Design of Nanoarchitectures for Magnetoplasmonic Biosensing with Near-Zero-Transmittance Conditions

Broadband Enhancement of Magneto-Optical Effects in Hybrid Waveguide-Plasmonic Surfaces for Sensing

Conventional magnetophotonic nanostructures typically function within narrow wavelength and incident angle ranges, where resonance is observed and magneto-optical (MO) effects are amplified. Expanding these operational ranges may allow for improved applications, including in (bio)sensing devices. In this study, we describe a hybrid magnetoplasmonic waveguide grating (HMPWG) in which the coupling of plasmonic resonances and waveguide modes leads to enhanced MO effects and sensitivity, according to full-wave electromagnetic simulations. High transverse magneto-optical Kerr effect (TMOKE) signals were observed for the full range of wavelengths and angles investigated, i.e., for θinc ≥ 1° and 500 nm ≤ λ ≤ 850 nm. As a proof-of-concept we verified that using the HMPWG nanostructure with an aqueous solution as superstrate one may obtain a sensitivity in variation of the refractive index unit (RIU) of S = 166°/RIU and S = 230 nm/RIU in angle and wavelength interrogation modes, respectively. Upon comparing with conventional magnetoplasmonic gratings, which only enable excitation of plasmonic resonances, we demonstrate that HMPWG nanostructures can be further optimized to reach not only high sensitivity but also high resolution in sensing and biosensing.

Magnetically tunable Brewster angle in uniaxial magneto-optical metamaterials for advanced integration of high-resolution sensing devices

In this Letter, we introduce a concept to produce high-resolution, highly integrable biosensing devices. Our idea exploits the highly absorbing modes in multilayered metamaterials to maximize the transverse magneto-optical Kerr effect (TMOKE). Results are discussed in the context of dielectric uniaxial (ε eff,∥ ε eff,⊥>0) and hyperbolic metamaterial (ε eff,∥ ε eff,⊥<0) regimes. For applications in gas sensing, we obtained sensitivities of S = 46.02 deg/RIU and S = 73.91 deg/RIU when considering the system working in the uniaxial and hyperbolic regimes, respectively, with figures of merit (resolution) in the order of 310 or higher. On the contrary, when considering the system for biosensing applications (incidence from an aqueous medium), we observed that the proposed mechanism can only be successfully used in the uniaxial regime, where a sensitivity of 56.87 deg/RIU was obtained.

Ferromagnetic Subwavelength Periodic Nanogroove Structure with High Magneto-Optical Kerr Effect for Sensing Applications

The transverse magneto-optical Kerr effect (TMOKE) with gas sensing ability was comprehensively investigated in this study by directly patterning a subwavelength periodic nanogroove on a cobalt film. High-amplitude TMOKE was observed for the proposed structure, which was 243 times as intense as that of a smooth film. Further, the physical mechanism responsible for this significant improvement is elucidated by the effective activation of surface plasmon resonance at the gas-cobalt interface. The mechanism was established by investigating the electric field distributions at a resonant angle of incidence and the reflectance spectra associated with the metallic nanogroove grating structure. Moreover, we demonstrate that this scheme has a high detection sensitivity of up to 112.2° per refractive index unit and a large figure of merit, allowing the system to be integrated with microfluidics for sensing applications.

Enhanced transverse magneto-optical Kerr effect using ferromagnetic metal perforated with nanopore arrays

Enhancement of transverse magneto-optical Kerr effects (T-MOKEs) based on surface plasmon resonance has attracted wide attention because of their high sensing performance. Most studies, however, mainly focus on prism-based magnetoplasmonic structures or architectures that incorporate a noble metal lattice and ferromagnetic layer, hindering device fabrication, miniaturization, and integration into a microfluidic sensing configuration. Herein, we propose a single Co₆Ag₉₄ ferromagnetic-metal layer perforated with a square nanopore array system with a pronounced T-MOKE magnitude 51 times higher than that of a smooth film, and with potential to detect gaseous analytes. The proposed system is sufficient to detect gaseous media for early environmental monitoring and enables an accessible pathway for magneto-optical sensor design.

Magnetoplasmonic Nanoantennas for On-Chip Reconfigurable Optical Wireless Communications

On-chip wireless communications require optical nanoantennas with dynamically tunable radiation patterns, which may allow for higher integration with multiple nanoantennas instead of two fixed nanoantennas in existing approaches. In this paper, we introduce a concept to enable active manipulation of radiated beam steering using applied magnetic fields. The proposed system consists of a highly directive Yagi-Uda-like arrangement of magnetoplasmonic nanoribs made of Co₆Ag₉₄ and immersed in SiO₂. Numerical demonstration of the tilting of the radiated beam from the nanoantenna on its plane is provided with full-wave electromagnetic simulations using the finite element method. The tilt direction of the radiated beam can be changed by reversing the magnetization direction, while the conventional plasmonic nanoantenna pattern is recovered by demagnetizing the system. The geometry of the nanoantenna can be tailored to work at optical or infrared wavelengths, but a proof of concept for λ = 700 nm is conducted for taking advantage of the high magneto-optical activity of Co₆Ag₉₄. The design was based on experimental data for materials that can be fabricated via nanolithography, thus permitting magnetically on-chip reconfigurable optical wireless communications.

Active manipulation of radiated fields by a magnetoplasmonic half-wave dipole nanoantenna

We demonstrate a concept for the active manipulation of radiated fields by a magnetoplasmonic half-wave dipole nanoantenna. Our idea comprises a two arms nanoantenna, made of metallic ferromagnetic cobalt-silver alloy (Co₆Ag₉₄), inspired by the analogous radio frequency half-wave dipole antenna design. Numerical results, obtained under the magnetization saturation condition, indicate a tilting of the radiated beam depending on the magnitude and sense of the magnetization of the ferromagnetic material. Significantly, we obtained tilting angles as large as ±9.7^∘ around the y axis for the magnetization placed along the x or z axes, respectively. Results in this work not only open up a new, to the best of our knowledge, way to dynamically manipulate the beam steering at the chip-scale, but also contribute to unveil novel magneto-optical effects at the nanoscale.

Bulk Plasmon Polariton Modes in Hyperbolic Metamaterials for Giant Enhancement of the Transverse Magneto-Optical Kerr Effect

We demonstrate a concept for the giant enhancement of the transverse magneto-optical Kerr effect (TMOKE) using bulk plasmon polariton (BPP) modes in non-magnetic multilayer hyperbolic metamaterials (HMMs). Since the BPP modes are excited through the attenuated total reflection (ATR) mechanism, using a Si-based prism-coupler, we considered a single dielectric magneto-optical (MO) spacer between the prism and the HMM. The working wavelength was estimated, using the effective medium approach for a semi-infinite dielectric-plasmonic multilayer, considering the region where the system exhibits type II HMM dispersion relations. Analytical results, by means of the scattering matrix method (SMM), were used to explain the physical principle behind our concept. Numerical results for giant TMOKE values (close to their maximum theoretical values, ±1) were obtained using the finite element method (FEM), applying the commercial software COMSOL Multiphysics. Our proposal comprises a simple and experimentally feasible structure that enables the study of MO phenomena in HMMs, which may find application in future nanostructured magnetoplasmonic metamaterials for active nanophotonic devices.

Optimization of Magnetoplasmonic ε-Near-Zero Nanostructures Using a Genetic Algorithm

Magnetoplasmonic permittivity-near-zero (ε-near-zero) nanostructures hold promise for novel highly integrated (bio)sensing devices. These platforms merge the high-resolution sensing from the magnetoplasmonic approach with the ε-near-zero-based light-to-plasmon coupling (instead of conventional gratings or bulky prism couplers), providing a way for sensing devices with higher miniaturization levels. However, the applications are mostly hindered by tedious and time-consuming numerical analyses, due to the lack of an analytical relation for the phase-matching condition. There is, therefore, a need to develop mechanisms that enable the exploitation of magnetoplasmonic ε-near-zero nanostructures' capabilities. In this work, we developed a genetic algorithm (GA) for the rapid design (in a few minutes) of magnetoplasmonic nanostructures with optimized TMOKE (transverse magneto-optical Kerr effect) signals and magnetoplasmonic sensing. Importantly, to illustrate the power and simplicity of our approach, we designed a magnetoplasmonic ε-near-zero sensing platform with a sensitivity higher than 56∘/RIU and a figure of merit in the order of 102. These last results, higher than any previous magnetoplasmonic ε-near-zero sensing approach, were obtained by the GA intelligent program in times ranging from 2 to 5 min (using a simple inexpensive dual-core CPU computer).