Nonreciprocal Components Research Articles

Non-reciprocal electronics based on temporal modulation

In general, reciprocity requires that signals travel in the same manner in both forward and reverse directions. It governs the behaviour of the majority of electronic circuits and components, imposing severe restrictions on how they operate. Components that violate reciprocity, such as gyrators, isolators and circulators, are, however, of use in many different electronic applications. Non-reciprocal electronic components have typically been implemented using ferrites, but such magnetic materials cannot be integrated in modern semiconductor fabrication processes and magnetic non-reciprocal components remain bulky and expensive. Creating non-reciprocal components without the use of magnetic materials has a long history, but has recently been reinvigorated due to advancements in semiconductor technology. Here we review the development of non-reciprocal devices and the development of non-magnetic non-reciprocal electronics, focusing on devices based on temporal modulation, which arguably exhibit the greatest potential. We consider approaches based on temporal modulation of permittivity and conductivity, as well as hybrid acoustic–electronic components, which have applications including high-power transmitters for communications, simultaneous transmit and receive radars, and full-duplex wireless radios. We also explore superconducting non-reciprocal components based on temporal modulation of permeability for potential applications in quantum computing and consider the key future challenges in the field. This Review Article examines the development of non-magnetic non-reciprocal electronics with a focus on devices based on temporal modulation, including approaches based on temporal modulation of permittivity and conductivity, as well as superconducting components for applications in quantum computing.

A 210-GHz Magnetless Nonreciprocal Isolator in 130-nm SiGe BiCMOS Based on Resistor-Free Unidirectional Ring Resonators

Nonreciprocal components such as circulators, isolators, and gyrators play vital roles in modern communication systems. However, all of them are limited to 0.1 terahertz (THz) due to their poor performances in terms of linearity, loss, and noise at high frequency, making them not amenable for the potential sub-THz/THz operation. In this letter, a 210-GHz nonreciprocal isolator based on the resistor-free unidirectional ring resonators is implemented in a 130-nm SiGe BiCMOS process ( $f_{T}/f_{\mathrm {max}} = 300$ /500 GHz). Thanks to the proposed resistor-free ring resonators, the isolator achieves 1.40-dB loss, 6.7-dB noise figure (NF)/unit, 21.2-dB isolation, and superior linearity. Even compared with the nonreciprocal components operating at a much lower frequency, this structure also exhibits a good performance.

Theory and Design of Multifunctional Space-Time Metasurfaces

Integrating multiple functionalities into a single metasurface is becoming of great interest for future intelligent communication systems. While such devices have been extensively explored for reciprocal functionalities, in this work, we integrate a wide variety of nonreciprocal applications into a single platform. The proposed structure is based on spatiotemporally modulated impedance sheets supported by a grounded dielectric substrate. We show that, by engineering the excitation of evanescent modes, nonreciprocal interactions with impinging waves can be configured at will. We demonstrate a plethora of nonreciprocal components such as wave isolators, phase shifters, and circulators, on the same metasurface. This platform allows switching between different functionalities only by modifying the pumping signals (harmonic or non-harmonic), without changing the main body of the metasurface structure. This solution opens the door for future real-time reconfigurable and environment-adaptive nonreciprocal wave controllers.

Microwave non-reciprocal coplanar directional coupler based on ferrite materials

ABSTRACTMagnetized ferrites are anisotropic materials used in passive non-reciprocal components. One of the main applications of ferrites at microwave frequencies is the isolation effect. In this work, the non-reciprocal propagation in a ferrite coplanar coupler is studied from simulation results. The proposed structure exhibits a low insertion loss less than 1 dB, and return loss better than 20 dB, with significant non-reciprocal behavior for through propagation. The design of the non-reciprocal coplanar coupler, based on a magnetized transversally ferrite as substrate dielectric material, is presented. The numerical study allows to describe the component physical behavior. As results, a miniature coupler at 12.50 GHz with a non-reciprocal effect in direct access is better than 35 dB has been designed and simulated.

Comparative investigation of two-dimensional materials for the design of non-reciprocal antennas in terahertz band

Two-dimensional materials have already demonstrated their potentials in the making of non-reciprocal components. In this paper, we compared the performance of terahertz non-reciprocal antennas made up of magnetized graphene, black phosphorus, and hybrid structure in a view to choose a suitable material for effective non-reciprocal THz antennas. A classical patch antenna is used as the reference antenna to effect the comparisons. The performances of these antennas are analyzed and it was found that the proposed strategy of hybridization of graphene and BP shows better electromagnetic performance with their counterparts. The response of the antenna can be controlled conveniently by adjusting the chemical potential of graphene and it is significantly decreased by adjusting the electron doping of black phosphorus.

Direction reconfigurable nonreciprocal acousto-optic modulator on chip

Nonreciprocal components are essential in photonic systems for protecting light sources and for signal routing functions. Acousto-optic methods to produce nonreciprocal devices offer a foundry-compatible alternative to magneto-optic solutions and are especially important for photonic integration. In this paper, we experimentally demonstrate a dynamically reconfigurable nonreciprocal acousto-optic modulator at the telecom wavelength with a peak contrast of 8 dB and a 3 dB bandwidth of 1.1 GHz. The modulator can be arranged in a multitude of reciprocal and nonreciprocal configurations by means of an external RF input. The dynamic reconfigurability of the device is enabled by a new cross-finger interdigitated piezoelectric transducer that can change the directionality of the reciprocity-breaking acoustic excitation based on the phase of the RF input. The methodology we demonstrate here may enable new avenues for direction dependent signal processing and optical isolation.

Nonreciprocal metasurface with space\u2013time phase modulation

Creating materials with time-variant properties is critical for breaking reciprocity that imposes fundamental limitations on wave propagation. However, it is challenging to realize efficient and ultrafast temporal modulation in a photonic system. Here, leveraging both spatial and temporal phase manipulation offered by an ultrathin nonlinear metasurface, we experimentally demonstrated nonreciprocal light reflection at wavelengths around 860 nm. The metasurface, with travelling-wave modulation upon nonlinear Kerr building blocks, creates spatial phase gradient and multi-terahertz temporal phase wobbling, which leads to unidirectional photonic transitions in both the momentum and energy spaces. We observed completely asymmetric reflections in forward and backward light propagations over a large bandwidth around 5.77 THz within a sub-wavelength interaction length of 150 nm. Our approach highlights a potential means for creating miniaturized and integratable nonreciprocal optical components.

How Does Reciprocity Affect Undergraduate Student Orientation towards Stakeholders?

Nowadays, students are more aware of the impact of companies on their stakeholders and the need for properly handling their expectations to operationalize corporate social responsibility. Nevertheless, little is known about how certain individual traits may relate to their stance on the issue. This exploratory research contributes to stakeholder theory by analysing the effect of the individual’s decision-making process, including the consideration of their social preferences, on their orientation toward stakeholder management. Here, we draw upon a theoretical model for resource-allocation decision-making consisting of reciprocal and non-reciprocal components. Our data, from undergraduate students enrolled in different degrees, were collected through a questionnaire and two social within-subject experiments (ultimatum and dictator games). Thus, our results show that the presence of a reciprocal component when decisions are made is positively linked to an instrumental orientation toward stakeholders. In addition, a greater non-reciprocal component in the decision-making process corresponds to a more normative orientation.

Magnetic field effect on electrodeposition of CoFe2O4 nanowires

In this work, cobalt ferrite (CoFe2O4) magnetic nanowires have been electrodeposited with and without magnetic field into a commercial 100-nm-grade AAO template. For the magneto-electrodeposited CoFe2O4 nanowires, the XRD analysis emphasized the diminution in size of the diffracting crystallites. The SEM investigations exhibited that the magnetic field favors the filling of the nanowires by cobalt and iron elements. The AFM analysis revealed the reduction of the surface roughness. The VSM measurements showed a significant change in the coercivity and the squareness ratio of cobalt ferrite nanowire arrays. A variation between 1150 and 1331 Oe for the coercive field Hc, and from 0.30 to 0.39 for the squareness ratio Mr/Ms was observed. This ferrimagnetic nanocomposites could be used as a non-reciprocal passive components for magneto-optical and microwave devices.

Magnetless Circulators with Harmonic Rejection Based on N -Way Cyclic-Symmetric Time-Varying Networks

In photonics, circulators are three-port nonreciprocal components that allow unidirectional signal transmission from one port to another, in a cyclic rotating fashion. Magnetless circulators based on spatiotemporally modulated networks have recently been proposed as improvements over traditional designs, but these devices have their own shortcomings. The authors show that a suitable arrangement of $N$ nonlinear, time-varying unit cells with a gradient phase shift between their modulation signals can actually yield an effectively linear time-invariant nonreciprocal response. Such a circulator could enable $e.g.$ full-duplex communication, radar, and quantum computing.

Existence of high Faraday rotation and transmittance in magneto photonic crystals made by silica matrix doped with magnetic nanoparticles

This paper focuses on studying the potential of CoFe2O4-doped magnetic nanoparticles SiO2 / ZrO2 matrix to produce high-performance one-dimensional magnetophotonic crystals (MPC) and to solve the problem of integrating magneto-optical devices. Given the importance of the magneto-optical Faraday effecton most non-reciprocal optical components, we studied the influence of different 1D structures on Faraday rotations.The potential of these structures offers a wide range of applications in the field of miniaturized and integrated non-reciprocal devicessuch as isolators.

Design Algorithms of Driving-Induced Nonreciprocal Components

We utilize an effective Hamiltonian formalism, within the Floquet scattering framework, to design a class of driving-induced non-reciprocal components with {\it minimal} complexity. In the high driving-frequency limit, where our scheme is formally applicable, these designs demonstrate a leading order non-reciprocal performance which is inverse proportional to the driving frequency. Surprisingly, the optimal non-reciprocal behavior persists also in the slow driving regime. Our approach highlights the importance of physical loops in the design of these driven non-reciprocal components.

85–110-GHz CMOS Magnetic-Free Nonreciprocal Components for Full-Duplex Transceivers

Two CMOS nonreciprocal components: 1) an isolator and 2) a circulator are demonstrated at 100-GHz band for full-duplex transceivers for ultra-high-data-rate wireless communication. The proposed nonreciprocal structures are based on a time-domain modulation by signals at around one-sixth of the RF frequencies and spatial duplexing throughout their RF signal paths, demonstrating over 45-dB isolation in a bandwidth of 1.5 GHz over the tuning range of 85-110 GHz. In the presented isolator, two capacitive mixers together with a biasing network form a resonant type of wideband matching for lower loss. An improved delta topology is proposed for the circulator design which reduces the schematic complexity and chip area overhead. Implemented in a 65-nm CMOS with a chip area of 0.13 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 0.21 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively, both the isolator and the circulator achieve over 45-dB isolation and >10 dB return losses throughout the entire bandwidth. A maximum of 4.5- and 5.6-dB insertion losses (ILs) are achieved by the isolator and circulator, respectively.

Integrated Conductivity-Modulation-Based RF Magnetic-Free Nonreciprocal Components: Recent Results and Benchmarking

Achieving non-reciprocity and building nonreciprocal components through spatio-temporal modulation of material properties has attracted a lot of attention in the recent past as an alternative to the more traditional approach of exploiting Faraday rotation in magnetic materials. In this letter, we review recent research on spatio-temporal conductivity-modulation, which enables low-loss, small-footprint, wide-bandwidth and high-power-handling non-reciprocal components operating from radio frequencies (RF) to millimeter-waves (mm-waves) and integrated in a CMOS platform. Four generations of non-reciprocal circulators and circulator-based systems will be reviewed. We will also discuss metrics of performance that are important for wireless applications and standards, and introduce a new antenna (ANT) interface efficiency figure of merit ($\eta_{ANT}$) to enable a fair comparison between various types of antenna interfaces.

Doped Barium Hexaferrite Films for Self-Biased Nonreciprocal Components in the Q-/V-Band

Doped barium hexaferrite films prepared on alumina substrates by means of the sol-gel method, intended for utilization in self-biased nonreciprocal components, are presented in this letter. To cover a broad range of potential applications, the ferromagnetic resonant frequency (FMRF) of the material is controlled by substituting iron for scandium and aluminum. The films are deposited on coplanar waveguides to permit broadband measurements of the FMRF. As shown from measurements, the resonance can be shifted from $\text {43.2}$ GHz for the undoped sample to $\text {27.1}$ GHz and $\text{65.1}$ GHz for the films with the highest tested scandium and aluminum doping, respectively. X-ray diffraction analysis is used to evaluate the formation of secondary phases in the film. Measurement results for the hysteresis curves are obtained by vibrating sample magnetometer measurements. The results for doped and undoped samples are discussed in this letter.

Thermal-motion-induced non-reciprocal quantum optical system

Magnetic-free optical non-reciprocal components, such as isolators and circulators, are highly desirable for on-chip optical signal processing1,2 and quantum networks3,4. However, their realization presents a fundamental difficulty due to the Lorentz reciprocity in most optical devices5. In this study, we propose and experimentally realize optical non-reciprocity with atoms embedded in a ring cavity at room temperature. Random thermal motion of atoms, in the presence of a unidirectional control field, creates susceptibility–momentum locking, and subsequently a new type of chiral quantum optical system. Furthermore, we demonstrate strong non-reciprocity based on this chiral quantum system in the regime of collectively strong atom–cavity coupling. Our scheme provides a new routine towards the realization of chiral quantum optics and chip-compatible, non-magnetic optical non-reciprocity.

Magnetic-free nonreciprocal photonic platform based on time-modulated graphene capacitors

We propose a paradigm for the realization of nonreciprocal photonic devices based on time-modulated graphene capacitors coupled to photonic waveguides, without relying on magneto-optic effects. The resulting hybrid graphene-dielectric platform is low loss, silicon compatible, robust against graphene imperfections, scalable from terahertz to near-infrared frequencies, and it exhibits large nonreciprocal responses using realistic biasing schemes. We introduce an analytical framework based on solving the eigenstates of the modulated structure and on spatial coupled mode theory, unveiling the physical mechanisms that enable nonreciprocity and enabling a quick analysis and design of optimal isolator geometries based on synthetic linear and angular momentum bias. Our results, validated through harmonic-balance full-wave simulations, confirm the feasibility of the introduced low-loss ($l3$ dB) platform to realize large photonic isolation through various mechanisms, such as narrow-band asymmetric band gaps and interband photonic transitions that allow multiple isolation frequencies and large bandwidths. We envision that this technology may pave the wave to magnetic-free, fully integrated, and CMOS--compatible nonreciprocal components with wide applications in photonic networks and thermal management.

Nonreciprocity Realized with Quantum Nonlinearity.

Nonreciprocal devices are a key element for signal routing and noise isolation. Rapid development of quantum technologies has boosted the demand for a new generation of miniaturized and low-loss nonreciprocal components. Here, we use a pair of tunable superconducting artificial atoms in a 1D waveguide to experimentally realize a minimal passive nonreciprocal device. Taking advantage of the quantum nonlinear behavior of artificial atoms, we achieve nonreciprocal transmission through the waveguide in a wide range of powers. Our results are consistent with theoretical modeling showing that nonreciprocity is associated with the population of the two-qubit nonlocal entangled quasidark state, which responds asymmetrically to incident fields from opposing directions. Our experiment highlights the role of quantum correlations in enabling nonreciprocal behavior and opens a path to building passive quantum nonreciprocal devices without magnetic fields.

Ferrite loaded graphene based plasmonic waveguide

In this paper, we investigate surface plasmon (SP) propagation characteristics in a ferrite loaded graphene based waveguide biased by an external magnetic flux density. Propagation lengths and dispersion features of the excited SPs can be actively tailored via applying external electro- and magneto-static bias fields. Nonreciprocal property of the structure risen from magneto-optic behavior of the ferrite is clear, in vicinity of the Larmor frequency, according to the derived dispersion equation. The structure is investigated analytically through basic electromagnetic theory. The results can be utilized in design of nonreciprocal components.

Manipulation of the Faraday rotation by graphene metasurfaces

We demonstrate a simple structure including circular shape patterned graphene surface for manipulation of Faraday rotation phenomenon. The patterned structure can be utilized in the building blocks of vast tunable non-reciprocal components. The behavior of the structure is discussed analytically by circuit model approach and verified by numerical simulation. Obviously, manipulation of polarization rotation is attained from the circular shape pattern. Also, we show that Faraday rotation effect takes place at higher frequencies compared to the similar effect in uniform and un-patterned graphene.