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.

Magnetochiroptical nanocavities in hyperbolic metamaterials enable sensing down to the few-molecule level.

In this work, we combine the concepts of magnetic circular dichroism, nanocavities, and magneto-optical hyperbolic metamaterials (MO-HMMs) to demonstrate an approach for sensing down to a few molecules. Our proposal comprises a multilayer MO-HMM with a square, two-dimensional arrangement of nanocavities. The magnetization of the system is considered in polar configuration, i.e., in the plane of polarization and perpendicular to the plane of the multilayer structure. This allows for magneto-optical chirality to be induced through the polar magneto-optical Kerr effect, which is exhibited by reflected light from the nanostructure. Numerical analyses under the magnetization saturation condition indicate that magnetic circular dichroism peaks can be used instead of reflectance dips to monitor refractive index changes in the analyte region. Significantly, we obtained a relatively high sensitivity value of S = 40 nm/RIU for the case where refractive index changes are limited to the volume inside nanocavities, i.e., in the limit of a few molecules (or ultralow concentrations), while a very large sensitivity of S = 532 nm/RIU is calculated for the analyte region distributed along the entire superstrate layer.

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.

All-dielectric magnetophotonic gratings for maximum TMOKE enhancement.

All-dielectric nanophotonic devices are promising candidates for future lossless (bio)sensing and telecommunication applications. Active all-dielectric magnetophotonic devices, where the optical properties can be controlled by an externally applied magnetic field, have triggered great research interest. However, magneto-optical (MO) effects are still low for applications. Here, we demonstrate a concept for the enhancement of the transverse MO Kerr effect (TMOKE), with amplitudes of up to 1.85, i.e., close to the maximum theoretical values of ±2 (in transmission). Our concept exploits the lateral leaky Bloch-modes to enhance the TMOKE, under near-zero transmittance conditions. Potential applications in (bio)sensing structures are numerically demonstrated. The effects of optical losses were studied using different combinations of materials. Significantly, we demonstrate TMOKE enhancements of two orders of magnitude in relation to recent experimental studies, using the same building materials.

Magneto-optical micro-ring resonators for dynamic tuning of add/drop channels in dense wavelength division multiplexing applications.

We numerically demonstrate an all-dielectric approach for magnetically tunable add/drop of optical channels in dense wavelength division multiplexing applications. Our concept comprises a micro-ring resonator, with an inner magneto-optical disk, side-coupled to two waveguides. The simulation results, obtained within the ITU-T G.694.1 recommendation, indicate high performance add/drop of odd and even optical channels (along the entire C-band) by flipping the intrinsic magnetization of the disk. Since the simulations were performed with CMOS-compatible materials, it is hoped that the structure proposed here can be integrated into future ultrafast optical communication networks.

Toward Lossless Infrared Optical Trapping of Small Nanoparticles Using Nonradiative Anapole Modes.

A challenge in plasmonic trapping of small nanoparticles is the heating due to the Joule effect of metallic components. This heating can be avoided with electromagnetic field confinement in high-refractive-index materials, but nanoparticle trapping is difficult because the electromagnetic fields are mostly confined inside the dielectric nanostructures. Herein, we present the design of an all-dielectric platform to capture small dielectric nanoparticles without heating the nanostructure. It consists of a Si nanodisk engineered to exhibit the second-order anapole mode at the infrared regime (λ=980 nm), where Si has negligible losses, with a slot at the center. A strong electromagnetic hot spot is created, thus allowing us to capture nanoparticles as small as 20 nm. The numerical calculations indicate that optical trapping in these all-dielectric nanostructures occurs without heating only in the infrared, since for visible wavelengths the heating levels are similar to those in plasmonic nanostructures.

Erratum: Toward Lossless Infrared Optical Trapping of Small Nanoparticles Using Nonradiative Anapole Modes [Phys. Rev. Lett. 127, 186803 (2021)].

This corrects the article DOI: 10.1103/PhysRevLett.127.186803.

Plasmonic Biosensing.

Plasmonic biosensing has been used for fast, real-time, and label-free probing of biologically relevant analytes, where the main challenges are to detect small molecules at ultralow concentrations and produce compact devices for point-of-care (PoC) analysis. This review discusses the most recent, or even emerging, trends in plasmonic biosensing, with novel platforms which exploit unique physicochemical properties and versatility of new materials. In addition to the well-established use of localized surface plasmon resonance (LSPR), three major areas have been identified in these new trends: chiral plasmonics, magnetoplasmonics, and quantum plasmonics. In describing the recent advances, emphasis is placed on the design and manufacture of portable devices working with low loss in different frequency ranges, from the infrared to the visible.

Refractive index of ZnO ultrathin films alternated with Al2O3 in multilayer heterostructures.

The design of optoelectronic devices made with ZnO superlattices requires the knowledge of the refractive index, which currently can be done only for films thicker than 30 nm. In this work, we present an effective medium approach to determine the refractive index of ZnO layers as thin as 2 nm. The approach was implemented by determining the refractive index of ZnO layers ranging from 2 nm to 20 nm using spectroscopic ellipsometry measurements in multilayers. For a precise control of morphology and thickness, the superlattices were fabricated with atomic layer deposition (ALD) with alternating layers of 2 nm thick Al2O3 and ZnO, labeled as N ZnO-Al2O3, where N = 10, 20, 30, 50, 75 and 100. The total thickness of all superlattices was kept at 100 nm. The approach was validated by applying it to similar superlattices reported in the literature and fitting the transmittance spectra of the superlattices.

Surface Plasmon Resonances in Sierpinski-Like Photonic Crystal Fibers: Polarization Filters and Sensing Applications.

We investigate the plasmonic behavior of a fractal photonic crystal fiber, with Sierpinski-like circular cross-section, and its potential applications for refractive index sensing and multiband polarization filters. Numerical results were obtained using the finite element method through the commercial software COMSOL Multiphysics®. A set of 34 surface plasmon resonances was identified in the wavelength range from λ=630 nm to λ=1700 nm. Subsets of close resonances were noted as a consequence of similar symmetries of the surface plasmon resonance (SPR) modes. Polarization filtering capabilities are numerically shown in the telecommunication windows from the O-band to the L-band. In the case of refractive index sensing, we used the wavelength interrogation method in the wavelength range from λ=670 nm to λ=790 nm, where the system exhibited a sensitivity of S(λ)=1951.43 nm/RIU (refractive index unit). Due to the broadband capabilities of our concept, we expect that it will be useful to develop future ultra-wide band optical communication infrastructures, which are urgent to meet the ever-increasing demand for bandwidth-hungry devices.

Surface plasmon resonance biosensor for enzymatic detection of small analytes.

Surface plasmon resonance (SPR) biosensing is based on the detection of small changes in the refractive index on a gold surface modified with molecular recognition materials, thus being mostly limited to detecting large molecules. In this paper, we report on a SPR biosensing platform suitable to detect small molecules by making use of the mediator-type enzyme microperoxidase-11 (MP11) in layer-by-layer films. By depositing a top layer of glucose oxidase or uricase, we were able to detect glucose or uric acid with limits of detection of 3.4 and 0.27 µmol l-1, respectively. Measurable SPR signals could be achieved because of the changes in polarizability of MP11, as it is oxidized upon interaction with the analyte. Confirmation of this hypothesis was obtained with finite difference time domain simulations, which also allowed us to discard the possible effects from film roughness changes observed in atomic force microscopy images. The main advantage of this mediator-type enzyme approach is in the simplicity of the experimental method that does not require an external potential, unlike similar approaches for SPR biosensing of small molecules. The detection limits reported here were achieved without optimizing the film architecture, and therefore the performance can in principle be further enhanced, while the proposed SPR platform may be extended to any system where hydrogen peroxide is generated in enzymatic reactions.

Bulk plasmon-polariton gap solitons in defective metamaterial photonic superlattices.

We show the existence of a defect mode within the plasmon-polariton gap in 1D defective photonic superlattices, composed by alternating layers of conventional dielectric (A) and negative refractive (B) material slabs with a dielectric defective layer (D), which, in the nonlinear regime, can be tuned by means of the incident field intensity. Also, we have shown that the self-induced transparency phenomena can be only observed when gap-soliton modes, coupled through the defective layer, are excited in both mirror systems around the defective slab.

Simultaneous omnidirectional zero-n¯ and zero-ϕeff non-Bragg gaps in metamaterial-polaritonic photonic superlattices.

Present study shows that the inclusion of single negative polaritonic-like layers in one-dimensional metamaterial photonic superlattices may lead to new effects, such as the simultaneous existence of omnidirectional zero-n¯ and zero-ϕ(eff) non-Bragg gaps for both transversal electric (TE) and transversal magnetic (TM) polarizations, which are also robust to uniaxial anisotropic effects. Such omnidirectional behavior, in the case of the zero-n¯ gap, occurs within the same frequency range for both polarizations, which is not allowed in the case of double negative (DNG) metamaterial-air superlattices, suggesting a route to design and development of omnidirectional optical filters for all polarizations. Furthermore, present results show that, when polaritonic inclusions are considered, the long wavelength approximation is not ever suitable to describe the non-Bragg gap edges.

Coupling-barrier and non-parabolicity effects on the conduction electron cyclotron effective mass and Landé [Formula: see text] factor in GaAs double quantum wells.

We have performed a theoretical study of the effects of the non-parabolicity and coupling barrier in between GaAs quantum wells on the conduction electron cyclotron effective mass and Landé [Formula: see text] factor under the action of a growth-direction applied magnetic field. Numerical calculations are performed within the effective mass approximation and taking into account the non-parabolicity effects for the conduction-band electrons, by means of the Ogg-McCombe effective Hamiltonian. The system consists of two GaAs quantum wells connected by a Ga(1 - x)Al(x)As barrier and surrounded by Ga(1 - y)Al(y)As material. We have found that both the [Formula: see text] factor and the cyclotron effective mass are sensitive to the coupling strength, that is the height and width of the barrier in between the GaAs quantum wells. This behavior is similar for every Landé [Formula: see text] factor and the cyclotron effective mass calculated for different Landau levels. It is noticeable that the splitting between the [Formula: see text] and [Formula: see text] cyclotron effective mass increases with the central barrier width and the growth-direction applied magnetic field. As in a single quantum well, we found that the electron Landé [Formula: see text] factor increases with the growth-direction applied magnetic field, comparing quite well with the experimental reports, and that the magnetic field plays an important role in decoupling the quantum wells of the system. Additionally, we have studied the electron cyclotron effective mass and Landé g factor as functions of the Landau levels, depending on the non-parabolicity. From this result one can infer that their population must be taken into account for a complete study of the band parameters as has been proposed in previous works. The present theoretical results are in very good agreement with previous experimental reports in the limiting geometry of a single quantum well.

Enhanced Transverse Magneto-Optical Kerr Effect in Magnetoplasmonic Crystals for the Design of Highly Sensitive Plasmonic (Bio)sensing Platforms.

We propose a highly sensitive sensor based on enhancing the transversal magneto-optical Kerr effect (TMOKE) through excitation of surface plasmon resonances in a novel and simple architecture, which consists of a metal grating on a metal magneto-optical layer. Detection of the change in the refractive index of the analyte medium is made by monitoring the angular shift of the Fano-like resonances associated with TMOKE. A higher resolution is obtained with this technique than with reflectance curves. The key aspect of the novel architecture is to achieve excitation of surface plasmon resonances mainly localized at the sensing layer, where interaction with the analyte occurs. This led to a high sensitivity, S = 190° RIU-1, and high performance with a figure of merit of the order of 103, which can be exploited in sensors and biosensors.

Zero-(n) non-Bragg gap plasmon-polariton modes and omni-reflectance in 1D metamaterial photonic superlattices.

A theoretical study of the photonic band structure and transmission spectra for 1D periodic superlattices with an elementary cell composed of two layers of refractive indices n(a) and n(b), which may take on positive as well as negative values, has been performed within the transfer-matrix approach. The dependence on the angle of incidence of the electromagnetic wave for excitation of plasmon-polaritons as well as the properties of the (n) = 0 gap were thoroughly investigated. Results are found for the generalized conditions that must be satisfied by the ratio a/b of the layer widths of metamaterial photonic superlattices, for both transverse electric and transverse magnetic polarizations, in order to have an omnidirectional (n) = 0 gap. The present study indicates new perspectives in the design and development of future optical devices.

Quantum confinement and magnetic-field effects on the electron g factor in GaAs-(Ga, Al)As cylindrical quantum dots.

We have performed a theoretical study of the quantum confinement (geometrical and barrier potential confinements) and axis-parallel applied magnetic-field effects on the conduction-electron effective Landé g factor in GaAs-(Ga, Al)As cylindrical quantum dots. Numerical calculations of the g factor are performed by using the Ogg-McCombe effective Hamiltonian-which includes non-parabolicity and anisotropy effects-for the conduction-band electrons. The quantum dot is assumed to consist of a finite-length cylinder of GaAs surrounded by a Ga(1-x)Al(x)As barrier. Theoretical results are given as functions of the Al concentration in the Ga(1-x)Al(x)As barrier, radius, lengths and applied magnetic fields. We have studied the competition between the quantum confinement and applied magnetic field, finding that in this type of heterostructure the geometrical confinement and Al concentration determine the behavior of the electron effective Landé [Formula: see text] factor, as compared to the effect of the applied magnetic field. Present theoretical results are in good agreement with experimental reports in the limiting geometry of a quantum well, and with previous theoretical findings in the limiting case of a quantum well wire.