Giant enhancement of the magneto-optical Kerr effect (MOKE) by surface plasmon polaritons (SPPs) is theoretically shown in a trilayer structure consisting of double-layer dielectrics and a ferromagnetic metal (Al2O3/SiO2/Fe). We calculated the resonant enhancement of the transverse MOKE (TMOKE) and polar MOKE (PMOKE) using the attenuated total reflection (ATR) configuration with the transfer matrix method using a 4 × 4 scattering matrix. At a specific film thickness of the low-index SiO2 layer, where confinement of the SPPs on the Fe surface becomes close to the cutoff condition, the incident light from the Al2O3 couples with the SPPs at the SiO2/Fe boundary most efficiently, resulting in resonant enhancement of the MOKE at an incident angle corresponding to the wave vector of the SPPs. The calculated PMOKE showed orthogonal transformation (90°-rotation) and almost full-orbed deformation (44°-ellipticity) of the polarization, and the TMOKE showed a change in reflectance of about 34 dB upon magnetization reversal.

Here, we show the high wavelength tunability and magnetic field modulation of surface plasmon polaritons (SPPs) of a waveguide mode that Double-layer Dielectrics and Ferromagnetic Metal, Al2O3/SiO2/Fe, trilayer structures exhibit when excited in the Otto configuration of attenuated total reflection setup. First by modeling, and then experimentally, we demonstrate that it is possible to tune the wavelength at which the angular dependent reflectance of these structures reaches its absolute minimum by simply adjusting the SiO2 intermediate dielectric layer thickness. This precise wavelength corresponds to the cut-off condition of SPPs' waveguide mode supported by the proposed structure, and it can be then switched between two values upon magnetization reversal of the Fe layer. In this specific situation, a large enhancement of the transverse magneto-optical effect is also obtained.

We report enhancement of the transverse magneto-optic Kerr effect (TMOKE) in Au/Fe/Au trilayers for improving the refractive index (RI) sensitivity in surface plasmon resonance sensors by magnetic modulation. The thicknesses of the upper Au layer, the Fe layer and the lower Au layer with required thickness resolution were theoretically optimized to maximize the TMOKE intensity with perfect momentum matching, and 3% TMOKE intensity was obtained in a trilayer. Furthermore, a wedge-shaped Au thin film was fabricated on a glass substrate, and the incident angle showing minimum reflectivity was modulated, corresponding to a difference in momentum matching. Resolution of the metal layer thickness (0.26 nm) was demonstrated in a single sensor chip for maximizing the TMOKE intensity. Enhanced RI resolution is expected in sensor chips formed of a Au/Fe/wedge Au trilayer, which will contribute to improvements in the limit of detection when measuring the analytes by analyzing the resulting signals.

We have implemented the nonreciprocal propagation capabilities into plasmonic waveguides and have simulated the performances. We employed dielectric-loaded surface plasmon polariton waveguide (DLSPPW) and long-range DLSPPW (LR-DLSPPW) configurations, where ferromagnetic-metal Fe is used instead of noble metals in order to obtain nonreciprocal propagations by the transverse magneto-optical (MO) effect. The nonreciprocal performances were characterized by the finite-difference frequency-domain (FDFD) method in terms of the propagation losses in return for the nonreciprocal phase shift (NRPS) and nonreciprocal propagation loss (NRL). The NRPS and NRL of the DLSPPW configuration are larger than those of the previously reported semiconductor waveguide optical isolators owing to the large MO constant of Fe and the field confinement by surface plasmons although the propagation loss for NRL of 1 dB is at least 31 dB and the propagation length is limited to less than 10 μm. To reduce such a large propagation loss, we introduced the LR-DLSPPW configuration composed of Polymethyl methacrylate (PMMA) ridge and Benzocyclobutene (BCB) buffer layer. The Fe layer thickness and width are optimized to 50 nm and 500 nm, respectively, so that sizable MO effect and low propagation loss coexist. The propagation loss for NRL of 1 dB is suppressed to ~10 dB within a waveguide length of ~56 μm. Our comprehensive investigation offers fundamental information on practical magneto-plasmonic waveguides and how much nonreciprocal performances are expected, providing an insight into the integration of magneto-plasmonics with on-chip photonics and electronics.

Al2O3/SiO2/Fe/Au structures with different Fe thicknesses were fabricated using different deposition techniques. Due to the cutoff condition of surface plasmon polaritons in the double-layer dielectric structure and magneto-optical effect, the reflectivity spectra show a minimum and its angular and wavelength positions can be modulated by the magnetic field. For thin Fe layers, the magnetic field modulates mainly the angular position, whereas for thick Fe layers both wavelength and angular positions are modulated. The proposed structure and the angular and wavelength dependence suggest two feasibilities of (1) two selectable interrogation modes: whereas for structures with thin Fe layers angular interrogation mode is preferred, with thick Fe layers wavelength interrogation mode is more appropriate, and (2) discrimination of analyte in the complex space: the refractive shift in the real part would dominantly appear in the angular interrogation, while the imaginary part in the wavelength interrogation.