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In the multi-load wireless power transfer (WPT) system, the output power and transfer efficiency will drop significantly with the change of distance between transmitter and receiver. Power distribution among multiple loads is also a major challenge. In order to solve these problems, a novel multi-load WPT system based on parity–time symmetry (PT-WPT) is proposed in this paper. Firstly, the multi-load PT-WPT system is modeled based on the circuit model. Then, the transmission characteristics of the multi-load PT-WPT system are analyzed. It is found that constant output power with constant transfer efficiency can be maintained against the variation of coupling coefficient, and the power distribution relationship among loads is only related to the coupling coefficient. Further, power distribution under different coupling situations is analyzed in detail to meet different power demands. Finally, taking a dual-load PT-WPT system as an example, the system parameters are designed and the circuit simulation is carried out. The simulation results are consistent with the theoretical analysis, which shows that PT symmetry can be applied to the multi-load WPT system to achieve constant output power, constant transfer efficiency, and power distribution simultaneously.

We theoretically and numerically demonstrate that the spontaneous parity-time (PT) symmetry breaking phase transition can be realized respectively by using two independent tuning ways in a tri-layered metamaterial that consists of periodic array of metal-semiconductor Schottky junctions. The existence conditions of PT symmetry and its phase transition are obtained by using a theoretical model based on the coupled mode theory. A hot-electron photodetection based on the same tri-layered metamaterial is proposed, which can directly show the spontaneous PT symmetry breaking phase transition in photocurrent and possesses dynamical tunability and switchability. This work extends the concept of PT symmetry into the hot-electron photodetection, enriches the functionality of the metamaterial and the hot-electron device, and has varieties of potential and important applications in optoelectronics, photodetection, photovoltaics, and photocatalytics.

Effect of optical loss, presented in a superstructure grating with a complex refractive index profile, on the mode coupling is studied in a two-mode silicon-on-insulator waveguide. In this scheme, both our theory and experimental results indicate that the optical loss not only provides optical absorption of a targeted output mode and thus the corresponding modal coupling loss, but also induces a broken parity-time symmetry phase that strongly prohibits power coupling from the incident mode to the output mode. As a result, the latter can give rise to a much-enhanced modal coupling loss of the targeted output mode. Under a reasonable device length about 37 μm, the enhancement factor can be as high as ~20 dB in simulation and ~17 dB in experiment. This paper may offer a different way to exploit the role of optical loss in boosting modal coupling loss that can directly translate to power extinction ratio. It thus may find potential applications in novel intensity modulator designs.

We report on the lasing action in weakly modulated parity-time (PT) symmetric lattices. At the exceptional point in PT-symmetric lattices, the amplitude and phase of unidirectionally scattered waves are independently and flexibly determined by the PT modulations, thus, providing a distinctive route to construct a lasing mode in finite systems with weakly modulated structures. It is revealed that the resonant feedback mechanism plays a crucial role in building up the lasing action. Our finding would enrich the singularity dynamics in the weakly modulated PT systems.

Defect modes of defective parity-time symmetry in one-dimensional fractional Schrödinger equation are theoretically investigated. Both positive and negative defect modes are extremely sensitive to the defect strength and amplitude of periodic potential. Their eigenvalues increase almost linearly with the defect strength and continuously jump among neighboring gaps in the entire defect strength domain. There exists a phase transition point where two adjacent defect mode curves merge into a single one. Below which the eigenvalues are real, and their profiles have the same symmetry as the parity-time symmetric potential. Above the transition point, the defect modes give rise to complex eigenvalues, and the above symmetric property is destroyed. The transition point also grows linearly with the defect strength. As defect strength increases, much more positive defect mode branches merge together and more phase transition points appear in each gap. However, only one phase transition point exists for negative defect modes, and moves into the higher gaps.

In standard quantum theory, the Hamiltonian describing a physical system is assumed to be Hermitian in order to guarantee the energy spectrum to be real and the time evolution to be unitary. In recent years, it was recognized that non-Hermitian Hamiltonians with parity-time ($ \mathcal PT $) symmetry can exhibit entirely real spectra, raising the possibility for extending the quantum theory to complex domain and hence stimulated growing interest in recent years. Many proposals have been presented for realizing $ \mathcal PT $-symmetric Hamiltonians in various physical systems. Among them $ \mathcal PT $-symmetric coherent atomic gases are special and possess many unique advantages, including the possibility to obtain authentic $ \mathcal PT $-symmetric refractive indexes (which have balanced gain and loss in the whole space), the capability to actively control and precisely manipulate system parameters in situ, and the feasibility to acquire large Kerr nonlinearity based on the resonance character between light and atoms. In this article, we review various schemes for the realization of $ \mathcal PT $ symmetry with coherent atomic gases, elucidate their interesting properties and promising applications. In particular, the non-linear optical effect in the $ \mathcal PT $-symmetric atomic gases are described, which may be served as useful building blocks for developing novel photonic devices with active light control at very low power level.

In this article, we study the interactions of electromagnetic waves with a non-dispersive dynamic medium that is temporally dependent. Electromagnetic fields under material time-modulation conserve their momentum but not their energy. We assume a time-variation of permittivity, permeability, and conductivity, and derive the appropriate time-domain solutions based on the causality state at a past observation time. We formulate a time-transitioning state matrix and connect the unusual energy transitions of electromagnetic fields in time-varying media with the exceptional point theory. This state-matrix approach allows us to analyze further the electromagnetic waves in terms of parity and time-reversal symmetries and signify parity-time symmetric wave-states without the presence of a spatially symmetric distribution of gain and loss, or any inhomogeneities and material periodicity. This article provides a useful arsenal to study electromagnetic wave phenomena under time-varying media and points out novel physical insights connecting the resulting energy transitions and electromagnetic modes with exceptional point physics and operator symmetries.

To achieve ultrafast neuromorphic signal processing, the realization of photonic equivalents to neuronal functions has been challenged. In article number 1900771, Namkyoo Park and co‐workers present a neuromorphic photonic system ruled by parity‐time symmetry as a building block for light‐based neural signal processing. Inspired by neuronal ion channels, saturable photonic channels using coupled resonators are developed to achieve multifaceted neuromorphic functionalities such as quenching and firing.

International audience; The impact of imbalance in waveguides propagation constants among Parity-Time symmetric coupled waveguides and/or of a complex-valued coupling coefficient is assessed. The narrow tolerance found implies that attempts to tightly control waveguides parameters appear as elusive because of fabrication technology limitations, calling for more feasible mitigation avenues. It is shown that a grating-assisted Parity-Time symmetric coupler design restores both technologically robust binary switching operation and exceptional point. In addition the proposed design is compatible with birefringence compensation techniques providing polarization-independent operation as well as coupling and/or gain-loss profile modulation techniques that extend the control of switching operation in the Parity-Time symmetric phase. Using wavelength as an additional tuning parameter near exceptional points opens promising avenues for manipulating the trajectory on Riemann sheets in topological photonics applications.

We report on the numerical analysis of intensity dynamics of a pair of mutually coupled, single-mode semiconductor lasers that are operated in a configuration that leads to features reminiscent of parity&ndash, time symmetry. Starting from the rate equations for the intracavity electric fields of the two lasers and the rate equations for carrier inversions, we show how these equations reduce to a simple 2 &times, 2 effective Hamiltonian that is identical to that of a typical parity&ndash, time (PT)-symmetric dimer. After establishing that a pair of coupled semiconductor lasers could be PT-symmetric, we solve the full set of rate equations and show that despite complicating factors like gain saturation and nonlinearities, the rate equation model predicts intensity dynamics that are akin to those in a PT-symmetric system. The article describes some of the advantages of using semiconductor lasers to realize a PT-symmetric system and concludes with some possible directions for future work on this system.

For a given operator D ( t ) of an observable in theoretical parity-time symmetric quantum physics (or for its evolution-generator analogues in the experimental gain-loss classical optics, etc.) the instant t c r i t i c a l of a spontaneous breakdown of the parity-time alias gain-loss symmetry should be given, in the rigorous language of mathematics, the Kato’s name of an “exceptional point”, t c r i t i c a l = t ( E P ) . In the majority of conventional applications the exceptional point (EP) values are not real. In our paper, we pay attention to several exactly tractable toy-model evolutions for which at least some of the values of t ( E P ) become real. These values are interpreted as “instants of a catastrophe”, be it classical or quantum. In the classical optical setting the discrete nature of our toy models might make them amenable to simulations. In the latter context the instant of Big Bang is mentioned as an illustrative sample of possible physical meaning of such an EP catastrophe in quantum cosmology.

We considered the modulational instability of continuous-wave backgrounds, and the related generation and evolution of deterministic rogue waves in the recently introduced parity–time (PT )-symmetric system of linearly coupled nonlinear Schr¨ odinger equations, which describes a Kerr-nonlinear optical coupler with mutually balanced gain and loss in its cores. Besides the linear coupling, the overlapping cores are coupled through the cross-phase-modulation term too. While the rogue waves, built according to the pattern of the Peregrine soliton, are (quite naturally) unstable, we demonstrate that the focusing cross-phase-modulation interaction results in their partial stabilization. For PT -symmetric and antisymmetric bright solitons, the stability region is found too, in an exact analytical form, and verified by means of direct simulations., Fundação para a Ciência e a Tecnologia (FCT), Binational (US–Israel) Science Foundation.