Nonreciprocal Components Research Articles

Noise performance analysis of PT-symmetric non-reciprocal transmission systems

Non-reciprocity is a crucial concept in the field of signal transmission and processing as it protects sensitive elements from the effects of feedback signal. The non-reciprocal components based on ferrite materials are bound to show shortcomings due to incompatibility with chip-level ICs. In recent years, parity-time (PT)-symmetric non-reciprocal transmission in electronic systems has been proposed and analyzed. Here, we propose the simplified noise analysis model based on a PT-symmetric non-reciprocal transmission system. And we verify the theoretical noise model by simulation analysis and experimental demonstrations. The experimental result shows that the noise figure of the proposed PT-symmetric non-reciprocal transmission device is 7.5 dB because of the employment of the active amplifier. This work establishes a noise performance analysis framework, providing guidance for the development of lossless and miniaturized applications of non-reciprocal components.

Nonreciprocal reflection based on asymmetric graphene metasurfaces.

We propose a scheme to achieve controllable nonreciprocal behavior in asymmetric graphene metasurfaces composed of a continuous graphene sheet and a poly crystalline silicon slab with periodic grooves of varying depths on each side. The proposed structure exhibits completely asymmetric reflection in opposite directions in the near-infrared range, which is attributed to the pronounced structural asymmetry and its accompanying nonlinear effects. The obtained nonreciprocal reflection ratio, reaching an impressive value of 21.27 dB, combined with a minimal insertion loss of just -0.76 dB, highlights the remarkable level of nonreciprocal efficiency achieved by this design compared to others in its category. More importantly, the proposed design can achieve dynamic tunability by controlling the incident field intensity and the graphene Fermi level. Our design highlights a potential means for creating miniaturized and integratable nonreciprocal optical components in reflection mode, which can promote the development of the integrated isolators, optical logic circuits, and bias-free nonreciprocal photonics.

Hydrodynamics of an odd active surfer in a chiral fluid

We theoretically and computationally study the low-Reynolds-number hydrodynamics of a linear active microswimmer surfing on a compressible thin fluid layer characterized by an odd viscosity. Since the underlying three-dimensional fluid is assumed to be very thin compared to any lateral size of the fluid layer, the model is effectively two-dimensional. In the limit of small odd viscosity compared to the even viscosities of the fluid layer, we obtain analytical expressions for the self-induced flow field, which includes non-reciprocal components due to the odd viscosity. On this basis, we fully analyze the behavior of a single linear swimmer, finding that it follows a circular path, the radius of which is, to leading order, inversely proportional to the magnitude of the odd viscosity. In addition, we show that a pair of swimmers exhibits a wealth of two-body dynamics that depends on the initial relative orientation angles as well as on the propulsion mechanism adopted by each swimmer. In particular, the pusher–pusher and pusher–puller-type swimmer pairs exhibit a generic spiral motion, while the puller–puller pair is found to either co-rotate in the steady state along a circular trajectory or exhibit a more complex chaotic behavior resulting from the interplay between hydrodynamic and steric interactions. Our theoretical predictions may pave the way toward a better understanding of active transport in active chiral fluids with odd viscosity, and may find potential applications in the quantitative microrheological characterization of odd-viscous fluids.

Tunable magnetless optical isolation with twisted Weyl semimetals.

Weyl semimetals hold great promise in revolutionizing nonreciprocal optical components due to their unique topological properties. By exhibiting nonreciprocal magneto-optical effects without necessitating an external magnetic field, these materials offer remarkable miniaturization opportunities and reduced energy consumption. However, their intrinsic topological robustness poses a challenge for applications demanding tunability. In this work, we introduce an innovative approach to enhance the tunability of their response, utilizing multilayered configurations of twisted anisotropic Weyl semimetals. Our design enables controlled and reversible isolation by adjusting the twist angle between the anisotropic layers. When implemented in the Faraday geometry within the mid-IR frequency range, our design delivers impressive isolation, exceeding 50 dB, while maintaining a minimal insertion loss of just 0.33 dB. Moreover, the in-plane anisotropy of Weyl semimetals eliminates one or both polarizers of conventional isolator geometry, significantly reducing the overall dimensions. These results set the stage for creating highly adaptable, ultra-compact optical isolators that can propel the fields of integrated photonics and quantum technology applications to new heights.

Ferrite-Based Multiport Circulators With RF Co-Designed Bandpass Filtering Capabilities

This article reports on the RF design and practical development of multiport circulators with RF co-designed bandpass filtering functionality. The proposed bandpass filter/circulator (BPFC) concept is based on a hybrid implementation approach, where dual-mode non-reciprocal ferrite-based resonators (FBRs) are cascaded with microwave resonators and mixed-electromagnetic (EM) couplings. In this manner, highly selective bandpass filtering transfer functions are created in the direction of propagation, and high RF signal cancellation is obtained in the reverse direction. A design methodology using coupled-resonator-based synthesis is proposed to facilitate the design of these components using well-known filter design techniques. Various electromagnetically simulated and synthesized examples are presented to demonstrate the operating principles of the BPFC approach alongside its applicability to high-order filtering responses. The BPFC concept is further expanded to the realization of multiport non-reciprocal components. For proof-of-concept demonstration, four multiport prototypes were designed, manufactured, and measured at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$</tex-math> </inline-formula> -band.

Optimizing performance for an on-chip stimulated Brillouin scattering-based isolator

Non-reciprocal optical components such as isolators and circulators are crucial for preventing catastrophic backreflection and controlling optical cross talk in photonic systems. While non-reciprocal devices based on Brillouin intermodal transitions have been experimentally demonstrated in chip-scale platforms, harnessing such interactions has required a suspended waveguide structure, which is challenging to fabricate and is potentially less robust than a non-suspended structure, thereby limiting the design flexibility. In this paper, we numerically investigate the performance of a Brillouin-based isolation scheme in which a dual-pump-driven optoacoustic interaction is used to excite confined acoustic waves in a traditional ridge waveguide. We find that acoustic confinement, and therefore the amount of Brillouin-driven mode conversion, can be enhanced by selecting an appropriate optical mode pair and waveguide geometry of two arsenic-based chalcogenide platforms. Further, we optimize the isolator design in its entirety, including the input couplers, mode filters, the Brillouin-active waveguide as well as the device fabrication tolerances. We predict such a device can achieve 30 dB isolation over a 38 nm bandwidth when 500 mW pump power is used; in the presence of a ± 10 n m fabrication-induced width error, such isolation can be maintained over a 5–10 nm bandwidth.

Bulk generalized Dzyaloshinskii-Moriya interaction in PT -symmetric antiferromagnets

The Dzyaloshinskii-Moriya interaction (DMI) in magnetic materials plays an important role in spintronics, giving rise to chiral spin textures such as the nucleation and propagation of domain walls and skyrmions. The necessary ingredient for the emergence of the DMI is the lack of inversion symmetry combined with elements with strong spin-orbit coupling. We report on a first-principles investigation of generalized DMIs in bulk centrosymmetric crystals with noncentrosymmetric local sublattices, where we consider a prototype family of $\mathcal{PT}$-symmetric antiferromagnets, including, ${\mathrm{Mn}}_{2}\mathrm{Au}$, ${\mathrm{MnPd}}_{2}$ and MnCuAs in the tetragonal and orthorhombic phases. We employ a Green's function approach to calculate the interatomic relativistic exchange coupling which can, in turn, determine the sublattice elements of the generalized fifth-order DMI tensor ${D}_{\ensuremath{\alpha}\ensuremath{\beta},\ensuremath{\gamma}}^{s{s}^{\ensuremath{'}}}$. We demonstrate that the breaking of the local mirror symmetry and the resulting local Rashba-type spin-momentum locking yield local DMIs with opposite signs on the two antiparallel sublattices. We present numerical results and provide analytical expressions for the magnon dispersion in the presence of the sublattice DMI and show that the intra- (inter-) sublattice DMIs result in identical (opposite) contributions to the nonreciprocal components of the two low-frequency antiferromagnetic magnon modes.

Spatiotemporally Modulated Gyrators with Extended Bandwidth through Dual-Sideband Operation

One of the major challenges in the design of nonreciprocal devices is the application of magnetic biasing. This problem has motivated a flurry of work for the development of magnetless nonreciprocal devices, with spatiotemporal modulation being one of the most promising approaches to this end. The most fundamental nonreciprocal component is the gyrator, which can be the building block of other nonreciprocal components, like ciculators and isolators. Spatiotemporally modulated (STM) gyrators are typically based on a pair of frequency converters with different modulation phases, connected through a linear time-invariant network. Such gyrators are usually designed to operate with a single modulation sideband. In this paper we argue that this approach is suboptimal and show how adding just one more sideband can increase the bandwidth by $40\mathrm{%}$ with a lower modulation frequency and the same modulation amplitude. We present an implementation of the proposed approach based on a double-balanced circuit with Wheatstone bridges of varactors, which provides large isolation between the input signal and the sidebands. We provide a theoretical and an experimental analysis of the circuit with excellent agreement to each other. In addition to introducing a topology of STM gyrators with improved bandwidth compared with existing designs, our results highlight a potential connection between the bandwidth of STM devices and their harmonic order, which might also find applications in other STM systems, like isolators, circulators, and photonic topological insulators.

Nonreciprocal photonic management for photovoltaic conversion: design and fundamental efficiency limits

Significant progress in the development of nonreciprocal optical components with broken Kirchhoff symmetry paves the way for increasing the photovoltaic (PV) conversion efficiency beyond the Shockley–Queisser limit due to reuse of emitted photons. Recent papers have analyzed the PV converter with several or an infinite number of multijunction cells, in which the cells are coupled via nonreciprocal filters (optical diodes) in such a way that the light emitted by one cell is absorbed by another cell. We proposed and investigated a single cell converter with nonreciprocal external photon recycling, which provided reabsorption and reuse of the emitting light by the same cell. We considered properties of photons in the sunbeam in terms of ergodicity, disorder, energy availability, information entropy, and coherence, and established fundamental limitations imposed by endoreversible thermodynamics on conversion efficiency at maximal power output. Our results show that the nonreciprocal converter with an ideal multijunction cell can approach the Carnot efficiency, whereas operating exactly at the Carnot limit requires an infinite number of photon recycling processes. This requirement resolves the famous thermodynamic paradox of the optical diode because any small dissipation in the cell or optical system enhanced by infinite recycling will stabilize the converter operation below the Carnot limit. We generalized endoreversible thermodynamics to photonic distributions with nonzero chemical potential and derived the limiting efficiency of the nonreciprocal single-junction PV converter. The performance of this converter with available GaAs solar cells was evaluated.

Temporally modulated metamaterial based on a multilayer graphene structure

The recently developed concept of time-varying metamaterials paves the way for advanced methods of electromagnetic property modulation, such as magnet-free isolators, frequency converters, and other nonreciprocal photonic components. Here, we analyze the metamaterial based on the periodically arranged temporally modulated graphene layers via a steplike graphene Fermi level. The material properties are described by the effective medium theory. The electromagnetic wave temporal scattering phenomenon caused by rapid steplike graphene Fermi level switching is considered. It is demonstrated that the frequency of scattered waves increases as the Fermi level grows rapidly and vice versa. The relation between the amplitudes of forward- and backward-scattered waves is found using the Laplace transform technique. The proposed concept allows us to efficiently generate frequency harmonics under instant switching of the graphene Fermi level at a few meV. Our investigation provides a basement for the realization of temporally modulated multilayer structures based on functional tunable materials as power-efficient frequency converters.

Generalized Theory of Concurrent Multimode Reciprocal and/or Nonreciprocal SIW Ferrite Devices

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.

Non-Hermitian elastic waveguides with piezoelectric feedback actuation: non-reciprocal bands and skin modes

In this work, we investigate non-Hermitian (NH) elastic waveguides with periodically applied proportional feedback efforts, implemented through piezoelectric sensors and actuators. Using one-dimensional spectral models for longitudinal motion, it is shown that dispersion diagrams of this family of structures exhibit non-reciprocal imaginary frequency components, manifesting as wave attenuation or amplification along opposite directions for all Bloch bands (BBs). The effects of positive and negative proportional feedback, as well as local and non-local actuation are investigated. Overall, switching the sign of the feedback effort inverts the amplification direction, while increasing the degree of non-locality produces splitting of the BBs into multiple bands with interchanging non-reciprocal behavior. Furthermore, skin modes localized at the boundaries of finite domains are investigated and successfully predicted by the winding number of the complex dispersion bands. These results contribute to recent efforts in designing metamaterials with novel properties associated with the physics of non-Hermitian systems, which may find fruitful technological applications relying on vibration and noise control, wave localization, filtering and multiplexing.

Non-Magnetic Non-Reciprocal Microwave Components — State of the Art and Future Directions

Non-reciprocal components such as circulators, isolators and gyrators find utility in numerous microwave wireless applications, including high-power transmitters, simultaneous transmit-and-receive communication and radar systems, and emerging cryogenic quantum computing implementations. Today, such components are implemented using ferrite materials, which lose their reciprocity under the application of an external magnetic field. However, ferrite materials are incompatible with semiconductor integrated-circuit fabrication processes, and therefore ferrite non-reciprocal components are difficult to miniaturize to chip scales, rendering them bulky and expensive. This has motivated significant research into non-magnetic non-reciprocal components over the past 50 years. In recent years, this research has been invigorated by breakthroughs in time-modulated non-reciprocal components, and their integration into silicon integrated circuits. This paper reviews the history of non-reciprocal electronics, surveys recent research results in the area, and describes outstanding directions for future research.

A Review of Nonmagnetic Nonreciprocal Electronic Devices: Recent advances in nonmagnetic nonreciprocal components

Reciprocity is an underlying symmetry within a physical system that dates back to the work of Green in electrostatics in 1828 [1] . Later on, through the works of Helmholtz, Rayleigh, and Lorentz, reciprocity theorems were developed in different fields, such as optics, acoustics, elastodynamics, and electromagnetics [2] , [3] . The electromagnetic reciprocity theorem states that, for a system with symmetrical permittivity and permeability tensors, which is passive, linear, and time invariant, the transmission and reception between two points in space are identical in opposite directions regardless of any spatial asymmetry within the channel between them.

Electromagnetic Isolation Induced by Time-Varying Metasurfaces: Nonreciprocal Bragg Grating

In this letter, we propose a magnet-less non-reciprocal isolating system based on time-varying metasurfaces. Two parallel time-varying metasurfaces, one for frequency up-conversion and one for down-conversion by the same amount, are used for realizing a region of space where incident waves from opposite directions experience an opposite Doppler frequency shift. As a result, any device within this region becomes sensitive to the illumination direction, exhibiting a different scattering response from opposite directions and thus breaking reciprocity. Very importantly, thanks to the opposite frequency shift of the metasurfaces, the frequency of the transmitted electromagnetic field is the same as for the incident one. Here, we demonstrate this general approach by using a Bragg grating as the device between the time-varying metasurfaces. The combined structure of the metasurfaces and the grating exhibits different transmission and reflection properties for opposite illumination direction, thereby realizing an isolator. More broadly, this letter presents a strategy for converting any conventional electromagnetic device to a non-reciprocal one by placing it between two time-varying metasurfaces. This approach opens the door to several new non-reciprocal components based on thin and lightweight metasurfaces, which are simpler to realize compared to their volumetric counterparts.

Broadband and giant nonreciprocity at the subwavelength scale in magnetoplasmonic materials

We unveil a previously overlooked wave propagation regime in magnetized plasmonic (gyrotropic) materials with comparable plasma and cyclotron frequencies, which enables a giant and broadband (nondispersive) nonreciprocal response. We show that this effect is due to a natural form of dispersion compensation that ultimately originates from the subtle implications of the principle of causality for gyrotropic plasmonic media, which allows the existence of a low-loss frequency window with anomalous nonmonotonic dispersion for the extraordinary mode. This is in stark contrast with conventional nongyrotropic passive materials, for which the frequency derivative of the permittivity dispersion function is always positive in low-loss regions. These findings pave the way for superior nonreciprocal components in terms of bandwidth of operation and compactness, with orders-of-magnitude reductions in size. As a relevant example, we consider indium antimonide (InSb) to theoretically demonstrate a deeply subwavelength, broadband, THz isolator operating under moderate magnetic bias and at room temperature.

Integrated Nonreciprocal Photonic Devices With Dynamic Modulation

Nonreciprocal components, such as isolators and circulators, are crucial components for photonic systems. In this article we review theoretical and experimental progress towards developing nonreciprocal photonic devices based on dynamic modulation. In particular, we focus on approaches that operate at optical wavelengths and device architectures that have the potential for chip-scale integration. We first discuss the requirements for constructing an isolator or circulator using dynamic modulation. We review a number of different isolator and circulator architectures, including waveguide and resonant devices, and describe their underlying operating principles. We then compare these device architectures from a system-level performance perspective, considering how their figures of merit, such as footprint, bandwidth, isolation, and insertion loss scale with respect to device parameters.

Multi-Watt, 1-GHz CMOS Circulator Based on Switched-Capacitor Clock Boosting

There has been significant recent progress in the implementation of integrated non-reciprocal components based on linear periodically time-varying (LPTV) circuits. Nevertheless, integrated circulators still require a leap forward in power handling, clock power consumption, and insertion loss (IL) to become compelling compared with ferrite circulators or integrated reciprocal alternatives, such as the electrical-balance duplexer (EBD). This article introduces three innovations: 1) a new switched-capacitor clock-boosting scheme; 2) high-Bragg-frequency quasi-distributed transmission lines based on periodically loaded inductors; and 3) a new gyrator based on switched partially reflecting t-lines—which enable significant performance improvement for integrated circulators and for LPTV circuits more broadly. These are showcased in a 1-GHz 180-nm SOI CMOS circulator that exhibits 2.1-/2.6-dB TX-ANT/ANT-RX IL (0.3 dB better than prior art), +34-dBm TX-ANT P1 dB (2.5 $\times $ or 4 dB better), and 40% lower chip area, all at 39-mW power consumption (4.4 $\times $ lower).

Acoustoelectric Non-Reciprocity in Lithium Niobate-on-Silicon Delay Lines

Lamb wave delay lines with acoustoelectri-cally-induced non-reciprocity are demonstrated in suspended lithium niobate-on-silicon waveguides for the first time. An electric current is fed through the silicon layer in the same axis as the piezoelectrically-transduced acoustic waves which are attenuated or amplified depending on the direction of the energy exchange with drifting electrons (i.e. acoustoelectric (AE) effect). Therefore, the insertion loss (IL) and non-reciprocity of the delay line is adjustable by controlling the current bias which varies the electron drift velocity and the subsequent momentum transfer. Proof-of-concept delay lines in the range of 600 MHz to 700 MHz are demonstrated with a fractional bandwidth as high as 2.8% and AE gain as high as 5.6 dB resulting in ~20 dB of non-reciprocity. These non-reciprocal components could offer a monolithic and dynamically-tunable solution to the numerous issues that arise from the increasing congestion and interferences in the telecommunication spectrum and suggests the possibility of developing fully-switchable low-IL delay lines through design/fabrication optimizations.

Sub‐Wavelength Passive Optical Isolators Using Photonic Structures Based on Weyl Semimetals

AbstractThe paper presents the design of sub‐wavelength high‐performing nonreciprocal optical devices using recently discovered magnetic Weyl semimetals. These passive bulk topological materials exhibit anomalous Hall effect which results in magneto‐optical effects that are orders of magnitude higher than those in conventional materials, without the need of any external magnetic bias. Two optical isolators of both Faraday and Voigt geometries are designed. The isolators have dimensions that are reduced by three orders of magnitude compared to conventional magneto‐optical configurations. The designed structures demonstrate that the magnetic Weyl semimetals may open up new avenues in photonics for the design of various nonreciprocal components.