Magneto-optical Layer Research Articles

Tuning the Photonic Spectrum of Superlattice Structures with Magnetic Fields: An Anisotropic Perspective

We investigate how an external magnetic field with an arbitrary direction affects the photonic band of a superlattice structure composed of alternating dielectric and magneto-optical plasma layers. By considering that the superlattice is electrodynamically anisotropic in the presence of an external magnetic field, we derive the dispersion equations; we show that the photonic spectrum of this superlattice loses its degeneracy and splits into two branches due to the external magnetic field. Interestingly, our results indicate that a superlattice that was previously wholly photo-isolating can become entirely photo-conducting, regardless of the direction of the external magnetic field applied. These results could be helpful to design and build new optical diode-like devices.

Asymmetric Magneto-Optical Rotation in Magnetoplasmonic Nanocomposites

The results of the asymmetric magneto-optical rotation in the magnetoplasmonic nanocomposite study are presented. The asymmetry is observed in spectra of magneto-optical rotation when a magneto-optical medium with a plasmonic subsystem is magnetized along or against the radiation wave vector. The asymmetry is observed as vertical displacement of a magneto-optical hysteresis loop too. Such asymmetry is detected in magnetoplasmonic nanocomposite, which consists of a magneto-optical layer of Bi substituted iron-garnet intercalated with a plasmonic subsystem of gold self-assembled nanoparticles. It is shown that the physical reason for the asymmetric magneto-optical rotation is the manifestation of the Cotton–Mouton birefringence effect when the normal magnetization of the sample to a radiation wave vector appears due to the magnetic component of the electromagnetic field of resonating nanoparticles. This effect is additive to the basic magneto-optical Faraday Effect.

All-magneto-optical grating bio-sensors based on enhanced transverse magneto-optical Kerr effect

Herein, a novel structure composed of an all-magneto-optical periodic grating, without using noble metals, is presented to enhance the transverse magneto-optical Kerr effect (TMOKE). This is done by calculating the relative changes in the reflection amplitudes for the p-polarized wave using the finite element method (FEM) with COMSOL Multiphysics. Bio-sensing applications of the proposed structure can be possible by detecting alternation in the refractive index of the analyte medium through monitoring of the TMOKE. The simultaneous operation of the magneto-optic layer as a sensing layer is the advantage of our idea, where direct interaction with the analyte happens, leading to the suppression of the wave reflection amplitudes, and finally leading to extreme TMOKE in a magneto-optical (MO) grating (the TMOKE amplitudes are near 0.8 in this work). And since TMOKE shows a Fano-like shape, we calculate sensitivity and figure of merit (FoM) by fitting them together. This results in high sensitivity, and the value of the FoM is remarkable (between 2×103 and 3×103 refractive index unit) at resonance angles for different refractive indices, which makes our proposed structure able to be utilized for bio-sensing applications.

Picosecond magneto-optic thermometry measurements of nanoscale thermal transport in AlN thin films

The thermal conductivity Λ of wide bandgap semiconductor thin films, such as AlN, affects the performance of high-frequency devices, power devices, and optoelectronics. However, accurate measurements of Λ in thin films with sub-micrometer thicknesses and Λ > 100 W m−1 K−1 is challenging. Widely used pump/probe metrologies, such as time–domain thermoreflectance (TDTR) and frequency–domain thermoreflectance, lack the spatiotemporal resolution necessary to accurately quantify thermal properties of sub-micrometer thin films with high Λ. In this work, we use a combination of magneto-optic thermometry and TiN interfacial layers to significantly enhance the spatiotemporal resolution of pump/probe thermal transport measurements. We use our approach to measure Λ of 100, 400, and 1000 nm AlN thin films. We coat AlN thin films with a ferromagnetic thin-film transducer with the geometry of (1 nm-Pt/0.4 nm-Co)x3/(2 nm-TiN). This PtCo/TiN transducer has a fast thermal response time of <50 ps, which allows us to differentiate between the thermal response of the transducer, AlN thin film, and substrate. For the 100, 400, and 1000 nm thick AlN films, we determine Λ to be 200 ± 80, 165 ± 35, and 300 ± 70 W m−1 K−1, respectively. We conclude with an uncertainty analysis that quantifies the errors associated with pump/probe measurements of thermal conductivity, as a function of transducer type, thin-film thermal conductivity, and thin-film thickness. Time resolved magneto-optic Kerr effect experiments can measure films that are three to five times thinner than is possible with standard pump/probe metrologies, such as TDTR. This advance in metrology will enable better characterization of nanoscale heat transfer in high thermal conductivity material systems like wide bandgap semiconductor heterostructures and devices.

Unidirectional propagation based on nonreciprocal defect modes in one-dimensional magneto-optical photonic crystals

In this study, in order to achieve the nonreciprocal propagation properties of electromagnetic waves, a ternary asymmetrical magneto-optical multilayer structure with a defect layer is constructed. It was found that, due to the defect layer, three pair nonreciprocal dispersive curves in three band gaps are formed for forward and backward incident waves. With the increasing thickness of defect layer, the nonreciprocal transmission peaks appear red-shift, and nonreciprocity decrease with enlargement of the space between two transmission peaks. Numerical simulations further indicated that the unidirectional propagation is due to the nonreciprocal resonant modes formed in the magneto-optical material layer of the ternary asymmetrical structure. These nonreciprocal properties are affected by the incident angle and the asymmetric gyrotropic electromagnetic parameters.

Insertion layer magnetism detection and analysis using transverse magneto-optical Kerr effect (T-MOKE) ellipsometry

This experimental study demonstrates that with transverse magneto-optical Kerr effect (T-MOKE) ellipsometry, it is possible to determine the magneto-optical and magnetic properties of insertion layers, even if they are superimposed onto much larger magnetic signals from the surrounding structure. Hereby, it turns out to be especially valuable that with T-MOKE ellipsometry one has full and precise quantitative access to the complex value of the magneto-optical reflection matrix component , because small magneto-optical insertion layer signals do not necessarily increase the absolute size of , but can lead to observable phase changes of this complex quantity instead. We demonstrate the ability of T-MOKE ellipsometry to precisely detect such small effects and hereby allow for an accurate determination of the alloy concentration dependent onset of ferromagnetism in ultrathin Co x Ru1−x insertion layers, that are embedded into a much thicker ferromagnetic structure. In addition, a detailed and quantitative signal analysis allowed us to demonstrate that the Co x Ru1−x insertion layers in our samples exhibit a magnetization reversal behavior that is independent of the adjacent Y3Fe5O12 layers, clearly indicating that both magnetic entities are either not or only very weakly coupled.

Near-field radiative heat transfer between one-dimensional magnetophotonic crystals

We present a theoretical study of the effect of an external dc magnetic field in the near-field radiative heat transfer between two one-dimensional magneto-photonic crystals with unit cells comprising a magneto-optical layer made of n-doped InSb and a dielectric layer. We find that in absence of an external field, and depending on the gap size, the radiative heat transfer between these multilayer structures can be larger or smaller than that of the case of two InSb infinite plates. On the other hand, when an external magnetic field is applied, the near-field radiative heat transfer is reduced as a consequence of the suppression of hybridized surface polariton waves that are supported for transverse magnetic polarized light. We show that such reduction is exclusively due to the appearance of magnetic-field induced hyperbolic modes, and not to the polarization conversion in this magneto-optical system.

Enhanced absorption study of one-way absorber based on magnetophotonic crystal combined with graphene

In this paper, a magnetophotonic crystal for enhanced absorption peak of one-way absorber is studied, in which two defect layers are introduced. The effects of magneto-optics and Tamm plasma polaritons are investigated. The optical properties of the novel photonic crystal with different periodic layer thicknesses and structures are shown in the wavelength range of 0.6–1.0 μm. Considering the large third-order nonlinearity and field localization, graphene is combined with the defect layer. Results showed that graphene can improve the absorption capacity of the absorber by 50%. Moreover, the influence of the relative position between graphene layer and magneto-optical layers on the absorption is further studied, which had found that this relative position can tune the absorption peak of the one-way absorber. Furthermore, the effect of incidence angle and the contour of electrical fields are also studied. Compared with the existing unidirectional devices, the structure has the advantages of small size, high efficiency, wide bandwidth and easy photoelectric integration. This work provides a new method for controllable perfect one-way absorber design in infrared wavelength range.

Nonreciprocal Fabry-Perot effect and performance enhancement in a magneto-optical InSb-based Faraday terahertz isolator.

The Faraday effect due to the cyclotron resonance of conduction electrons in semiconductor InSb allows for nonreciprocity of transmitted light in our Faraday THz isolator operating in the presence of a small magnetic field. We select InSb as an efficient medium for our isolator due to its high electron mobility, low electron effective mass, and narrow band gap. Experimental measurements of the isolator performance indicate a maximum achieved isolation power of 18.8 dB with an insertion loss of -12.6 dB. Our optical analysis of the device points to a remarkable nonreciprocal Fabry-Perot effect in the magneto-optical InSb layer as the origin of the multi-fold isolation enhancement. This nonreciprocity occurs as the Fabry-Perot reflections in the forward direction add constructively and enhance the transmittance at certain frequencies, while the Fabry-Perot reflections in the backward direction add destructively and suppress the transmittance at the same frequencies.

Determination of the parameters of coherent magneto-optical layers on a finite absorbing substrate from thermal radiation spectra

A possibility of determining the parameters of a coherent magneto-optical layer on a finite incoherent absorbing substrate by analyzing the spectra of its thermal radiation (TR) has been investigated. On the example of a plane-parallel InAs semiconductor plate silver-coated on the back surface, it has been shown that a complex analysis of TR spectra, both without and with the presence of magnetic field, makes it possible to determine the thickness, optical, magneto-optical and electric parameters of the layer. Algorithms for the calculation and analysis of TR spectra are adduced, which simplify determination of layer parameters and increase the accuracy of results. Comparing the position of the extremes of the experimental zero-field spectrum with the theoretical calculations, the thickness of the sample and the plasma oscillation frequency in the used semiconductor have been determined. The analysis of the relative contrast of interference oscillations in the TR spectrum in the magnetic field using previously defined parameters enabled to ascertain the spectral dependence of the Faraday rotation angle and to determine the concentration, effective mass and type of current carriers. It has been assumed, that such analysis of luminescence spectra also allows determining the parameters of magneto-optical layers and structures.

Hybrid of graphene surface plasmons and surface magneto-plasmons in a waveguide

The terahertz frequency has potential applications in various devices, and surface plasmons open up a number of promising applications. With the motivation of studying the possibility of hybridization of different surface plasmons, we proposed a waveguide structure with magneto-optical and dielectric layers with an air spacer layer in which a sheet of graphene is inserted between the dielectric and air gap. It is found that at terahertz frequencies, surface magneto-plasmons at the interface of air and magneto-optical material can interact with graphene surface plasmons which leads to the new type of hybrid plasmons. The coupling can be either tuned by external magnetic field, waveguide width, and the Fermi energy of graphene sheet. Our results show that at given values of waveguide parameters, huge enhancement of fields take place at a specific frequency. These findings open up new window to designing new plasmonic devices with desirable properties.

Comparison of the effects of surface plasmon resonance and the transverse magneto-optic Kerr effect in magneto-optic plasmonic nanostructures

In this letter, we report on the response of surface plasmon resonance (SPR, reflectance versus incident angle) and transverse magneto-optic Kerr effect (T-MOKE) versus incident angle) in two different magneto-optic-plasmonic (MOP) configurations: Ti/Au/Co/Au (Configuration A) and Ti/Ag/Co/Au (Configuration B) at the excitation wavelength of 780 nm in air. Configuration A includes a 35 nm Au layer and Configuration B includes a 35 nm Ag layer. Both configurations consist of a thin (4 or 8 nm) Co magneto-optic layer and showed an enhancement of the T-MOKE signal over the SPR signal. Configuration B showed higher SPR and T-MOKE responses over Configuration A, possibly due to the low loss and higher plasmonic properties of Ag over Au. The T-MOKE based sensor shows improvements in quality factor by over two times compared to that of SPR. The magneto-optic SPR sensitivity of the sensor obtained shows an improvement by three times over the SPR sensitivity, and this can be further improved by suitably modifying the configuration. These results are of importance to the development of enhanced MOP/plasmonic sensors.

Spin Hall effect of light in a prism-waveguide coupling structure with a magneto-optical bimetallic film

We study the spin hall effect of light (SHEL) in prism coupling configuration with magneto-optical (MO) material and bimetallic film which is called MOSHEL. Compared with single gold film, the surface plasmon resonance (SPR) with the bimetallic film can achieve minimum reflectivity and the difference between transverse shifts with opposite magnetic field directions can achieve 13 μm at resonance angle. By adjusting the thickness of magneto-optical layer and bimetallic film, we find that both SPR and SHEL can be modulated by the magnetic field. Base on this we propose that MOSHEL can be enhanced by MOSPR for the first time.

Full Experimental Determination of the Optical and Magneto-Optical Characteristics of a Hybrid Glass Waveguide Covered by a Magnetic Nanoparticles Doped Sol–Gel Layer

Optical waveguides, where propagating modes interact with a magnetized magneto-optical layer, show nonreciprocal properties, such as mode conversion, phase shift, and absorption. These properties are essential in order to make an efficient integrated isolator. In this paper, we explain how a well-calibrated polarimetric setup can be used to measure all the magneto-optical characteristics of a waveguide, in order to advance toward well-controlled integrated optical isolators.

Ultrasonic Spray Coating as a Fast Alternative Technique for the Deposition of Hybrid Magnetic‐Plasmonic Nanocomposites

Advanced applications in optics, for example, Faraday isolators, demand for complex magneto‐plasmonic nanostructures which exhibit large Faraday rotation. These structures is fabricated by a Layer‐by‐Layer approach, albeit this being a slow technique. Here, the ultrasonic spray coating as a promising alternative method toward the formation of hybrid magneto‐plasmonic structures is pioneered by the authors. Ultrasonic spray coating is a stable, fast, and tunable mass production method applied in this work to deposit gold and iron oxide nanoparticles. Altering multiple deposition parameters give the spray coating technique a large amount of control over the coverage. Optical and magneto‐optical properties, layer formation and surface coverage of single and hybrid layers with increasing thickness and number of layers are studied and compared to samples synthesized by Layer‐by‐Layer deposition. Ultrasonic spray coating paves the way to the widespread application of innovative and versatile hybrid magnetic‐plasmonic nanocomposites.

Magneto-Optical Device Based on Polarization Sensitivity for Perspective Biosensing Applications

Electromagnetic wave propagation in a structure comprising a magneto-optical layer placed on the top of a photonic crystal is theoretically studied. It is shown that the maximal rotation of the reflected wave polarization (Kerr–Faraday rotation) is achieved when wave vectors of TE and TM modes of the demagnetized structure are equal. The analysis of polarization ellipse—the Kerr–Faraday rotation angle—with respect to small changes of the dielectric permittivity of a medium adjoined to the magneto-optical layer demonstrated a high sensitivity of 25000°/RIU. We thus propose a novel design of perspective sensing elements for biosensing and chemical sensing.

Extremely high Faraday and Kerr rotations and extraordinary optical transmission in four-layer dielectric-metal strips-dielectric-Bi:YIG planar structure

Abstract Faraday and Kerr effects as well as the extraordinary optical transmission in a structure that combines magneto-optical and plasmonic properties are studied. The planar structure consists of four layers, namely, dielectric layer, metal strips, once again dieletric layer and magneto-optic one. The magneto-optical layer is magnetized by a DC magnetic field normal to it. Our numerical analysis shows that the Faraday and Kerr rotations in this structure can be increased by more than two times in comparison with the published results. This is achieved due to high Q-factor resonances in magneto-optic layer.

Properties of magnetic photonic crystals in the visible spectral region and their performance limitations

We report on the results of computer modelling and performance analysis of the optical and magneto-optical (MO) characteristics of one-dimensional magnetic photonic crystals (MPC) of several classic design types (having either a single structure defect, or a number of these), designed for applications in the visible spectral region. The calculations are performed accounting for the real levels of optical absorption achievable in existing MO materials which currently demonstrate the best MO quality (bismuth-substituted ferrite garnets). We consider Bi2Dy1Fe4Ga1O12 as the base material for use within quarter-wave thick MO layers of MPC; silica is used for the non-magnetic transparent quarter-wave layers. The achieved results can be used to clarify the nature of the differences that exist between the expected practical potential of MPCs in integrated photonics, and the actual attained experimental results. Our results show that in MPCs optimized for light intensity modulation applications, in the red spectral region (near 650nm), the achievable levels of optical transmission are limited to about 30%. This coincides spectrally with the peaks of Faraday rotation reaching their maxima at about 25°, with further transmission increases possible in the near-infrared region. Larger Faraday rotation angles are only achievable currently in structures or single film layers with reduced transmission.

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.

Highly tunable bistability using an external magnetic field in photonic crystals containing graphene and magnetooptical layers

In this paper, we propose an optical bistable structure based on a single graphene layer sandwiched between two magnetooptical layers which are located between two photonic crystals. It is indicated that such structure shows optical bistability behaviors, in the near infrared range, which can be efficiently controlled with small external magnetic fields lower than 1.5 mT. Such weak external magnetic fields cannot affect the graphene layer and the dependence of bistability phenomenon on the magnetic field results from the presence of magnetooptical layers and their influences on the resonance frequency of the structure. Both switch-up and switch-down thresholds can be significantly adjusted by variation of the external magnetic field. Furthermore, the width of hysteresis loop enhances with increasing the magnetic field. To obtain a high tunability of bistability with external magnetic fields, the thickness of magnetooptical layers should be larger than a special value. It is also found that the increase of the Fermi energy level of graphene leads to the enhancement of both switch-up and switch-down thresholds as well as the width of the hysteresis loop. Finally, it is confirmed that optical bistability can be manipulated by changing the incident illumination angle.