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In the present work, we demonstrate scattering properties of parity-time (PT) symmetric one-dimensional bilayer structure with spatially distributed gain and loss in the dielectric layers. We report the effect of parabolic modulation of loss and gain on the non-Hermitian characteristics of the PT-symmetric system such as exceptional points (EPs), lasing points (LPs), and coherent perfect absorption (CPA) for normal and oblique illuminations for TE & TM polarizations. We observe a significant enhancement in CPA-LP, which also shows a red shift with parabolic modulation in the spatially distributed imaginary part of the dielectric permittivity for the normal incident waves. On the other hand, under oblique incidence, the spatial parabolic modulation in gain–loss tunes all the scattering properties of PT-symmetric systems such as CPA-LP and EPs. In addition, we have also investigated the effect of the introduction of a silicon layer with varying thickness between the bilayer exhibiting gain and loss on EPs and CPAs. The optical properties of the PT-symmetric structure under consideration are studied by employing the scattering and transfer matrix method and all these results are further corroborated with COMSOL® Multiphysics simulations. The proposed PT-symmetric system exhibits promising applications to achieve CPA, exotic lasing, phase modulators, and optical isolators due to the non-reciprocal behaviour of the bilayer system. [ABSTRACT FROM AUTHOR]

Reciprocal scatterers necessarily extinguish the same amount of incoming power when excited from opposite directions. This property implies that it is not possible to realize scatterers that are transparent when excited from one direction but that scatter and absorb light for the opposite excitation, limiting opportunities in the context of asymmetric imaging and nanophotonic circuits. This reciprocity constraint may be overcome with an external bias that breaks time-reversal symmetry, posing however challenges in terms of practical implementations and integration. Here, we explore the use of tailored nonlinearities combined with geometric asymmetries in suitably tailored resonant nanoantennas. We demonstrate that, under suitable design conditions, a nonlinear scatterer can be cloaked for one excitation direction, yet strongly scatters when excited at the same frequency and intensity from the opposite direction. This nonreciprocal scattering phenomenon opens opportunities for nonlinear nanophotonics, asymmetric imaging and visibility, all-optical signal processing and directional sensing.

Nonreciprocal transmission, reflection and absorption are very important in quantum science. For their realization, cavity magnonics is attracting much attention, where Kittel mode describing collective excitations of a large number of spins is excited through driving magnons with a strong microwave field. The cavity photons and magnons are coupled via magnetic dipole interaction, while the magnons and phonons are coupled via magnetostrictive interaction. By applying experimental feasible parameters, we breaks the symmetry of spatial inversion in order to realize nonreciprocal transmission, reflection absorption. Our results reveal a new strategy to protect quantum resources for building noise-tolerant quantum processors, realizing chiral networks, and invisible quantum sensing.

Abstract Nonreciprocal interlayer coupling is difficult to practically implement in bilayer non-Hermitian topological photonic systems. In this work, we identify a similarity transformation between the Hamiltonians of systems with nonreciprocal interlayer coupling and on-site gain/loss. The similarity transformation is widely applicable, and we show its application in one- and two-dimensional bilayer topological systems as examples. The bilayer non-Hermitian system with nonreciprocal interlayer coupling, whose topological number can be defined using the gauge-smoothed Wilson loop, is topologically equivalent to the bilayer system with on-site gain/loss. We also show that the topological number of bilayer non-Hermitian C6v-typed domain-induced topological interface states can be defined in the same way as in the case of the bilayer non-Hermitian Su–Schrieffer–Heeger model. Our results show the relations between two microscopic provenances of the non-Hermiticity and provide a universal and convenient scheme for constructing and studying nonreciprocal interlayer coupling in bilayer non-Hermitian topological systems. This scheme is useful for observation of non-Hermitian skin effect in three-dimensional systems. Graphical Abstract

Nonreciprocal interlayer coupling is difficult to practically implement in bilayer non-Hermitian topological photonic systems. In this work, we identify a similarity transformation between the Hamiltonians of systems with nonreciprocal interlayer coupling and on-site gain/loss. The similarity transformation is widely applicable, and we show its application in one- and two-dimensional bilayer topological systems as examples. The bilayer non-Hermitian system with nonreciprocal interlayer coupling, whose topological number can be defined using the gauge-smoothed Wilson loop, is topologically equivalent to the bilayer system with on-site gain/loss. We also show that the topological number of bilayer non-Hermitian C6v-typed domain-induced topological interface states can be defined in the same way as in the case of the bilayer non-Hermitian Su–Schrieffer–Heeger model. Our results show the relations between two microscopic provenances of the non-Hermiticity and provide a universal and convenient scheme for constructing and studying nonreciprocal interlayer coupling in bilayer non-Hermitian topological systems. This scheme is useful for observation of non-Hermitian skin effect in three-dimensional systems. [ABSTRACT FROM AUTHOR]

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A multicomponent mixture of Janus colloids with distinct catalytic coats and phoretic mobilities is a promising theoretical system to explore the collective behavior arising from nonreciprocal interactions. An active colloid produces (or consumes) chemicals, self-propels, drifts along chemical gradients, and rotates its intrinsic polarity to align with a gradient. As a result the connection from microscopics to continuum theories through coarse-graining couples densities and polarization fields in unique ways. Focusing on a binary mixture, we show that these couplings render the unpatterned reference state unstable to small perturbations through a variety of instabilities including oscillatory ones which arise on crossing an exceptional point or through a Hopf bifurcation. For fast relaxation of the polar fields, they can be eliminated in favor of the density fields to obtain a microscopic realization of the Nonreciprocal Cahn–Hilliard model for two conserved species with two distinct sources of non-reciprocity, one in the interaction coefficient and the other in the interfacial tension. Our work establishes Janus colloids as a versatile model for a bottom-up approach to both scalar and polar active mixtures.

Chiral quantum optics is a new research area in light-matter interaction that depends on the direction of light propagation and offers a new path for the quantum regulation of light-matter interactions. In this paper, we study a spinning Kerr-type microresonator coupled with Λ-type atom ensembles, which are driven in opposite directions to generate asymmetric photon statistics. We find that a photon blockade can only be generated by driving the spinning resonator on right side without driving the spinning microresonator from the left side, resulting in chirality. The coupling strength between system modes can be precisely controlled by adjusting the detuning amount of the atomic pump field. Because of the splitting of the resonant frequency generated by the Fizeau drag, the destructive quantum interference generated in right side drive prevents the nonresonant transition path of state ∣1,0〉 to state ∣2,0〉. This direction-dependent chiral quantum optics is expected to be applied to chiral optical devices, single-photon sources and nonreciprocal quantum communications. [ABSTRACT FROM AUTHOR]

Kirchhoff's law shows that reciprocal materials have equal spectral emissivity at two symmetric polar angles, which is a fundamental limit for a thermal emitter to achieve a small angular divergence in the normal direction. Nonreciprocal materials allow violation of Kirchhoff's law as the emissivity at the two symmetric polar angles can be different. However, achieving strong nonreciprocal thermal radiation near zero angle is challenging. In this work, to reduce the power consumption of a light source for e.g. gas sensing, an ultra‐high‐directional nonreciprocal thermal vertical emitter is proposed, with a periodic structure of magneto‐optical material. When B = 3 T or 1.5 T, magneto‐optical lattice resonances enable the near‐perfect emissivity at 22.36 µm or 22.99 µm at zero angle. The strong nonreciprocity contributed by the collective modes allows for a near‐complete violation of Kirchhoff's law at small angles of ±1°. The nonreciprocal emitters have a very small angular divergence (≈1°), which is better than that of the state‐of‐the‐art thermal emitters. The highly directional nonreciprocal thermal emission is robust despite ±25% change in material loss and ±5% fluctuation in structural parameters. This work should inspire the design of high‐directional nonreciprocal thermal emitters and their applications in high‐resolution thermal imaging, infrared gas sensing, biomedical breath monitoring, and so on. [ABSTRACT FROM AUTHOR]

In micro/nano-scaled structures, film has more practical application value for its smooth surface, easy to prepare, more universal, and stable. InSb is a semiconductor material widely used in infrared detection and imaging. In this paper, we demonstrate that the magneto-optical InSb film embedded with Au hemispherical particles in the infrared wavelength of 4–5 μm can behave as a nonreciprocal absorber. Lorentz-Drude model is used to describe the permittivity of InSb in this work. Theoretical analysis shows that the average absorption is greater than 0.5. The physical origin of high nonreciprocal absorption is related to the local surface plasmon resonance (LSPR) of the hemispherical particles. Additionally, the effects of particle radius, incident angle, and direction on nonreciprocal absorption performance are analyzed in detail. The electric field diagram intuitively shows the enhancement mechanism of LSPR to the magneto-optical effect. We believe that our design has a promising application in infrared absorbers, infrared detection, and imaging equipment. [ABSTRACT FROM AUTHOR]

This work explores micromachined heterostructured waveguides that leverage strong interactions between acoustic phonons and electrons to enable radio frequency (RF) signal amplification or attenuation. A thin-film piezoelectric-on-semiconductor stack is tailored to generate high electromechanical coupling Lamb waves that are impacted by high mobility electrons within a microacoustic waveguide. Lamb waves are generated by RF signal via interdigital electrodes on the piezoelectric layer; by applying a voltage to the semiconductor layer so that the electrons lead mechanical waves, the RF signal is amplified through the acoustoelectric (AE) effect. Conversely, the signals propagating faster or in the opposite direction of the electron flow undergo attenuation, rendering the waveguide nonreciprocal. Research on the AE effect dates to the mid-20th century and until now has been mostly focused on surface acoustic waves (SAWs). In this work, enabled by high-quality bonded thin films of lithium niobate (LN) and silicon (Si), it is shown that fundamental symmetric ($S0$) Lamb mode waveguides at 100 s of MHz can achieve more than 40 dB of AE gain and strong nonreciprocal transmission with less than 10 mW of bias power consumption. This could enable implementation of switches, delay lines, isolators, and circulators, which are critical for interference cancellation and full-duplex radio. The AE effect is observed to be stronger in some higher $S0$ harmonics, allowing for scaling to higher frequencies with optimized electrodes that have more relaxed critical dimensions. In addition, up to 5.5-dB sustained terminal gain measured in this work implies the potential for transistor-less amplifiers that could be implemented in concert with more traditional acoustic devices in a single-chip manner. [ABSTRACT FROM AUTHOR]

An adjustable unidirectional amplifier is proposed in a hybrid cavity magnonic system. By eliminating the rapidly dissipative auxiliary mode, we obtain the effective Hamiltonian for a typical three-body circulator. Through analyzing the transmission coefficients of the system, we find that the nonreciprocal transmission of photon–magnon as well as the amplification of arbitrary signals can be both realized without requiring in the parity-time symmetry condition. In addition, the amplification factor of our system is highly adjustable. Our theoretical scheme has potential implication in realizing magnonic triodes and magnon-based quantum information processing. • Adjustable nonreciprocal amplification between magneto-optical and photo-optical effects is achieved. • Unlike the amplification mechanisms in active devices (such as PT gain), we achieve amplification by constructing local gain within an overall passive device, introducing a novel concept of nonreciprocal amplification. • We provide an analytical solution for the amplification coefficient and explore the dependence of the amplification effect on various physical quantities. [ABSTRACT FROM AUTHOR]

Nonreciprocal transmission, reflection and absorption are very important in quantum science. For their realization, cavity magnonics is attracting much attention, where Kittel mode describing collective excitations of a large number of spins is excited through driving magnons with a strong microwave field. The cavity photons and magnons are coupled via magnetic dipole interaction, while the magnons and phonons are coupled via magnetostrictive interaction. By applying experimental feasible parameters, we breaks the symmetry of spatial inversion in order to realize nonreciprocal transmission, reflection absorption. Our results reveal a new strategy to protect quantum resources for building noise-tolerant quantum processors, realizing chiral networks, and invisible quantum sensing. • Nonreciprocal transmission, reflection and absorption are very important in quantum science. • In our schemes, cavity photons and magnons are coupled via magnetic dipole interaction, while the magnons and phonons are coupled via magnetostrictive interaction. By applying experimental feasible parameters, we breaks the symmetry of spatial inversion in order to realize nonreciprocal transmission, reflection absorption. • Our results reveal a new strategy to protect quantum resources for building noise-tolerant quantum processors, realizing chiral networks, and invisible quantum sensing. [ABSTRACT FROM AUTHOR]

Nonreciprocal responses in noncentrosymmetric systems contain a broad range of phenomena. Especially, non-dissipative and coherent nonreciprocal transport in solids is an important fundamental issue. The recent discovery of superconductor (SC) diodes under external magnetic fields, where the magnitude of the critical current changes as the direction is reversed, significantly boosted this research area. However, a theoretical understanding of such phenomena is lacking. Here, we provide theoretical descriptions of SC diodes with a generalized Ginzburgâ€"Landau method. The theory is applied to Rashba spinâ€"orbit coupled systems, where analytical relations between the nonreciprocal critical currents and the system parameters are achieved. Numerical calculations with mean-field theory are also obtained to study broader parameter regions. These results offer a rather general description and design principles of SC diodes. [ABSTRACT FROM AUTHOR]

Nonreciprocal photonic devices are essential components of classical optical information processing. It is interesting and important to investigate their feasibility in the quantum world. In this work, a single‐photon non‐reciprocal dynamical transmission experiment has been performed with an on‐chip silicon nitride (SiN)‐based magneto‐optical (MO) isolator. The measured isolation ratio for single photons achieved is 12.33 dB, consistent with the result of the classical test, which proves the functionality of our on‐chip isolator. The quantum coherence of the passing single photons is further verified using high‐visibility quantum interference. This work will promote on‐chip nonreciprocal photonic devices within the integrated quantum circuits and help introduce novel phenomena in quantum information processes. [ABSTRACT FROM AUTHOR]

This letter presents a magnet-less nonreciprocal bandpass filter (BPF) that uses coupled static and time-modulated resonators. This coupling allows the nonreciprocal BPF to achieve minimum forward insertion loss (IL) and two pole isolation within the passband and shows wideband and high isolation. The modulation signal is directly applied to the varactor through the transmission line. This design, while simple, nevertheless achieves an excellent nonreciprocal response. We designed, simulated, and experimentally validated a microstrip line nonreciprocal BPF at 1.46 GHz. The results achieved in experiment were consistent with those obtained through simulations; forward IL of 3.10 dB and reverse isolation of 20 dB over a bandwidth of 50 MHz. [ABSTRACT FROM AUTHOR]

In this work, we propose, develop, and demonstrate a fundamental and comprehensive theoretical foundation for the first time to formulate and devise known and unknown reciprocal and/or nonreciprocal ferrite components with arbitrarily concurrent multimode features based on the substrate-integrated waveguide (SIW) technology. To achieve such a universal design, a nonreciprocal unit cell (NRUC) is first defined and characterized. Then, an approach is proposed and investigated to deploy a sufficient number of NRUCs next to each other as a kernel multimode SIW topology. The kernel configuration transforms the incident guided-wave into several separate segments, propagating in parallels independently and along each NRUC, which can be manipulated separately. This methodology grants a general solution to forge ferrite components in a multimode configuration, discussed in detail to corroborate the proposed generalized theory. Finally, two multimode components are studied and demonstrated for the first time as application examples for the proposed theory. Namely, a dual-mode circulator and a triple-mode gyrator are prototyped, fabricated, and measured, exhibiting an excellent agreement with simulation results that effectively validate the presented theoretical foundation in this work. [ABSTRACT FROM AUTHOR]

• An all-optical diode device is proposed based on a topological photonic crystal heterostructure. • The heterostructure supports a tunable nonreciprocal topological edge mode with a perfect transmission. • The TES mode can be tuned by adjusting the incident angle of the input light in the linear regime. • The structure is used as a nonlinear all-optical diode by adjusting the intensity at a given angle of incidence. • The system acts as an all-optical diode in linear and nonlinear regimes. Here, we propose an all-optical diode device based on a topological photonic crystal heterostructure composed of two one-dimensional photonic crystals with a thin Weyl semimetal layer between them. An all-optical diode, a nonreciprocal device that allows perfect transmission in one direction and prohibits it in the opposite direction, is widely used in optical communication, all-optical signal processing, and information technology. The proposed structure can support a tunable nonreciprocal linear and nonlinear topological edge state with a perfect transmission. Unlike the photonic multilayer-based optical diodes, the proposed structure does not require strong nonlinearity and high spatial asymmetry. In the nonlinear regime, the transmission of the structure shows a bistable hysteresis loop with low switch-up and switch-down threshold intensities, which depend on the impinging direction of the input light. The topological edge state can be tuned by adjusting the incident angle of the input light in the linear regime. We can use the structure as a nonlinear all-optical diode by adjusting the intensity of the input beam at a given incident angle. [ABSTRACT FROM AUTHOR]

Parity-time-reversal symmetry (PTsymmetry), a symmetry for the combined operations of space inversion (P) and time reversal (T), is a fundamental concept of physics and characterizes the functionality of materials as well asPandTsymmetries. In particular, thePT-symmetric systems can be found in the centrosymmetric crystals undergoing the parity-violating magnetic order which we call the odd-parity magnetic multipole order. While this spontaneous order leavesPTsymmetry intact, the simultaneous violation ofPandTsymmetries gives rise to various emergent responses that are qualitatively different from those allowed by the nonmagneticP-symmetry breaking or by the ferromagnetic order. In this review, we introduce candidates hosting the intriguing spontaneous order and overview the characteristic physical responses. Various off-diagonal and/or nonreciprocal responses are identified, which are closely related to the unusual electronic structures such as hidden spin-momentum locking and asymmetric band dispersion., (Creative Commons Attribution license.)

A one-dimensional nonreciprocal structure comprising two asymmetric multilayers filled with magneto-optical dispersive media and a defect layer is designed. The nonreciprocal optical Tamm states (OTSs) are excited at the interface of the two asymmetric multilayer structure with an opposing external magnetic field. With the excitation of the nonreciprocal OTSs, the numerical results show that the waves can be transmitted and be reflected in one way. These nonreciprocal properties are affected by the layers thickness of the defect layer, the angles of incidence, and the externally applied magnetic fields. Owing to the inherent dispersive property of the magneto-optical media, our investigations show promising potential for the practical application of nonreciprocal structures. [ABSTRACT FROM AUTHOR]

Moving metasurfaces support-guided waves exhibiting unusual optical properties, including strong anisotropy, nonreciprocity, and hyperbolic dispersion. However, for these phenomena to be noticeable, high speeds are typically required, challenging their practical implementation. Here we show a viable route toward the realization of strongly nonreciprocal hyperbolic propagation in metasurfaces placed synthetically in motion through traveling-wave space–time modulation. In addition to nonreciprocal hyperbolic propagation, the proposed time-modulation scheme induces additional exotic opportunities for nanophotonic systems, such as efficient nonreciprocal frequency conversion and mode transfer. [ABSTRACT FROM AUTHOR]

A nonreciprocal transmission structure is designed using a one-dimension multilayer medium, which consists of two asymmetric structure filled with the electric–gyrotropic dispersive media. The total transmission coefficients have been deduced using the transfer matrix method. Numerical results further provided evidence for the occurrence of the nonreciprocal surface electromagnetic waves. These states are affected by the thickness of layers, incident angles, and the externally applied magnetic fields. Given that the electric–gyrotropic media are inherently dispersive, our investigations will contribute to the practical application of nonreciprocal structures. [ABSTRACT FROM AUTHOR]

In this work, a class of antisymmetrically biased ferrite-loaded substrate integrated waveguides (SIWs) is studied in detail along with the definition of three main regions of operation. With focus on one of those newly defined regions, a nonreciprocal mode waveguide (NRMW) is introduced for the first time and its related design procedure is explained and illustrated. Furthermore, a fundamental approach is proposed and devised for developing a fully integrated structure called nonreciprocal mode-converting waveguide (NRMCW). This ferrite-based device is capable of effectively converting TE10 mode into TE20 mode only in one direction, thereby suggesting that the original mode be preserved in the reverse direction. In other words, the mode conversion, in this case, is unidirectional, which has never been reported so far. To substantiate the usefulness of the proposed structure and physical mechanism, a class of circulators is designed, fabricated, and demonstrated on the basis of the introduced NRMCW, thus validating the formulated theory of NRMCW in this work and providing an application example of such devices. Both theoretical and experimental results are presented in support of the claims made in this work regarding the proposed circuit concept and its related foundation work. [ABSTRACT FROM AUTHOR]

Highlights • A novel infrared nonreciprocal absorbers. • The optical properties of the CdTe magneto-optical material are investigated. • The Lorentz-Drude equations of dielectric constant tensor can predict the optical properties of CdTe well. • Obvious nonreciprocal effect can be achieved. • Important use for the infrared detector and infrared absorption regulation. Abstract In this paper, a novel CdTe gratings structure is designed aimed at constructing omnidirectional infrared nonreciprocal absorbers at wavelength from 18 μm to 23 μm. CdTe is a commonly used semiconductor infrared film material, which is widely used in photovoltaic, infrared detection, fluorescence and other applications. The optical radiation characteristics of magneto-optical material CdTe are studied based on the Lorentz-Drude model, which is verified with the optical constants in handbook. The time-domain finite difference (FDTD) method was used to calculate the infrared radiation characteristics of CdTe gratings, and the electric field square modulus distribution with different wavelengths is presented. It is found that the nonreciprocal absorptivity is obvious as the incidence angle is 45° at the positive and negative angles. The effects of magnetic field strength, grating thickness, incidence angles on the optical properties, especially the non-reciprocity are analyzed in details. The numerical simulation results are useful to the thermal radiative design in infrared absorber and other optical instrument. [ABSTRACT FROM AUTHOR]

Photonic crystals containing graphene nanolayers have been attracting increasing attention due to their distinctive properties. In this paper, we present a theoretical analysis on the transmission properties of magneto-photonic crystals containing graphene nanolayers by using the transfer matrix method. The investigation shows that unidirectional defect modes with high transmittance can be achieved in the proposed structure, and broad flat-top photonic conduction bands (PCBs) can also be found between the graphene-induced photonic band gap and the Bragg gap. Furthermore, the study on the PCBs indicates that the relationship between the number of PCBs (n) and the period number of the structure (N) can be expressed as n = N − 1(N = 2,3,4...). And, new and unexpected photonic band gaps among PCBs are observed. The effects of chemical potential of graphene, thickness of defect layer, and incident angle on transmission properties are also discussed. The research results may provide a valuable reference for the design and fabrication of optical communication devices, such as isolators, switches, multichannel filters, and so on. [ABSTRACT FROM AUTHOR]

Abstract: The magneto‐optical properties of conduction electrons in InSb in Voigt geometry at oblique incidence angles are explored. In parallel magnetic field, the oblique incidence reflectance exhibits high nonreciprocity, while the transmittance remains reciprocal. This phenomenology, combined with the unique magnetoplasmonic properties of InSb (high electron mobility, low effective mass, and temperature‐tunable bulk plasma frequency), allows the design of a simple and high‐performance THz optical isolator that works directly with linearly polarized light. It is demonstrated that the isolation power of the device exceeds 35 dB with the insertion loss of only −6.2 dB. The simplicity of the isolator design is unmatched among the proposed THz isolator concepts to date. [ABSTRACT FROM AUTHOR]

By employing classic electromagnetic theory, we have theoretically investigated the properties of lateral shift (LS) in the interface between air and the gyrotropic medium (gyroelectric medium and gyromagnetic medium). The influence of the electromagnetic (EM) parameters, incident angle and thickness of the plate on the shift have also been analyzed. Due to the gyrotropic element of EM parameters, the numerical results have shown that the LS is nonreciprocal with the incident angle, EM parameters and thickness of the plate. [ABSTRACT FROM AUTHOR]

Compared with reciprocal optical materials, nonreciprocal materials can break the time reversal and detailed balance due to special nonreciprocal effect, while how its characteristics performing on infrared wavelength have not been paid enough attention. In this paper, the optical properties of three magneto-optical materials was investigated in infrared band, that are n-InAs, GaAs, HgCdTe, based on Finite Difference Time Domain (FDTD) method. The equations of dielectric constant tensor are present and the effect of magnetic field intensity and frequency has been studied in detail. Additionally, the effect of incidence angle at positive and negative directions to the nonreciprocal absorptivity is also investigated. It is found that the nonreciprocal effect is obvious in infrared wavelength, and the nonreciprocal effect could adjust the absorption characteristic, thus be able to tune the absorption for the specific frequency of incident light. In addition to modeling the directional radiative properties at various angles of incidence, the absorption peaks of three materials under different incident angles are also calculated to understand the light absorption and to facilitate the optimal design of high-performance photovoltaic and optical instrument. [ABSTRACT FROM AUTHOR]

This paper is focused on the analysis of line junctions obtained as a cascade of dielectric and ferrite guides of arbitrary cross-section. The main application of such structures is nonreciprocal devices such as isolators, circulators, or phase shifters. The efficient finite element/mode-matching approach is proposed to the analysis of such structures. In this approach, the finite element method is applied to determine propagation coefficients and field distributions in cross-sections of the structure. Then using mode-matching technique the scattering parameters of investigated junction are calculated. Since, all the field integrals required in mode-matching are evaluated in the pre-processing stage of finite element method, only small numerical effort is required to calculate scattering parameters of the junction. The numerical efficiency of proposed approach is examined for different geometries of longitudinally magnetized shielded ferrite coupled line junction. Obtained results are compared with the ones calculated using commercial software and presented in literature. A very good agreement is achieved. [ABSTRACT FROM PUBLISHER]

Herein, we present a floating 2-port nonreciprocal negative capacitance (NCAP) circuit that employs a unilateral gain boosting technique by including an asymmetric cross-coupled differential cascode transistor pair. The proposed circuit provides an asymmetric gain characteristic. The forward gain ( S21 ) is increased at the cost of the backward gain ( S12 ). The technique not only provides a boosted forward gain but also stable operation resulting from this reduced backward gain. We further investigate the stability of the NCAP circuit in terms of the output resistances of the current sources in the circuit. The proposed NCAP circuit was implemented in IBM 7RF 180-nm CMOS technology and was designed to have a supply voltage of 3 V and a current of 10 mA. The S-parameter measurements showed a self-resonance frequency of 2.25 GHz. The maximum S21 was −0.2 dB at 1 GHz. In the frequency range from 0.5 to 1.5 GHz, the capacitance was approximately −4 pF, and the difference between S21 and S12 was 8.7–9.6 dB. The size of the core chip was 150 \times 190~\mu \textm^2 . [ABSTRACT FROM AUTHOR]

The aim of this paper is the investigation of nonreciprocal phenomena in anisotropically loaded 2-D periodic structures. For this purpose, our well-established 2-D curvilinear finite difference frequency domain method is combined with periodic boundary conditions and extended toward the eigenanalysis of periodic structures loaded with both isotropic and general anisotropic materials. The periodic structures are simulated in a 2-D domain, while uniformity is considered along the third axis. The propagation constant along the third axis can either be zero (in-plane-propagation) or nonzero (out-of-plane propagation). Particular effort was devoted to the identification of the appropriate irreducible Brillouin zone to be scanned during the eigenanalysis. It was herein realized that similar to geometrically artificial crystal anisotropy, the wave propagation directional asymmetries modify the irreducible Brillouin zone in the microwave regime as well. Both gyrotropic and particularly magnetized ferrite as well as full tensor anisotropic (arbitrarily biased ferrite) material loadings are investigated through the eigenanalysis of different periodic structures, including strip grating. Interesting nonreciprocal backward wave and unidirectional phenomena are justified as expected. [ABSTRACT FROM PUBLISHER]

Nonreciprocal spin wave propagation, induced by placing a neighboring metallic nonmagnetic layer, has been studied in metallic ferromagnetic thin films. The structure consists of a set of coupled microstrip transmission lines acting as antennas placed over a thin Ni80Fe20 layer. Nonreciprocal propagation of magnetostatic surface waves (MSSWs) has been observed. The nonreciprocal effect is evaluated by the amplitude ratio and the phase difference of the MSSWs traveling in opposite directions. By investigating the correlation between the device structure and the nonreciprocal effects, a maximum of −26.0 dB of the amplitude ratio and −180.0° phase difference were obtained. These results can be applied to optimize the nonreciprocal device. [ABSTRACT FROM PUBLISHER]

Magnetic nanowired substrates (MNWS) have been used for the fabrication of a planar nonreciprocal microstrip device. It shows a differential phase shift of 300 degrees\cdotcm^-1 at Ka-band without requiring the application of a dc bias magnetic field, and making it suitable for miniaturized gyrator applications. The nonreciprocal operation is achieved by loading the device with nanowires of different ferromagnetic materials. This allows to control the phase velocity of the microwave signal passing through the device by virtue of the spatial variation of the MNWS permeability. The measured microwave performances of the device have been reproduced with excellent accuracy using a proposed analytical model based on an effective medium theory and useful for the prediction of further tunable capabilities. [ABSTRACT FROM AUTHOR]

Surface magnetoplasmons on a single semiconductor–dielectric interface in a transverse static magnetic flux have been modelled. The dispersion diagrams exhibit nonreciprocal behaviour for the forward and reverse propagation as expected, but the effect of the permittivity of the dielectric is shown for the first time. The elliptical polarization of the electric field in both media, near the interface, above and below the EWR frequency, for both directions of propagation is computed. The results have implications for the development of miniature isolators and phase shifters at millimetric and submillimetric wavelengths. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 505–509, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20017 [ABSTRACT FROM AUTHOR]

The normal-mode approach is used to design stripline-type ferrite coupled line circulators with alumina as a substrate and ferrite as a superstrate. The measurements that are taken clearly demonstrate the nonreciprocal behavior of these devices, with an average insertion loss of 5 dB and an isolation of -12 dB. It is found that the three-port circulator has a broader bandwidth (9–14 GHz) than that of the four-port circulator (9–12 GHz), and the hybrid coupler has been identified as the bottleneck in the latter. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 173–179, 2003. [ABSTRACT FROM AUTHOR]

The propagation characteristics of a microstrip line printed on a YIG/GGG film are analyzed by the spectral-domain approach for arbitrary orientation of the bias magnetic field. The nonreciprocal property of the YIG film is explored by studying the characteristics of the forward and backward wave. The change in differential phase shift with frequency obtained due to arbitrary orientation of the bias magnetic field finds application in microwave signal processing. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 29–35, 2002. [ABSTRACT FROM AUTHOR]

• The electrical conductivities and dielectric constants of graphene based on different theoretical models are discussed. • A novel magneto-plasma structure has been proposed for achieving high absorptivity. • The non-reciprocal optical properties effect has been enhanced. • The physical mechanisms of the enhancement for nonreciprocal effect are discussed. • The model is useful for design and application in nonreciprocal optical devices. We present a theoretical study of the magnetic field dependence of the nonreciprocal absorption effect for composite microstructure. We analyses and summarizes the relevant conductivity calculation models of graphene, and discusses and compares the electrical conductivities and dielectric constants of graphene based on different theoretical models. Moreover, the external magnetic field applied model and the non-magnetic field applied model are compared in details, the most suitable calculation model has finally chosen. And the influence of the chemical potential on the refractive index of graphene was compared and discussed under the condition of an external magnetic field. Furthermore, we propose a nonreciprocal effect enhanced magneto-optical composite microstructure using graphene and analyze the effect of grating height, grating filling ratio, incidence angle and magnetic field intensity on the nonreciprocal absorptance, in this work. It is found that graphene can effectively enhance the nonreciprocity phenomenon in the wavelength range, and the absorptance can also be greatly improved. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the Green's dyadics for a homogeneous bianisotropic medium where the material dyadics are of the form \documentclass{minimal} \begin{document} \thispagestyle{empty} $\overline{\overline{\mu}}=\tau\overline{\overline{\epsilon}}{}^{T}+\mathbf{ab}$ \end{document} , \documentclass{minimal} \begin{document} \thispagestyle{empty} $\overline{\overline{\xi}}={\mathbf{x}}\times\overline{\overline{I}}+\xi\mathbf{bb}$ \end{document} , and \documentclass{minimal} \begin{document} \thispagestyle{empty} $\overline{\overline{\zeta}}={\mathbf{z}}\times\overline{\overline{I}}+\zeta\mathbf{aa}$ \end{document} . We will show that the Helmholtz determinant operator still can be factorized for this medium. The scalar Green's function of this operator cannot be derived in closed form, but can be expressed as a two-dimensional inverse Fourier transformation. Within the paper, we make extensive use of dyadic analysis. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 21: 304–309, 1999. [ABSTRACT FROM AUTHOR]

The possibility of finding an analytic Green dyadic expression for a class of bianisotropic media, defined by the relations $\bar{\bar{\epsilon}}=\tau\bar{\bar{\mu}}{}^{T}$, $\bar{\bar{\xi}}={\bf{x}}\times \bar{\bar{I}} +\xi{\bf{u}}{\bf{u}}$, and $\bar{\bar{\zeta}}={\bf{z}}\times \bar{\bar{I}} +\zeta{\bf{u}}{\bf{u}}$ between the medium parameter dyadics, is studied. It is shown that the determinant of the dyadic Helmholtz operator, an operator of fourth order, can be expressed as a product of two second-order operators. A method for finding the solution for the Green dyadic in the form of infinite series in terms of powers of the dimensionless parameter ξζ/μoεo is given. For small values of the parameter, a two-term approximation is seen to take a simple analytic form. As an Appendix, another approach through the Fourier transformation is briefly discussed. Dyadic formalism is applied throughout in the analysis. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 19: 216–221, 1998. [ABSTRACT FROM AUTHOR]

Nonreciprocal magnetostatic wave propagation in micro-patterned Ni80Fe20 thin film has been investigated. The nonreciprocal devices consist of a set of coupled microstrip transmission lines acting as antennae on the top of the micro-patterned Ni80Fe20 films. The Ni80Fe20 films were structured into an array of rectangular prisms. Nonreciprocal wave propagation was observed in the patterned Ni80Fe20 film. Compared to the control device with a continuous Ni80Fe20 film, the micro-patterned Ni80Fe20 films led to a weaker non-reciprocity. [ABSTRACT FROM PUBLISHER]