Magnetic-field modulation of surface plasmon polaritons on gratings

Magnetically controllable metasurface and its application

The dynamic control of the metasurface opens up a vital technological approach for the development of multifunctional integrated optical devices. The magnetic field manipulation has the advantages of sub-nanosecond ultra-fast response, non-contact, and continuous adjustment. Thus, the magnetically controllable metasurface has attracted significant attention in recent years. This study introduces the basic principles of the Faraday and Kerr effect of magneto-optical (MO) materials. It classifies the typical MO materials according to their properties. It also summarizes the physical mechanism of different MO metasurfaces that combine the MO effect with plasmonic or dielectric resonance. Besides, their applications in the nonreciprocal device and MO sensing are demonstrated. The future perspectives and challenges of the research on MO metasurfaces are discussed.

Enhanced Faraday rotation by dielectric metasurfaces with Bayesian shape-optimized scatterers

In this Letter, we demonstrate how to optimize the magneto-optic response of a Huygens metasurface composed of square arrays of all-dielectric nano-disk scatterers. We compare cylindrical and shape-modified disks. Both provide a strongly enhanced Faraday rotation that is accompanied by almost 100% transmittance. The shape modification obtained via a Bayesian optimization algorithm results in a 50% increase in the magneto-optic response compared to the best cylindrical disk, providing 15° of polarization rotation for a 260 nm thick metasurface.

High-performance sensor achieved by hybrid guide-mode resonance/surface plasmon resonance platform

We perform a comprehensive analysis of multiband absorption properties in a metal-dielectric-metal-dielectric (MDMD) nanostructure under TM wave illumination. The multiband absorption can be attributed to the hybridization of the surface plasmon resonance (SPR) and the guide-mode resonance (GMR), and we identify the hybrid GMR/SPR by the dispersion relation equations of the SPR and GMR, respectively. More importantly, the MDMD nanostructure is very sensitive to the change of the dielectric environment for the special hybrid structure; thus, it can function as a good candidate for ultrasensitive biochemical sensing. The highest sensitivity of the MDMD nanostructure reaches 1087 nm/RIU with the figure of merit (FoM) of 23 and the new figure of merit (FoM^*) of 483; it is performed by the absorption peak at 1796.1 nm of the double surface plasmon polariton with the strongest field enhancement at the surface.

Transverse magneto-optical Kerr effect in active magneto-plasmonic structures

We propose a novel method to enhance the transverse magneto-optical Kerr effect (TMOKE) in the magneto-plasmonic (MP) nanostructures by means of the active dielectric layer. We report the theoretical analysis of the MP structure with a ferromagnetic dielectric doped with rear-earth ions (Nd³⁺) as the example of a gain layer. The enhancement takes place near the surface plasmon polariton (SPP) resonances of the nanostructures. The stimulated emission of the dopants in the field of the SPP wave partially compensates its losses. It is shown that due to a decrease of SPP damping, a Q-factor of the MP resonance increases and the TMOKE is increased in comparison with the passive nanostructure.

Linear mode conversion of terahertz radiation into terahertz surface magnetoplasmons on a rippled surface of magnetized n-InSb

A new mechanics of linear mode conversion of terahertz (THz) radiation into THz surface magnetoplasmons on a rippled surface of magnetized n-InSb is proposed. The normally incident THz radiation, polarized in the direction of a ripple wave vector, imparts oscillatory velocity to electrons in the ripple layer. This velocity beats with surface ripple to produce a nonlinear current that resonantly drives the THz surface magnetoplasmons. In the presence of an applied magnetic field, the surface plasmon (SP) mode splits into two modes-an upper mode and a lower mode. The amplitude of the SP for the upper branch mode is higher than that for the lower mode.

Plasmon-mediated magneto-optical transparency

Magnetic field control of light is among the most intriguing methods for modulation of light intensity and polarization on sub-nanosecond timescales. The implementation in nanostructured hybrid materials provides a remarkable increase of magneto-optical effects. However, so far only the enhancement of already known effects has been demonstrated in such materials. Here we postulate a novel magneto-optical phenomenon that originates solely from suitably designed nanostructured metal-dielectric material, the so-called magneto-plasmonic crystal. In this material, an incident light excites coupled plasmonic oscillations and a waveguide mode. An in-plane magnetic field allows excitation of an orthogonally polarized waveguide mode that modifies optical spectrum of the magneto-plasmonic crystal and increases its transparency. The experimentally achieved light intensity modulation reaches 24%. As the effect can potentially exceed 100%, it may have great importance for applied nanophotonics. Further, the effect allows manipulating and exciting waveguide modes by a magnetic field and light of proper polarization.

Magneto-optical effects, where magnetic fields affect light propagating through a material, are of interest for photonic devices such as switches. The magneto-optical effect discovered here in metal-dielectric nanostructures shows a strong light modulation that is suitable for nanophotonic applications.

Magnetic modulation of surface plasmon modes in magnetoplasmonic metal-insulator-metal cavities

The magnetic modulation of the surface plasmon-polariton (SPP) wavevector is experimentally and theoretically studied for the plasmonic modes excited in metal-insulator-metal (MIM) magnetoplasmonic cavities. For this purpose, Ag/SiO₂/Ag multilayers with different SiO₂ layer thickness in which a thin Co layer is positioned near the top Ag/SiO₂ interface, near the bottom SiO₂/Ag one, or near both of them, are studied. The magnetoplasmonic MIM cavities present symmetric (SM) and antisymmetric (AM) plasmonic modes, of different wavevector and electromagnetic field profiles inside the MIM cavity. We show that the magnetic SPP wavevector modulation strongly depends on which mode is considered, the cavity thickness, and the number and specific location of Co layers within the structure. With only one ferromagnetic layer, a net modulation is obtained, of higher magnitude as we reduce the SiO₂ layer thickness. The introduction of a second Co layer in the structure reduces the modulation due to the non-reciprocal character of SPP modes under an applied magnetic field. Moreover, we demonstrate that the non-reciprocal nature of the SPP modulation can be experimentally visualized in the magnetic hysteresis loops under plasmon excitation conditions by using two Co layers with different magnetization switching fields.

Low-temperature plasmonics of metallic nanostructures

The requirements for spatial and temporal manipulation of electromagnetic fields on the nanoscale have recently resulted in an ever-increasing use of plasmonics for achieving various functionalities with superior performance to those available from conventional photonics. For these applications, ohmic losses resulting from free-electron scattering in the metal is one major limitation for the performance of plasmonic structures. In the low-frequency regime, ohmic losses can be reduced at low temperatures. In this work, we study the effect of temperature on the optical response of different plasmonic nanostructures and show that the extinction of a plasmonic nanorod metamaterial can be efficiently controlled with temperature with transmission changes by nearly a factor of 10 between room and liquid nitrogen temperatures, while temperature effects in plasmonic crystals are relatively weak (transmission changes only up to 20%). Because of the different nature of the plasmonic interactions in these types of plasmonic nanostructures, drastically differing responses (increased or decreased extinction) to temperature change were observed despite identical variations of the metal's permittivity.

Optical and magneto-optical resonances in nanocorrugated ferromagnetic films

We report here on optical and magneto-optical spectra investigations of nanostructured Co and Ni films deposited on top of polymethyl methacrylate (PMMA) colloidal crystal. Resonant peculiarities have been observed in both spectra; their positions are scaled with the PMMA sphere diameter and depend on incident angle. Asymmetry of the resonance lineshapes as well as change of the direction of magneto-optical rotation has been observed. Both the surface plasmon resonance and the interference between reflections from the colloidal crystal and from the nanostructured film should be considered to explain the obtained results.

Highly efficient all-optical control of surface-plasmon-polariton generation based on a compact asymmetric single slit

By engaging a compact asymmetric single slit coated with a photorefractive polymer, surface-plasmon-polariton (SPP) generation was efficiently controlled by a pump beam. In the structure, the nonlinear light-matter interaction is enhanced because of the cavity effect, which increases the sensitivity of SPPs to the surrounding dielectric. By variation of the real part of the refractive index together with an interferometric configuration, high on/off switching ratios are achieved. Moreover, the SPP generation and modulation processes are integrated in the same asymmetric single slit, which makes the device ultracompact. Experimentally, a high on/off switching ratio of >20 dB and phase variation of >π were observed with the device lateral dimension of only about 2 μm.

Enhanced magneto-optical effects in magnetoplasmonic crystals

Plasmonics allows light to be localized on length scales much shorter than its wavelength, which makes it possible to integrate photonics and electronics on the nanoscale. Magneto-optical materials are appealing for applications in plasmonics because they open up the possibility of using external magnetic fields in plasmonic devices. Here, we fabricate a new magneto-optical material, a magnetoplasmonic crystal, that consists of a nanostructured noble-metal film on top of a ferromagnetic dielectric, and we demonstrate an enhanced Kerr effect with this material. Such magnetoplasmonic crystals could have applications in telecommunications, magnetic field sensing and all-optical magnetic data storage.

Plasmonics and enhanced magneto-optics in core-shell co-ag nanoparticles

We present theoretical and experimental studies that explain the observed strong enhancement of the magneto-optical (MO) Faraday rotation in all-metal core-shell Co-Ag nanoparticles (NPs) attributed to localized surface plasmon resonance (LSPR). We also explain why the optical absorption and MO spectra peaks appear blue-shifted with increased Co core size while keeping the NP size constant. Further, we demonstrate direct correlation between the strong LSPR induced electromagnetic fields and the enhanced MO activity of the NPs.