Recently, the terahertz family of sources increased by newly-developed terahertz spintronic emitter (STE), which competes with the traditional in many ways. This 30THz-broadband gapless source is versatile due to its low-cost, easy implementation, frequency-independent excitation, and perpendicularly-given polarization to the STE’s magnetization. Nowadays, the polarization control of STEs was demonstrated by rotating and multipolar magnets, a twisted magnetic field, or cascades of STEs. The methods suffer from mechanical stability, realization difficulties, and limited polarization control. We introduce here our new approach to control the emitted polarization following Stoner-Wohlfarth magnetization rotation within our FeCo/TbCo2/FeCo-based STE exploiting magnetic anisotropy. The varying magnetic field along the hard magnetic axis induces the magnetization rotation, performing the polarization control. We present full-360-degree linear polarization control, not needing mechanically rotating components. This technique guarantees higher stability for polarimetry applications. We prove the whole terahertz spectrum follows the polarization control, preserving even the phase of sub-picosecond terahertz emission. It offers easy polarization calibration of the emitter for terahertz experimental setups. Moreover, we provide models to explain magnetic hysteresis defining the polarization behaviour. We predict that the polarization-controlled STEs will find many applications covering terahertz time-domain polarimetry and ellipsometry, medical imaging and security detection.
We present a scheme to achieve coherent polarization rotation without multipolar or rotating external magnetic bias nor complex cascaded emitters, by exploiting artificially engineered strong uniaxial anisotropy in intermetallic heterostructures of rare-earth and transition metals. By replacing the FM layer of the spintronic emitter with a carefully designed FeCo/TbCo2/FeCo heterostructure, we demonstrated Stoner-Wolfarth-like coherent rotation of the THz polarization only by a unipolar variation of the strength of the hard axis field. In a second step we demonstrated the magnetoelectric control of the polarization direction. These results improve greatly the feasibility of fast polarization switchable integrated THz sources impacting practical applications such as ultrabroadband THz spectroscopic ellipsometry without rotating elements, or polarization modulated high speed wireless data communications, but also fundamental physical studies into ultrafast terahertz optospintronics.
In this proceeding, we present a software Fit@TDS that enables to retrieve the refractive index of a sample from a timedomain spectroscopy experiment. The software include commonly used methods where the refractive index is extracted from frequency domain data. This method has limitations when the signal is too noisy or when the absorption peak saturates the absorption. Thus, the software includes as well a new method where the refractive index are directly fitted using a model (the Drude-Lorentz for example) in the time domain. This method uses an optimization algorithm that retrieves the parameters of the model corresponding to the studied material. In this proceeding, we explain the methods and test them on fictitious samples to probe the feasibility and reliability of the proposed model.
In this paper we apply the terahertz time-domain spectroscopy (THz-TDS) to obtain optical function spectra in the range from 0.06 to 3 THz. Polarization sensitivity is obtained using azimuth-controlled wire-grid polarizers. We demonstrate general methods on characterization of plasmonic semiconductors. Detail characterization of optical and magneto-optical material properties is also motivated by a need of optical isolator in THz spectral range. The technique is applied to III-V semiconductors. The typical material is a single crystal undoped InSb having the plasma frequency in the range of interest. With appropriate magnetic field (in our case 0.4 T) we observed coupling of plasma and cyclotron behavior of free electrons with gigantic magneto-optic effect in the THz spectral range.
In this paper we present our study of waveguiding structure with nonreciprocal dispersion of guided modes. The
considered structure is based on the Silicon waveguide core and the plasmonic (gold) 1D periodic grating. The
waveguide and the grating are separated by low refractive index layer (SiO2). The structure operates as follows.
The evanescent field of the guided mode is used for the excitation of the surface plasmon polaritons (SPPs) at the
top side of the grating. To achieve non-reciprocity the magneto-optical dielectric garnet is assumed to be on the
top of the grating. The presence of the transversal magnetization in the garnet leads to the nonreciprocal shift
of the SPP. Together with the evanescent coupling of guided modes this leads to the nonreciprocal dispersion
of guided mode. The grating period is varied to achieve coupling of grating’s resonances with the waveguide
evanescent field and therefore possible enhancement of the nonreciprocal response.
Interest in nonreciprocal terahertz (THz) integrated optics makes necessity to look for new materials active in this region and precisely characterize their optical properties. In this paper we present important aspects of the methods for determination of optical functions in far infrared (FIR) and THz spectral range. The techniques are applied to polyethylene cyclic olefin copolymer (Topas) and hexaferrites (BaFe12O19, SrFe12O19). Topas is promising material in integrated optics for THz radiation, thanks to its low absorption in this region. On the other hand, hexaferrites with its magneto-optic properties can be used for nonreciprocal integrated optic parts and radiation control. Samples were studied by THz time domain spectroscopy (THz-TDS) in spectral range 2 - 100 cm-1 by transmission and reflection. Advantage of presented THz time domain spectroscopy is measurement of the electric field wavefunction, which allows to obtain both the amplitude and phase spectra. In results we provide measured data, processing, and final computed optical properties of Topas and hexaferrites which reveal interesting optical behaviour in THz spectral range.
In this paper, we review two main recently dominating applications of magneto-optics (MO). The first one is related to a unique MO non-reciprocity. For example, the MO non-reciprocity in the isolators enables complete transmission in the forward propagation direction, while it prevents spurious back-reflection, which is needed to preserve proper operation of active optical elements like lasers or amplifiers in optical systems. Local enhancement of MO activity by optical field concentration in nanostructured magneto-plasmonic and magneto-photonic systems opens new horizons in optical isolators, circulators, and switches. We will discuss enhancement of MO effects using surface magneto-plasmons in periodic grating and apply it to nonreciprocal isolating systems. The second main application of the magneto-optics is the characterization of magnetic multilayers, periodic systems, and nanostructures. MO techniques profit from high near-surface sensitivity to local magnetization, nondestructive character, ultrafast response, and possibility to measure all components of the magnetization vector by means of MO vector magnetometry. Furthermore, the MO Kerr effect allows the separation of magnetic contributions originating in different depths, different materials in multilayer systems as well as laterally modulated and self-organized nanostructures fabricated via modern nanotechnologies.
In this paper we analyze the optical and transversal magnetooptical (MO) response of magnetoplasmonic (MP) nanostructures. The MP structure is a 1D periodic gold grating fabricated by lift-off technique on the MO dielectric substrate (Bi-substituted yttrium iron garnet BixY3−xFe5O12). Following our recent theoretical work (Opt. Express 21, pp. 2174121755, Sep 2013.), we confirm here experimentally the predicted dependence of the MO response on the geometry of the grating, that is directly attributed to the anticrossing behavior of the Fabry-Perot (FP) resonance in the grating’s slits and the surface plasmon resonances (SPPs) at its interfaces. The experimental results were achieved by Mueller matrix spectroscopic ellipsometry. Observed fine tuning of the transverse magneto-optic Kerr opens up new possibilities for the design of compact nonreciprocal devices.
We have demonstrated numerically that the interface of a metal and uniformly magnetized two-dimensional photonic
crystal fabricated from a transparent dielectric magneto-optic (MO) material possesses a one-way frequency range where
only a forward propagating surface plasmon polariton (SPP) mode is allowed to propagate. The nonreciprocity at the
interface is introduced by the MO properties of the photonic crystal that is fabricated from Bismuth Iron Garnet (BIG,
Bi3Fe5O12), a ferrimagnetic oxide which may be easily magnetically saturated by fields of the order of tens of mT.
Therefore, this configuration allows to achieve sizable one-way bandwidth by using significantly smaller values of the
external magnetic field than an analogous waveguide proposed by Yu1 which makes such a waveguide favorable for
design of diode-like elements in optical integrated circuits. By using simple analytical model we have determined one-way
frequency range which is consistent with the results obtained previously by using a MO aperiodic Fourier Modal
Method (MO a-FMM). To investigate transport properties of the structures within this frequency range we have
implemented finite-difference time-domain(FDTD) method, that allows calculating the propagation of EM waves
through media with full tensorial magneto-optic permittivity. We examined the unidirectional transport properties of the
proposed one-way waveguide and studied how the nonreciprocity depends on boundary conditions, for instance, by
placing a perfect conducting mirror at the end of one-way waveguide.
We have demonstrated numerically that a waveguide formed by the interface of a metal and uniformly magnetized twodimensional
photonic crystal fabricated from a transparent dielectric magneto-optic (MO) material possesses a one-way
frequency range where only a forward propagating surface plasmon polariton (SPP) mode is allowed to propagate. In
contrast to an analogous waveguide proposed by Yu1 the non-reciprocity at the interface is introduced by the MO
properties of the photonic crystal material and not by applying an unrealistically high static magnetic field (up to 1 T) on
metal described by free-electron Drude form of the dielectric function. The considered magnetic material is Bismuth Iron
Garnet (BIG, Bi3Fe5O12), a ferrimagnetic oxide which may be easily magnetically saturated by fields of the order of tens
of mT. Therefore, this configuration allows to achieve sizable one-way bandwidth by using significantly smaller values
of the external magnetic field which makes such a waveguide favorable for design of diode-like elements in optical
integrated circuits. By using a novel MO aperiodic Fourier Modal Method (MO a-FMM) to calculate the band structure
of this magneto-plasmonic photonic crystal waveguide we have proven the existence of one-way SPP bands within the
optical wavelength.To investigate transport properties of the structures within this frequency range we have implemented
two finite-difference time-domain (FDTD) methods, namely ADE2 and that based on Z-transforms3 that allow
calculating the propagation of EM waves through media with full tensorial magneto-optic permittivity. We provide
numerical evidence confirming suppression of disorder-induced backscattering in the one-way waveguide.
Using rigorous magneto-optical waveguide modelling, we have calculated the dichroic transmission of the fundamental
TM waveguide mode through a magnetoplasmonic waveguide grating. The ferromagnetic metallic grating material is a
CoFe alloy that is magnetized parallel to the grating. When deposited on top of a standard III-V waveguide with a thin
top cladding layer and thus placed in the evanescent tail of the guided TM ground mode, it induces both plasmonic and
magneto-optic effects in the transmission of this waveguide grating. Due to the direction of the magnetization -
perpendicular to the light propagation and parallel to the waveguide layer interfaces - the integrated transverse magnetooptic
Kerr effect induces non-reciprocal dichroic transmission for the guided TM light. We have numerically studied the
TM ground mode dichroism (for a telecom wavelength of 1300nm) as a function of the cladding layer thickness and the
grating parameters, namely its duty cycle, period and thickness. This study has revealed that there exist clear grating
designs where the dichroic transmission is resonantly enhanced as compared to the case where the ferromagnetic metal is
a continuous film. A detailed study of the field maps associated to these points reveals that the guided TM ground mode
resonantly couples to a vertical cavity plasmonic resonance in the air slots of the CoFe grating. This behaviour is
reminiscent of extraordinary optical transmission but here in an integrated non-reciprocal version. We have previously
reported experimentally strong integrated and forward transparent optical isolation based on this TM dichroism but using
a continuous film [1,2]. The present design study indicates that the extraordinary magnetoplasmonic effects taking place
in a properly designed CoFe grating improves the performance of this device by at least a factor 4.
Magneto photonic crystals exhibit unique combination of
magneto-optical nonreciprocity and resonant behavior
originating from periodic structure. Modeling of magneto photonic structures requires inclusion of magnetic induced
anisotropy and description of medium using a permittivity tensor. On the other hand, differential theory of periodic
gratings based on Fourier expansion of permittivity tensor and electromagnetic field is recently frequently applied. In
this paper we propose an approach of effective propagation constant calculation from scattering matrix of the waveguide
consisting of the anisotropic magneto-optical lamellar grating. The structure is modeled using Rigorous Coupled Wave
Analysis (RCWA) extended by Fourier factorization method. The approach is applied to optimize parameters of
integrated magneto-optic waveguide isolator with lamellar grating from magneto-optic medium at transverse geometry.
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