Nonreciprocal Behavior Research Articles

Dynamically reconfigurable integrated optical circulators

Optical circulators that unidirectionally route light could lead to bidirectional operations in applications in data centers and telecommunications, as well as sensors. In this work, to the best of our knowledge, we present the first realization of integrated optical circulators on silicon that are electrically driven and dynamically reconfigurable. The proposed device utilizes silicon microrings with a bonded magneto-optic cladding alongside an integrated electromagnet for nonreciprocal behavior. This novel approach does not use a permanent magnet and, for this reason, it is more attractive for packaging and further integration with lasers and other photonic devices. We use this device architecture to demonstrate 4- and 6-port optical circulators with up to 14.4 dB of isolation and propose a framework to extend the design to an arbitrary number of ports. Finally, we demonstrate that it is possible to switch the electromagnet and reconfigure the circulator on a sub-nanosecond timescale, potentially adding a new level of device functionality.

Electrically Driven and Thermally Tunable Integrated Optical Isolators for Silicon Photonics

Optical isolators are required to block undesired reflections in many photonic integrated circuits (PICs), but the performance of on-chip isolators using the magneto-optic effect has been limited due to high loss of such materials. Moreover, they require precise positioning of a permanent magnet close to the chip, increasing footprint and impeding packaging. In this paper, we propose an optical isolator on the silicon-on-insulator platform with record performance and without the use of any external permanent magnets. A metallic microstrip above the bonded silicon microring (MR) is used to generate the magnetic field required for the nonreciprocal behavior. Simultaneously, the microstrip can be used to provide 0.6 nm of thermal tuning while preserving over 20 dB of isolation. We measure 32 dB of isolation near 1555 nm with only 2.3 dB excess loss in a 35 μm radius MR. The tunability, compactness, and lack of permanent magnets suggest this device is a major step towards integration in PICs.

Nonreciprocal behaviour between photon and phonon in coupled optomechanical systems

It is shown that the asymmetry coupling between two coupled optomechanical cavities leads to special class of PT-symmetric model for optomechanical structure. Under these conditions, Hamiltonian is considered in blue and red sideband regime. In these cases, the asymmetric coupling between two cavities has been transferred such that the asymmetric beam-splitter or squeezing interaction is generated between optical and mechanical modes. Then, the amount of entanglement between the different optical and mechanical modes is calculated. The results define that PT-symmetry can improve the entanglement in special conditions. The proposed system provides good condition to investigate the nonreciprocal interaction between photon and phonon.

Effect of the radial plasma nonuniformity on the propagation of guided m=+1 and m=−1 modes in helicon discharges

Theoretical as well as numerical analyses of the full set of Maxwell's equations is carried out to study non-axisymmetric (m≠ 0) guided modes in radially nonuniform helicon (HE) discharges. Unlike the axisymmetric (m = 0) modes, these modes reveal a non-reciprocal behavior with respect to the azimuthal direction. We develop the conditions for propagation and non-propagation of the various modes in the helicon parameter range, thereby focussing on the important role of the radial density gradient. Three types of modes occurring in different parameter ranges are described, i.e., the helicon (HE) mode, the electrostatic (ES) or Trivelpiece-Gould mode, and the locally coupled (LC) mode that is characterized by mode coupling (MC) in a certain region of the plasma density profile. In contrast to m=+1 modes, the parameter range of m=−1 modes is much more restricted as rather high densities are needed for the propagation of the helicon and LC modes. An important issue of the investigations is the rf power coupling and absorption via the various modes. Computations based on a simple antenna-plasma model show that the axial wavenumber of the antenna determines decisively which type of mode is excited. In case of LC mode excitation, the dominant role of the MC layer for the absorption is demonstrated. Finally, the rf power coupling to helicon modes is studied. The density limit for m=−1 helicon mode propagation and the narrow magnetic field profiles of these modes are the main reasons why the rf power absorption in helicon discharges occurs via m=+1 helicon modes.

Nonreciprocal switching in nonlinear plasmonic couplers with loss and gain

We theoretically investigate the effect of gain on switching characteristics of Kerr-nonlinear directional couplers with loss. As a model we use a coupler made of two hybrid dielectric-plasmonic slot waveguides. Introducing an asymmetric gain profile into an otherwise symmetric structure may significantly decrease the switching power and enable tuning of nonlinear characteristics. We describe evolution of the field into steady states and show that asymmetric states, which can only occur for asymmetric gain profiles, cause strongly nonreciprocal behavior of the structure.

Non-reciprocal elastic wave propagation in spatiotemporal periodic structures

We study longitudinal and transverse wave propagation in beams with elastic properties that are periodically varying in space and time. Spatiotemporal modulation of the elastic properties breaks mechanical reciprocity and induces one-way propagation. We follow an analytic approach to characterize the non-reciprocal behavior of the structures by analyzing the symmetry breaking of the dispersion spectrum, which results in the formation of directional band gaps and produces shifts of the first Brillouin zone limits. This approach allows us to relate position and width of the directional band gaps to the modulation parameters. Moreover, we identify the critical values of the modulation speed to maximize the non-reciprocal effect. We numerically verify the theoretical predictions by using a finite element model of the modulated beams to compute the transient response of the structure. We compute the two-dimensional Fourier transform of the collected displacement fields to calculate numerical band diagrams, showing excellent agreement between theoretical and numerical dispersion diagrams.

Quantum rectifier in a one-dimensional photonic channel

By using a fully quantum approach based on an input-output formulation of the stochastic Schr\"{o}dinger equation, we show rectification of radiation fields in a one-dimensional waveguide doped with a pair of ideal two-level systems for three topical cases: classical driving, under the action of noise, and single photon pulsed excitation. We show that even under the constant action of unwanted noise the device still operates effectively as an optical isolator, which is of critical importance for noise resistance. Finally, harnessing stimulated emission allows for non-reciprocal behavior for single photon inputs, thus showing purely quantum rectification at the single-photon level. The latter is a considerable step towards the ultimate goal of devising an unconditional quantum rectifier for arbitrary quantum states.

Nonreciprocal behavior of the spin pumping in ultra-thin film of CoFeB

The processional magnetization induced spin current at the interface between CoFeB and Ta has been studied experimentally using spin pumping and inverse spin Hall effect for different thicknesses of CoFeB film down to 1.6 nm. It is found that upon decreasing the thickness of the CoFeB, the frequency of the peak position of the spin pumping signal reduces and dispersion relation of the ferromagnetic resonance changes from a quadratic to a linear behavior indicating the presence of an interfacial perpendicular anisotropy. Furthermore, a nonreciprocal behavior between the spin pumping signal amplitude at positive and negative fields is observed which could be as large as 100%. Our experimental results suggest reduction of the effective demagnetization field and possibly the spin waves nonreciprocal behavior mediated by the Dzyaloshinskii-Moriya interaction at the Ta/CoFeB interface are responsible for the large nonreciprocity of the spin pumping signal.

English

Heschl’s gyrus (HG) is known to interact with other auditory related areas of the same hemisphere during the performance of an auditory cognitive task. However, the information about how it interacts with the opposite HG is still lacking. The aim of this study was to investigate the psychophysiologic interaction (PPI) between the bilateral HG during a simple arithmetic addition task and to verify the role of noise as an experimental factor that would modulate the PPI. Functional magnetic resonance imaging (fMRI) scans were performed on eighteen healthy participants, in which a single-digit addition task were solved during in-quiet (AIQ) and in-noise (AIN) conditions. The fMRI data were analysed using Statistical Parametric Mapping (SPM8). The interaction between the bilateral HG was investigated using PPI analysis. The response in right HG was found to be linearly influenced by the activity in left HG, vice-versa, for both in-quiet and in-noise conditions. The connectivity from right to left HG in noisy condition seemed to be modulated by noise, while the modulation is relatively small oppositely, indicating a non-reciprocal behavior. A two-way PPI model between right and left HG is suggested. The connectivity from right to left HG during a simple addition task in noise is driven by a higher ability of right HG to perceive the stimuli in a noisy condition. Both the bilateral HGs took part in the cognitive processes of arithmetic addition from which the interactions between the two were found to be different in noise. DOI : http://dx.doi.org/10.17576/JSKM-2016-1401-07

The luxury of igniting change by giving: Transforming yourself while transforming others' lives

This study investigates the phenomenon of luxury from a consumer perspective, by means of multisited phenomenological inquiry. The findings expand the pervasive view of luxury as accumulation of highly valued goods by offering a transformative perspective of luxury as transforming the life of distant others by giving them valuable philanthropic gifts and thereby ultimately transforming the self of the giver. The paper shows how giving away economic capital (money and time), social capital (networks and influence), and cultural capital (skills and knowledge) to non-related others can provide the giver with a sense of luxury in terms of pleasure, purpose, and connection with humankind. Thus, the findings not only extend the traditional conceptualization of luxury from having to giving, but also challenge current conceptualizations of sharing out as a non-reciprocal pro-social behavior by illustrating how ‘the luxury of giving’ relies on both pro-social and pro-ego consumption rationales, which implicitly include circular reciprocation.

Directional Phase-Matched Interaction in the Saturated Parametric Mixer

We study the nonreciprocal nature of the saturated parametric amplifier response under different pump wavelengths and power levels. The coupled-mode equations are first employed to gain more insight into the origin of directional phase-matched response. We next characterize pump depletion bandwidth and signal induced pump depletion level to identify the optimum pump wavelength and propagation direction. The nonreciprocal behavior was clearly observed at all of the examined pump wavelengths and power levels.

Optical nonreciprocity and optomechanical circulator in three-mode optomechanical systems

We demonstrate the possibility of optical nonreciprocal response in a three-mode optomechanical system where one mechanical mode is optomechanically coupled to two linearly coupled optical modes simultaneously. The optical nonreciprocal behavior is induced by the phase difference between the two optomechanical coupling rates which breaks the time-reversal symmetry of the three-mode optomechanical system. Moreover, the three-mode optomechanical system can also be used as a three-port circulator for two optical and one mechanical modes, which we refer to as optomechanical circulator.

Non-reciprocal transmission in photonic lattices based on unidirectional coherent perfect absorption.

A method for realizing asymmetric (one-way) transmission of discretized light in modulated, linear, and purely passive optical lattices is suggested, which exploits the idea of unidirectional coherent perfect absorption. The system consists of a linear photonic lattice of coupled resonators or waveguides, side coupled to a chain of lossy elements, in which light can avoid the occupation of the dissipative sites when propagating in one way, but not in the opposite one. Non-reciprocity requires modulation of the resonator/waveguide parameters, realizing a dissipative optical Aharonov-Bohm diode with non-reciprocal behavior.

Magnetically Tunable Ferrite-Loaded Half-Mode Substrate Integrated Waveguide

A magnetically tunable ferrite-loaded half-mode substrate integrated waveguide (HMSIW) is presented. To achieve the magnetic tuning, a planar Yttrium Iron Garnet (YIG) slab is loaded along the metalized wall of the HMSIW, where the concentration of the magnetic field is strongest. Static (DC) magnetic bias is applied on the ferrite slab transversely to the direction of propagation. Measured phases of forward and reverse transmission coefficients show the non-reciprocal behavior of this transmission line. Measured results illustrating the comparison between a single ferrite slab-loaded SIW and a HMSIW are presented. As an application example, a two-dimensionally tunable bandpass filter (BPF) operating at X-band is proposed and studied. By controlling the value of loaded lumped capacitors and the applied magnetic bias, a bandwidth tunable BPF is demonstrated.

Origin of Non-Reciprocal Response in Fiber Optic Parametric Amplifiers

The non-reciprocal response of high-performance fiber optic parametric amplifiers was investigated. This response is attributed to the combination of fibers' inhomogeneous nature and their operation at deep saturation, but it is not clear whether this effect is promoted by polarization or dispersion. We show that non-reciprocal behavior is dominated by the fiber's local dispersion. Additionally, a simulation strategy capable of capturing fiber optic parametric amplifiers' non-reciprocal response is demonstrated.

Optical isolator based on nonreciprocal coupling of two Tamm plasmon polaritons

In this paper, we have studied the one-dimensional photonic crystal (PC) including a magneto-optical metal defect using the developed transfer matrix method for magnetic materials. Around the two interfaces between metal and one-dimensional PC, two nonsymmetric Tamm magneto-plasmon polaritons may be excited and coupled. The coupled states take on a clear nonreciprocal behavior and result in nonreciprocal transmission. The results are demonstrated through electromagnetic field distribution simulations based on finite element software. It provides a useful reference to realize optical isolator design.

The centennial of the Sagnac experiment in the optical regime: From a tabletop experiment to the variation of the Earth's rotation

Abstract The investigation of non-reciprocal behavior of optical beams in a rotating reference frame was the main motivation of the historic tabletop experiment of George Sagnac. His ground-breaking experiment was extended to a very large installation more than a decade later, which was sensitive enough to allow Michelson, Pearson and Gale to resolve the rotation rate of the Earth by an optical interferometer. With the advent of lasers in the early sixties of the last century, rotating laser cavities with a ring structure demonstrated superior performance and very soon matured to a point where mechanical gyroscopes were quickly superseded by laser gyroscopes in aircraft navigation. When vastly upscaled ring lasers were taken back to the laboratory at the end of the 20th century, the goal of applying the Sagnac effect to geodesy for the monitoring of tiny variations of Earth's rotation was the main motivation. The large-ring laser G, which is the most stable instrument out of a series of instruments built by the New Zealand–German collaboration, routinely resolves the rotation rate of the Earth to better than eight orders of magnitude. Since G is directly referenced to the Earth rotation axis, the effect of diurnal polar motion, the Chandler and the Annual wobbles as well as tilts from the solid Earth tides can be found in the interferogram obtained from the ring laser. G has also demonstrated high sensitivity to rotations associated with seismic events. The toroidal eigenmodes of the Earth when they are excited by large earthquakes have been resolved. A surprisingly large amplitude has been measured for Love wave signals contained in the microseismic background signal. This paper summarizes the recent development of highly sensitive large Sagnac gyroscopes, and presents unique results from the measurements of rotations of the earth.

Nonreciprocity of edge modes in 1D magnonic crystal

Abstract Spin waves propagation in 1D magnonic crystals is investigated theoretically. Mathematical model based on plane wave expansion method is applied to different types of magnonic crystals, namely bi-component magnonic crystal with symmetric/asymmetric boundaries and ferromagnetic film with periodically corrugated top surface. It is shown that edge modes in magnonic crystals may exhibit nonreciprocal behaviour at much lower frequencies than in homogeneous films.

Spin wave non-reciprocity and beating in permalloy by the time-resolved magneto-optical Kerr effect

We studied the propagation characteristics of spin wave modes in a permalloy stripe by time-resolved magneto-optical Kerr effect techniques. We observed a beating interference pattern in the time domain under the influence of an electrical square pulse excitation at the centre of the stripe. We also probed the non-reciprocal behaviour of propagating spin waves with a dependence on the external magnetic field. Spatial dependence studies showed that localized edge mode spin waves have a lower frequency than the spin waves at the centre of the stripe, due to the varying magnetization vector across the width of the stripe.

Nonreciprocal transmission through a saturable nonlinear asymmetric dimer.

We investigate the nonreciprocal diodelike behavior of a dimer with an asymmetric on-site potential and a saturable nonlinearity. The dimer is coupled to linear side chains. The spectra of transmission and the rectifying factor are analytically obtained using a backward iteration of the set of discrete nonlinear Schrödinger equations used to model the wave propagation through the nonlinear dimer. We show that the windows of bistable behavior leading to a pronounced nonreciprocal diodelike transmission become wider and displaced to higher input field intensities as the saturation coefficient increases. Further, saturation of the nonlinear response has opposite impacts on the rectifying action over short- and long-wavelength input signals within the second bistability window. In the first window, the rectifying action is not compromised by the saturation, thus showing that a weak contribution of high-order susceptibilities to the nonlinear response can improve the efficiency of the nonreciprocal transmission. The rectifying action of a dimer with an asymmetric nonlinearity is also discussed.