We demonstrate spectral and scattering properties of a photonic implementation of a modified Fano-Anderson model. The model includes formation of a symmetry-protected bound state in the continuum (BIC). We interpret the scattering spectra of the structures with the broken symmetry in terms of system eigenmodes. The Fano resonance associated with the excitation of quasi-BIC is explained as arising from the interference between this mode and another leaky mode.
We investigate the scattering properties of the finite periodic structure consisting of the PT dipoles represented by gain/loss cylinders arranged in a 2D honeycomb lattice. We found that the total scattered energy reveals series of sharp resonances at which the energy increases by two orders of magnitude and an incident wave with arbitrary frequency is scattered only in a few directions given by spatial symmetry of periodic structure. Both features can be qualitatively explained by analysis of the complex band structure associated with an infinite honeycomb array of the PT dipoles which supports
the broken PT-symmetric phase at the symmetry points and along the ΓK and ΓM directions and provides the mechanisms leading to a significant enhancement of the radiated power and offers a plausible explanation to highly-directional scattering pattern. Specifically, we assigned the lowest resonance in the total scattering energy to the broken PT-symmetry mode formed by a doubly degenerate pair with complex conjugate eigenfrequencies corresponding to the K-point of the reciprocal lattice.
Based on magnetooptic Fourier modal method (MOaRCWA) simulations, both in 2D in 3D, we have studied the magnetoplasmons in plasmonic nanostructures, such as InSb within the THz spectral region. One of only few possibilities how to impose nonreciprocity in guiding subwavelength structures is to apply an external magnetic field (mainly in the Voigt configuration). In such a case, one-way (nonreciprocal) propagation of SP is not only possible but may bring many interesting phenomena in connection with magnetoplasmons (MSP). We have developed an efficient 2D and 3D numerical technique based on MO aperiodic rigorous coupled wave analysis – MOaRCWA. In our in-house tool, the artificial periodicity is imposed within a periodic 1D and 2D RCWA methods, in the form of the complex transformation and / or uniaxial perfectly matched layers. We have combined the MOaRCWA simulations with (quasi)analytical predictions in order to study MSP performance of plasmonic nanostructures with highly-dispersive polaritonic InSb material, in the presence of external magnetic field. Here, Voigt MO effect can be used to impose nonreciprocity (one-way propagation) bringing new interesting phenomena in connection with MSP. We have successfully applied our 2D and 3D numerical MOaRCWA technique to several interesting structures, such as THz a novel type of one-way structure, designed as a combination of the InSb and 3D hybrid dielectric-plasmonic slot waveguide, and others.
Based on magnetooptic Fourier modal method (MOaRCWA) simulations, both in 2D in 3D, we have studied the magnetoplasmons in plasmonic nanostructures, such as InSb within the THz spectral region. One of only few possibilities how to impose nonreciprocity in guiding subwavelength structures is to apply an external magnetic field (mainly in the Voigt configuration). In such a case, one-way (nonreciprocal) propagation of SP is not only possible but may bring many interesting phenomena in connection with magnetoplasmons (MSP). We have developed an efficient 2D and 3D numerical technique based on MO aperiodic rigorous coupled wave analysis – MOaRCWA. In our in-house tool, the artificial periodicity is imposed within a periodic 1D and 2D RCWA methods, in the form of the complex transformation and / or uniaxial perfectly matched layers. We have combined the MOaRCWA simulations with (quasi)analytical predictions in order to study MSP performance of various plasmonic nanostructures, such as basen on a highly-dispersive polaritonic InSb material, in the presence of external magnetic field. Here, Voigt MO effect can be used to impose nonreciprocity (one-way propagation) bringing new interesting phenomena in connection with MSP. We have successfully applied our 2D and 3D numerical MOaRCWA technique to several interesting structures, such as THz filters with magnetooptical Bragg grating, a combined 3D InSb - hybrid dielectric-plasmonic slot waveguide structure, etc. The obtained results will be discussed and the perspective will be given.
One of only few possibilities how to impose nonreciprocity in guiding subwavelength structures is to apply an external magnetic field (mainly in the Voigt configuration). In such a case, one-way (nonreciprocal) propagation of SP is not only possible but may bring many interesting phenomena in connection with magnetoplasmons (MSP). We have developed an efficient 2D numerical technique based on MO aperiodic rigorous coupled wave analysis – MOaRCWA. In our in-house tool, the artificial periodicity is imposed within a periodic 1D RCWA method, in the form of the complex transformation and / or uniaxial perfectly matched layers. We have combined the MOaRCWA simulations with (quasi)analytical predictions in order to study MSP performance of plasmonic nanostructures with highly-dispersive polaritonic InSb material, in the presence of external magnetic field. Here, Voigt MO effect can be used to impose nonreciprocity (one-way propagation) bringing new interesting phenomena in connection with MSP. As an example of interesting structures studied, InSb-based THz waveguides were analyzed. We have shown that the one-way bandwidth can be controlled by an external magnetic field and by the permittivity and thickness of the dielectric guiding layer. Based on such analysis of simple guiding structures, we have proceeded with modeling of several more complex magnetooptical InSb microstructures in THz range. Finally, recently, we have worked on the extension of our MOaRCWA numerical tool to fully 3D case.
We describe a surface structure that possesses a different transmissivity for a surface plasmon polariton incident on it from one side of it than it has for a surface plasmon polariton incident on it from the opposite side. This asymmetric transmission of a surface plasmon polariton does not require either electrical nonlinearity or the presence of a magnetic field but is a consequence solely of the geometry of the structure. We have demonstrated that a system consisting of a square array of scatterers deposited on a metal surface in a triangular mesh to which a diffractive structure is added to the left side of it reveals asymmetric transmission when the frequency of the incident SPP is in the bandgap of the plasmonic crystal. The mechanism for this property is related to the higher Bragg modes that are excited due to the diffractive structure, while the 0-order beam, due to the existence of the band gap, is not transmitted through the structure. By varying the material and geometrical parameters of the diffractive structure one can control the contrast transmission that characterizes the degree of the asymmetry.
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.
Passive real-world waveguiding structures are inevitably lossy, and some of them, such as plasmonic waveguides,
exhibit even very strong attenuation. Losses can be compensated by including active components with gain. In this paper
we discuss properties of waveguiding structures with generally complex dielectric permittivity distributed across their
cross-section. In particular, we focus on the existence of modes that exhibit balance between loss and gain and that can
propagate unattenuated provided the suitable conditions are satisfied. Specifically, we examine power transmission in the
structures with a balance of loss and gain supporting lossless propagation of two modes. We demonstrate that when both
modes are excited simultaneously, the total transmitted power is not conserved as the modes propagate along the
waveguide. We also show that even if one of the modes propagates with gain, the maximum attainable transmitted power
is strongly influenced by back-reflections from the interface with the passive output waveguide. We also discuss the
conditions for the existence of an un-attenuated propagation of a confined surface mode supported by the gain/loss
nature of these photonic structures.
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.
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