the IFE-related nonlinear susceptibility of planar magneto-plasmonic structures using the Lorentz reciprocity theorem. The new IFE-related nonlinearity plays an analogous role in the SPP propagation as the optical Kerr effect; however, it arises from a different physical mechanism and differs from that of the optical Kerr effect by its magnitude, its frequency dependence, and its dependence on material parameters.

Fig. 3: Dependence of the non-linear phase shift on the power at a wavelength of 1550 nm and a propagation length of 1000 nm.

The scheme of a ferromagnetic dielectric / metallic interface is shown in Fig.1. The dependence of the nonlinear propagation coefficient on the wavelength can be seen in Fig.2 and the dependence of the nonlinear phase shift on the power in Fig.3.

Magneto-plasmonic structures open the possibility for a new class of nano-optical elements that are important for key applications in nanoinformation technology. These results can lead to promising and important applications in this area.

Original publication

Third-order nonlinearity by the inverse Faraday effect in planar magnetoplasmonic structures

S.-J. Im, C.-S. Ri, K.-S. Ho, J. Herrmann

Physical Review B 96 (2017)