A widely-wavelength-tunable Brillouin fiber laser(BFL)with improved optical signal-to-noise ratio(OSNR)based on parity-time(PT)symmetric and saturable absorption(SA)effect is present.This novel BFL realizes PT symmetr...A widely-wavelength-tunable Brillouin fiber laser(BFL)with improved optical signal-to-noise ratio(OSNR)based on parity-time(PT)symmetric and saturable absorption(SA)effect is present.This novel BFL realizes PT symmetry and SA effect through polarization-maintaining erbium-doped fiber(PM-EDF)Sagnac loop,which is composed of a PM-EDF,a coupler and two polarization controllers(PCs).By using the inherent birefringence characteristic of PM-EDF,two feedback loops in orthogonal polarization state are formed when the Strokes signal in injected.One of these loops provides gain in the clockwise direction with in the Sagnac loop,while the other loop generates loss in the counterclockwise direction.By adjusting the PCs to control the polarization state of the PM-EDF,a single-longitudinal-mode(SLM)BFL can be achieved,as the PT symmetry is broken when the SA participating stimulated Brillouin scattering(SBS)gain and loss are well-matched and the gain surpasses the coupling coefficient.Compared to previous BFLs,the proposed BFL has a more streamlined structure and a wider wavelength tunable range,at the same time,it is not being limited by the bandwidth of the erbium-doped fiber amplifier while still maintaining narrow linewidth SLM output.Additionally,thanks to SA effect of the PM-EDF,the PT symmetric SBS gain contract is enhanced,resulting in a higher optical signal-to-noise(OSNR).The experimental results show that the laser has a wide tunable range of 1526.088 nm to 1565.498 nm,an improved OSNR of 77 dB,and a fine linewidth as small as 140.5 Hz.展开更多
Phase transition from the over-damping to under-damping states is a ubiquitous phenomenon in physical systems. However, what kind of symmetry is broken associated with this phase transition remains unclear. Here, we d...Phase transition from the over-damping to under-damping states is a ubiquitous phenomenon in physical systems. However, what kind of symmetry is broken associated with this phase transition remains unclear. Here, we discover that this phase transition is determined by an anti-parity-time(anti-PT) symmetry hidden in a single damping linear resonator, which is significantly different from the conventional anti-PT-symmetric systems with two or more modes. We show that the breaking of the anti-PT symmetry yields the phase transition from the over-damping to under-damping states, with an exceptional point(EP) corresponding to the critical-damping state. Moreover, we propose an optomechanical scheme to show this anti-PT symmetry breaking by using the optical spring effect in a quadratic optomechanical system. We also suggest an optomechanical sensor with the sensitivity enhanced significantly around the EPs for the anti-PT symmetry breaking. Our work unveils the anti-PT symmetry hidden in damping oscillations and hence opens up new possibilities for exploiting wide anti-PT symmetry applications in single damping linear resonators.展开更多
A model of the photonic spin Hall effect(PSHE)in antisymmetric parity-time(APT)metamaterials with incidence of Gaussian beams is proposed here.We derive the displacement expression of the PSHE in APT metamaterials bas...A model of the photonic spin Hall effect(PSHE)in antisymmetric parity-time(APT)metamaterials with incidence of Gaussian beams is proposed here.We derive the displacement expression of the PSHE in APT metamaterials based on the transport properties of Gaussian beams in positive and negative refractive index materials.Furthermore,detailed discussions are provided on the APT scattering matrix,eigenstate ratio,and response near exceptional points in the case of loss or gain.In contrast to the unidirectional non-reflection in parity-time(PT)symmetric systems,the transverse shift that arises from both sides of the APT structure is consistent.By effectively adjusting the parameters of APT materials,we achieve giant displacements of the transverse shift.Finally,we present a multi-layer APT structure consisting of alternating left-handed and right-handed materials.By increasing the number of layers,Bragg oscillations can be generated,leading to an increase in resonant peaks in transverse shift.This study presents a new approach to achieving giant transverse shifts in the APT structure.This lays a theoretical foundation for the fabrication of related nano-optical devices.展开更多
Non-Hermitian systems featuring exceptional points(EPs)or spectral coalescences of eigenvalues and eigenfunctions have led to many surprisingly important applications, such as single-mode lasing, loss-induced transpar...Non-Hermitian systems featuring exceptional points(EPs)or spectral coalescences of eigenvalues and eigenfunctions have led to many surprisingly important applications, such as single-mode lasing, loss-induced transparency, and highprecision metrology. However, most previous demonstrations of EPs have necessitated at least two coupled modes,thereby limiting the achievement and utilization of EPs in a wide range of single-mode systems.展开更多
This work studies the dynamical transmission of chirped optical solitons in a spatially inhomogeneous nonlinear fiber with cubic-quintic-septic nonlinearity,weak nonlocal nonlinearity,self-frequency shift and parity-t...This work studies the dynamical transmission of chirped optical solitons in a spatially inhomogeneous nonlinear fiber with cubic-quintic-septic nonlinearity,weak nonlocal nonlinearity,self-frequency shift and parity-time(PT)symmetry potential.A generalized variable-coefficient nonlinear Schr?dinger equation that models the dynamical evolution of solitons has been investigated by the analytical method of similarity transformation and the numerical mixed method of split-step Fourier method and Runge–Kutta method.The analytical self-similar bright and kink solitons,as well as their associated frequency chirps,are derived for the first time.We found that the amplitude of the bright and kink solitons can be controlled by adjusting the imaginary part of the PT-symmetric potential.Moreover,the influence of the initial chirp parameter on the soliton pulse widths is quantitatively analyzed.It is worth emphasizing that we could control the chirp whether it is linear or nonlinear by adjusting optical fiber parameters.The simulation results of bright and kink solitons fit perfectly with the analytical ones,and the stabilities of these soliton solutions against noises are checked by numerical simulation.展开更多
Traditional light sources cannot emit an electromagnetic(EM)field with an orbital angular momentum(OAM),limiting their applications in modern optics.The recent development of the OAM laser,mainly based on micro-and na...Traditional light sources cannot emit an electromagnetic(EM)field with an orbital angular momentum(OAM),limiting their applications in modern optics.The recent development of the OAM laser,mainly based on micro-and nanostructures,can satisfy the increasing requirements for on-chip photonics and information capacities.Nevertheless,the photonic structures have fixed parameters that prevent these OAM lasers from being dynamically tuned.Here,we propose tunable vortex lasing from a microring cavity integrated by a phase change material,Ge_(2)Sb_(2)Te_(5)(GST225).By modulating the complex refractive index to create an exceptional point(EP)to break the degeneracy of whispering gallery modes with opposite orientations,the microlaser working at the EP can impart an artificial angular momentum,thus emitting vortex beams with well-defined OAM.The grating scatter on the edge of the microring can provide efficient vertical radiation.The vortex laser wavelength from the GST225/InGaAsP dual-layered microring cavity can be dynamically tuned by switching the state of GST225 between amorphous and crystalline without changing the microring geometry.We construct an electric-thermal model to show the tuning range of operating wavelengths(EPs)from 1544.5 to 1565.9 nm in~25 ns.Our study on high-speed tunable PT-symmetry vortex lasers facilitates the next generation of integrated optoelectronic devices for optical computing and communications in both classical and quantum regions.展开更多
In order to realize the ultrastrong absorption of graphene with electrical modulation properties, we designed a composite structure of graphene and parity-time(PT) symmetry photonic crystal, which is achieved by placi...In order to realize the ultrastrong absorption of graphene with electrical modulation properties, we designed a composite structure of graphene and parity-time(PT) symmetry photonic crystal, which is achieved by placing the graphene layer on the top layer of the PT symmetry photonic crystal. In this paper, the absorption properties of graphene and the electrical modulating properties of the structure were theoretically analyzed based on the transfer matrix method. The result shows that the proposed structure can achieve the absorption of 31.5 d B for the communication wavelength of 1550 nm;meanwhile,by setting the electric field intensity to ±0.02 V/nm, the absorption of graphene can be largely modulated to realize an electrically switchable effect, the modulation depth of graphene absorption can reach nearly 100%, and the operation speed is also close to 8.171 GHz. This investigation provides a novel approach to design graphene-based optoelectronic devices and optical communication devices.展开更多
The dynamics of spin–orbit-coupled Bose–Einstein condensate with parity-time symmetry through a moving obstacle potential is simulated numerically. In the miscible two-component condensate, the formation of the K...The dynamics of spin–orbit-coupled Bose–Einstein condensate with parity-time symmetry through a moving obstacle potential is simulated numerically. In the miscible two-component condensate, the formation of the Kármán vortex street is observed in one component, while ‘the half-quantum vortex street' is observed in the other component. Other patterns of vortex shedding, such as oblique vortex dipoles, V-shaped vortex pairs, irregular turbulence, and combined modes of various wakes, can also be found. The ratio of inter-vortex spacing in one row to the distance between vortex rows is approximately0.18, which is less than the stability condition 0.28 of classical fluid. The drag force acting on the obstacle potential is simulated. The parametric regions of Kármán vortex street and other vortex patterns are calculated. The range of Kármán vortex street is surrounded by the region of combined modes. In addition, spin–orbit coupling disrupts the symmetry of the system and the gain-loss affects the local particle distribution of the system, which leads to the local symmetry breaking of the system, and finally influences the stability of the Kármán vortex street. Finally, we propose an experimental protocol to realize the Kármán vortex street in a system.展开更多
Since the first observation of parity-time（PT） symmetry in optics, varied interesting phenomena have been discovered in both theories and experiments, such as PT phase transition and unidirectional invisibility, whi...Since the first observation of parity-time（PT） symmetry in optics, varied interesting phenomena have been discovered in both theories and experiments, such as PT phase transition and unidirectional invisibility, which turns PT-symmetric optics into a hotspot in research. Here, we report on the one-way localized Fabry-Pérot（FP） resonance, where a welldesigned PT optical resonator may operate at exceptional points with bidirectional transparency but unidirectional field localization. Overtones of such one-way localized FP resonance can be classified into a blue shifted branch and a red shifted branch. Therefore, the fundamental resonant frequency is not the lowest one. We find that the spatial field distributions of the overtones at the same absolute order are almost the same, even though their frequencies are quite different.展开更多
Researches on parity-time(PT)symmetry in acoustic field can provide an efficient platform for controlling the travelling acoustic waves with balanced loss and gain.Here,we report a feasible design of PT-symmetric syst...Researches on parity-time(PT)symmetry in acoustic field can provide an efficient platform for controlling the travelling acoustic waves with balanced loss and gain.Here,we report a feasible design of PT-symmetric system constructed by piezoelectric composite plates with two different active external circuits.By judiciously adjusting the resistances and inductances in the external circuits,we obtain the exceptional point due to the spontaneous breaking of PT symmetry at the desired frequencies and can observe the unidirectional invisibility.Moreover,the system can be at PT exact phase or broken phase at the same frequency in the same structure by merely adjusting the external circuits,which represents the active control that makes the acoustic manipulation more convenient.Our study may provide a feasible way for manipulating acoustic waves and inspire the application of piezoelectric composite materials in acoustic structures.展开更多
In this paper, the （l＋l）-dimensional variable-coefficient complex Ginzburg-Landau （CGL） equation with a parity- time （PT） symmetric potential U（x） is investigated. Although the CGL equations with a PT-symmetr...In this paper, the （l＋l）-dimensional variable-coefficient complex Ginzburg-Landau （CGL） equation with a parity- time （PT） symmetric potential U（x） is investigated. Although the CGL equations with a PT-symmetric potential are less reported analytically, the analytic solutions for the CGL equation are obtained with the bilinear method in this paper. Via the derived solutions, some soliton structures are presented with corresponding parameters, and the influences of them are analyzed and studied. The single-soliton structure is numerically verified, and its stability is analyzed against additive and multiplicative noises. In particular, we study the soliton dynamics under the impact of the PT-symmetric potential. Results show that the PT-symmetric potential plays an important role for obtaining soliton structures in ultrafast optics, and we can design fiber lasers and all-optical switches depending on the different amplitudes of soliton-like structures.展开更多
We experimentally simulate a parity-time(PT)-symmetric quantum dynamics in a non-Hermitian system using a single-photon interferometer.We measure quantum final state using quantum state tomography.We observe the quant...We experimentally simulate a parity-time(PT)-symmetric quantum dynamics in a non-Hermitian system using a single-photon interferometer.We measure quantum final state using quantum state tomography.We observe the quantum state evolutions ranging from regions of unbroken to broken PT-symmetry using the single-photon interferometer.We experimentally prove that the eigenvalue of energy changes from real to imaginary corresponding to the non-Hermitian system from the PT-symmetry unbroken region to the PT-symmetry broken region.To the best of our knowledge,this is the first work to intuitively show the exceptional points of PT-symmetry non-unitary quantum dynamics in a single-photon interferometer from the energy perspective.展开更多
We experimentally investigate the impact of static disorder and dynamic disorder on the non-unitary dynamics of parity-time(PT)-symmetric quantum walks.Via temporally alternating photon losses in an interferometric ne...We experimentally investigate the impact of static disorder and dynamic disorder on the non-unitary dynamics of parity-time(PT)-symmetric quantum walks.Via temporally alternating photon losses in an interferometric network,we realize the passive PT-symmetric quantum dynamics for single photons.Controllable coin operations allow us to simulate different environmental influences,which result in three different behaviors of quantum walkers:a standard ballistic spread,a diffusive behavior,and a localization,respectively,in a PT-symmetric quantum walk architecture.展开更多
Parity-time (PT) symmetry/anti-parity-time (APT) symmetry in non-Hermitian systems reveal profound physics andspawn intriguing effects. Recently, it has been introduced into diffusive systems together with the concept...Parity-time (PT) symmetry/anti-parity-time (APT) symmetry in non-Hermitian systems reveal profound physics andspawn intriguing effects. Recently, it has been introduced into diffusive systems together with the concept of exceptionalpoints (EPs) from quantum mechanics and the wave systems. With the aid of convection, we can generate complex thermalconductivity and imitate various wavelike dynamics in heat transfer, where heat flow can be “stopped” or moving against thebackground motion. Non-Hermitian diffusive systems offer us a new platform to investigate the heat wave manipulation.In this review, we first introduce the construction of APT symmetry in a simple double-channel toy model. Then we showthe phase transition around the EP. Finally, we extend the double-channel model to the four-channel one for showing thehigh-order EP and the associated phase transition. In a general conclusion, the phase difference of adjacent channels isalways static in the APT symmetric phase, while it dynamically evolves or oscillates when the APT symmetry is broken.展开更多
Symmetry plays a crucial role in explorations of the laws of nature.Parity-time(PT)symmetry phenomena can lead to entirely real spectra in non-Hermitian systems,which attracts considerable attention in the fields of o...Symmetry plays a crucial role in explorations of the laws of nature.Parity-time(PT)symmetry phenomena can lead to entirely real spectra in non-Hermitian systems,which attracts considerable attention in the fields of optics and electronics because these phenomena provide a new tool for the manipulation of oscillation modes and nonreciprocal signal transmission.A potential new field of application is microwave photonics,an interdisciplinary field in which the interaction between microwaves and optical signals is exploited.In this article,we report the experimental use of PT symmetry in an optoelectronic oscillator(OEO),a key microwave photonics system that can generate singlefrequency sinusoidal signals with high spectral purity.PT symmetry is theoretically analyzed and experimentally observed in an OEO with two mutually coupled active oscillation cavities via a precise manipulation of the interplay between gain and loss in the two oscillation cavities.Stable single-frequency microwave oscillation is achieved without using any optical/electrical filters for oscillation mode selection,which is an indispensable requirement in traditional OEOs.This observation opens new avenues for signal generation and processing based on the PT symmetry principle in microwave photonics.展开更多
In recent years,parity-time(PT)symmetry in optoelectronic systems has been widely studied,due to its potential applications in lasers,sensors,topological networks,and other fields.In this paper,a time-division multipl...In recent years,parity-time(PT)symmetry in optoelectronic systems has been widely studied,due to its potential applications in lasers,sensors,topological networks,and other fields.In this paper,a time-division multiplexed pulsed optoelectronic oscillator(OEO)is proposed to study the dynamics of a PT symmetry system.Two microwave pulses are used to realize the PT symmetry in a single spatial resonator based on the temporal degrees of freedom.The gain and loss of the microwave pulses and the coupling coefficient between them can then be controlled.We first demonstrate the phase diagram from PT broken to PT symmetry in the OEO system.We theoretically prove that the perturbation of a coupling-induced phase shift larger than(2π)×10^(-2)causes the disappearance of the PT symmetry.In this experiment,the perturbation is less than(2π)×0.5×10^(-2);thus,the phase transition of PT symmetry is observed.In addition,multipairs of PT-symmetry pulses indicate that pulsed OEO could be used to implement complex non-Hermitian Hamilton systems.Therefore,it is confirmed that pulsed OEO is an excellent platform to explore the dynamics of PT symmetry and other non-Hermitian Hamiltonian systems.展开更多
Parity-time(PT)symmetry has attracted intensive research interest in recent years.PT symmetry is conventionally implemented between two spatially distributed subspaces with identical localized eigenfrequencies and com...Parity-time(PT)symmetry has attracted intensive research interest in recent years.PT symmetry is conventionally implemented between two spatially distributed subspaces with identical localized eigenfrequencies and complementary gain and loss coefficients.The implementation is complicated.In this paper,we propose and demonstrate that PT symmetry can be implemented between two subspaces in a single spatial unit based on optical polarimetric diversity.By controlling the polarization states of light in the single spatial unit,the localized eigenfrequencies,gain,loss,and coupling coefficients of two polarimetric loops can be tuned,leading to PT symmetry breaking.As a demonstration,a fiber ring laser based on this concept supporting stable and single-mode lasing without using an ultranarrow bandpass filter is implemented.展开更多
Encircling an exceptional point(EP) in a parity-time(PT) symmetric system has shown great potential for chiral optical devices,such as chiral mode switching for symmetric and antisymmetric modes.However,to our best kn...Encircling an exceptional point(EP) in a parity-time(PT) symmetric system has shown great potential for chiral optical devices,such as chiral mode switching for symmetric and antisymmetric modes.However,to our best knowledge,chiral switching for polarization states has never been reported,although chiral polarization manipulation has significant applications in imaging,sensing,communication,etc.Here,inspired by the anti-PT symmetry,we demonstrate,for the first time to our best knowledge,an on-chip chiral polarizer by constructing a polarization-coupled anti-PT symmetric system.The transmission axes of the chiral polarizer are different for forward and backward propagation.A polarization extinction ratio of over 10 dB is achieved for both propagating directions.Moreover,a telecommunication experiment is performed to demonstrate the potential applications in polarization encoding signals.It provides a novel functionality for encircling-an-EP parametric evolution and offers a new approach for on-chip chiral polarization manipulation.展开更多
This paper studies two-lane asymmetric simple exclusion processes(ASEPs)with an intersection.In the upstream segments of the intersection,one particle can move to the next site with rate 1 if the site is empty,and the...This paper studies two-lane asymmetric simple exclusion processes(ASEPs)with an intersection.In the upstream segments of the intersection,one particle can move to the next site with rate 1 if the site is empty,and the other particle can move forward with rate p in the sites of downstream segments.The parameter p can represent the rate of slowing of motion,and the parameter is introduced to investigate spontaneous symmetry breaking(SSB)phenomenon.Extensive Monte Carlo simulations are carried out.It is shown that three symmetric phases exist and the SSB does not exist in the system.Simple mean field approach in which correlation of sites is ignored is firstly adopted to analyze the system,and the system is divided into four independent segments.It is found that the analytical results deviate from the simulation ones,especially when p is small.In addition,the inexsitence of SSB can only be explained qualitatively.Motivated by this,we carry out the cluster mean field analysis in which correlation of five sites is considered.It is shown that densities of the two upstream segments are equal,which demonstrates that the SSB does not exist.It is also shown that,as expected,the cluster mean field analysis performs much better than the simple mean field analysis.展开更多
The conditions for the emergence of the non-Hermitian skin effect, as a unique physical response of non-Hermitian systems, have now become one of the hot research topics. In this paper, we study the novel physical res...The conditions for the emergence of the non-Hermitian skin effect, as a unique physical response of non-Hermitian systems, have now become one of the hot research topics. In this paper, we study the novel physical responses of nonHermitian systems with anomalous time-reversal symmetry, in both one dimension and two dimensions. Specifically, we focus on whether the systems will exhibit a non-Hermitian skin effect. We employ the theory of generalized Brillouin zone and also numerical methods to show that the anomalous time-reversal symmetry can prevent the skin effect in onedimensional non-Hermitian systems, but is unable to exert the same effectiveness in two-dimensional cases.展开更多
文摘A widely-wavelength-tunable Brillouin fiber laser(BFL)with improved optical signal-to-noise ratio(OSNR)based on parity-time(PT)symmetric and saturable absorption(SA)effect is present.This novel BFL realizes PT symmetry and SA effect through polarization-maintaining erbium-doped fiber(PM-EDF)Sagnac loop,which is composed of a PM-EDF,a coupler and two polarization controllers(PCs).By using the inherent birefringence characteristic of PM-EDF,two feedback loops in orthogonal polarization state are formed when the Strokes signal in injected.One of these loops provides gain in the clockwise direction with in the Sagnac loop,while the other loop generates loss in the counterclockwise direction.By adjusting the PCs to control the polarization state of the PM-EDF,a single-longitudinal-mode(SLM)BFL can be achieved,as the PT symmetry is broken when the SA participating stimulated Brillouin scattering(SBS)gain and loss are well-matched and the gain surpasses the coupling coefficient.Compared to previous BFLs,the proposed BFL has a more streamlined structure and a wider wavelength tunable range,at the same time,it is not being limited by the bandwidth of the erbium-doped fiber amplifier while still maintaining narrow linewidth SLM output.Additionally,thanks to SA effect of the PM-EDF,the PT symmetric SBS gain contract is enhanced,resulting in a higher optical signal-to-noise(OSNR).The experimental results show that the laser has a wide tunable range of 1526.088 nm to 1565.498 nm,an improved OSNR of 77 dB,and a fine linewidth as small as 140.5 Hz.
基金supported by the National Natural Science Foundation of China(Grant Nos.12064010,12247105,12175061,11935006,11774086,1217050862,and 11775075)the Natural Science Foundation of Hunan Province(Grant No.2021JJ20036)the Science and Technology Innovation Program of Hunan Province(Grant Nos.2022RC1203,2020RC4047,and 2021RC4029)。
文摘Phase transition from the over-damping to under-damping states is a ubiquitous phenomenon in physical systems. However, what kind of symmetry is broken associated with this phase transition remains unclear. Here, we discover that this phase transition is determined by an anti-parity-time(anti-PT) symmetry hidden in a single damping linear resonator, which is significantly different from the conventional anti-PT-symmetric systems with two or more modes. We show that the breaking of the anti-PT symmetry yields the phase transition from the over-damping to under-damping states, with an exceptional point(EP) corresponding to the critical-damping state. Moreover, we propose an optomechanical scheme to show this anti-PT symmetry breaking by using the optical spring effect in a quadratic optomechanical system. We also suggest an optomechanical sensor with the sensitivity enhanced significantly around the EPs for the anti-PT symmetry breaking. Our work unveils the anti-PT symmetry hidden in damping oscillations and hence opens up new possibilities for exploiting wide anti-PT symmetry applications in single damping linear resonators.
基金the Natural Science Foundation of Guangdong Province(Grant Nos.2018A030313480 and 2022A1515012377)。
文摘A model of the photonic spin Hall effect(PSHE)in antisymmetric parity-time(APT)metamaterials with incidence of Gaussian beams is proposed here.We derive the displacement expression of the PSHE in APT metamaterials based on the transport properties of Gaussian beams in positive and negative refractive index materials.Furthermore,detailed discussions are provided on the APT scattering matrix,eigenstate ratio,and response near exceptional points in the case of loss or gain.In contrast to the unidirectional non-reflection in parity-time(PT)symmetric systems,the transverse shift that arises from both sides of the APT structure is consistent.By effectively adjusting the parameters of APT materials,we achieve giant displacements of the transverse shift.Finally,we present a multi-layer APT structure consisting of alternating left-handed and right-handed materials.By increasing the number of layers,Bragg oscillations can be generated,leading to an increase in resonant peaks in transverse shift.This study presents a new approach to achieving giant transverse shifts in the APT structure.This lays a theoretical foundation for the fabrication of related nano-optical devices.
文摘Non-Hermitian systems featuring exceptional points(EPs)or spectral coalescences of eigenvalues and eigenfunctions have led to many surprisingly important applications, such as single-mode lasing, loss-induced transparency, and highprecision metrology. However, most previous demonstrations of EPs have necessitated at least two coupled modes,thereby limiting the achievement and utilization of EPs in a wide range of single-mode systems.
基金the National Natural Science Foundation of China(Grant No.11975172)
文摘This work studies the dynamical transmission of chirped optical solitons in a spatially inhomogeneous nonlinear fiber with cubic-quintic-septic nonlinearity,weak nonlocal nonlinearity,self-frequency shift and parity-time(PT)symmetry potential.A generalized variable-coefficient nonlinear Schr?dinger equation that models the dynamical evolution of solitons has been investigated by the analytical method of similarity transformation and the numerical mixed method of split-step Fourier method and Runge–Kutta method.The analytical self-similar bright and kink solitons,as well as their associated frequency chirps,are derived for the first time.We found that the amplitude of the bright and kink solitons can be controlled by adjusting the imaginary part of the PT-symmetric potential.Moreover,the influence of the initial chirp parameter on the soliton pulse widths is quantitatively analyzed.It is worth emphasizing that we could control the chirp whether it is linear or nonlinear by adjusting optical fiber parameters.The simulation results of bright and kink solitons fit perfectly with the analytical ones,and the stabilities of these soliton solutions against noises are checked by numerical simulation.
基金The National Key Research and Development Program of China(2019YFA0709100.2020YFA0714504)the program of the National Natural Science Foundation of China(No.62105054)。
文摘Traditional light sources cannot emit an electromagnetic(EM)field with an orbital angular momentum(OAM),limiting their applications in modern optics.The recent development of the OAM laser,mainly based on micro-and nanostructures,can satisfy the increasing requirements for on-chip photonics and information capacities.Nevertheless,the photonic structures have fixed parameters that prevent these OAM lasers from being dynamically tuned.Here,we propose tunable vortex lasing from a microring cavity integrated by a phase change material,Ge_(2)Sb_(2)Te_(5)(GST225).By modulating the complex refractive index to create an exceptional point(EP)to break the degeneracy of whispering gallery modes with opposite orientations,the microlaser working at the EP can impart an artificial angular momentum,thus emitting vortex beams with well-defined OAM.The grating scatter on the edge of the microring can provide efficient vertical radiation.The vortex laser wavelength from the GST225/InGaAsP dual-layered microring cavity can be dynamically tuned by switching the state of GST225 between amorphous and crystalline without changing the microring geometry.We construct an electric-thermal model to show the tuning range of operating wavelengths(EPs)from 1544.5 to 1565.9 nm in~25 ns.Our study on high-speed tunable PT-symmetry vortex lasers facilitates the next generation of integrated optoelectronic devices for optical computing and communications in both classical and quantum regions.
基金This work was supported by the National Natural Science Foundation of China(Nos.61307050 and 61701271)the Natural Science Foundation of Shandong Province(No.ZR2016AM27)。
文摘In order to realize the ultrastrong absorption of graphene with electrical modulation properties, we designed a composite structure of graphene and parity-time(PT) symmetry photonic crystal, which is achieved by placing the graphene layer on the top layer of the PT symmetry photonic crystal. In this paper, the absorption properties of graphene and the electrical modulating properties of the structure were theoretically analyzed based on the transfer matrix method. The result shows that the proposed structure can achieve the absorption of 31.5 d B for the communication wavelength of 1550 nm;meanwhile,by setting the electric field intensity to ±0.02 V/nm, the absorption of graphene can be largely modulated to realize an electrically switchable effect, the modulation depth of graphene absorption can reach nearly 100%, and the operation speed is also close to 8.171 GHz. This investigation provides a novel approach to design graphene-based optoelectronic devices and optical communication devices.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12065022 and 12147213)。
文摘The dynamics of spin–orbit-coupled Bose–Einstein condensate with parity-time symmetry through a moving obstacle potential is simulated numerically. In the miscible two-component condensate, the formation of the Kármán vortex street is observed in one component, while ‘the half-quantum vortex street' is observed in the other component. Other patterns of vortex shedding, such as oblique vortex dipoles, V-shaped vortex pairs, irregular turbulence, and combined modes of various wakes, can also be found. The ratio of inter-vortex spacing in one row to the distance between vortex rows is approximately0.18, which is less than the stability condition 0.28 of classical fluid. The drag force acting on the obstacle potential is simulated. The parametric regions of Kármán vortex street and other vortex patterns are calculated. The range of Kármán vortex street is surrounded by the region of combined modes. In addition, spin–orbit coupling disrupts the symmetry of the system and the gain-loss affects the local particle distribution of the system, which leads to the local symmetry breaking of the system, and finally influences the stability of the Kármán vortex street. Finally, we propose an experimental protocol to realize the Kármán vortex street in a system.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11674119,11404125,and 11574389)the financial support from the Bird Nest Plan of HUST,Chinasupported by One Hundred-Talent Plan of Chinese Academy of Sciences
文摘Since the first observation of parity-time（PT） symmetry in optics, varied interesting phenomena have been discovered in both theories and experiments, such as PT phase transition and unidirectional invisibility, which turns PT-symmetric optics into a hotspot in research. Here, we report on the one-way localized Fabry-Pérot（FP） resonance, where a welldesigned PT optical resonator may operate at exceptional points with bidirectional transparency but unidirectional field localization. Overtones of such one-way localized FP resonance can be classified into a blue shifted branch and a red shifted branch. Therefore, the fundamental resonant frequency is not the lowest one. We find that the spatial field distributions of the overtones at the same absolute order are almost the same, even though their frequencies are quite different.
基金supported by the National Key R&D Program of China(Grant No.2017YFA0303700)the National Natural Science Foundation of China(Grant Nos.11634006,11934009,and 12074184)+1 种基金the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20191245)the State Key Laboratory of Acoustics,Chinese Academy of Sciences.
文摘Researches on parity-time(PT)symmetry in acoustic field can provide an efficient platform for controlling the travelling acoustic waves with balanced loss and gain.Here,we report a feasible design of PT-symmetric system constructed by piezoelectric composite plates with two different active external circuits.By judiciously adjusting the resistances and inductances in the external circuits,we obtain the exceptional point due to the spontaneous breaking of PT symmetry at the desired frequencies and can observe the unidirectional invisibility.Moreover,the system can be at PT exact phase or broken phase at the same frequency in the same structure by merely adjusting the external circuits,which represents the active control that makes the acoustic manipulation more convenient.Our study may provide a feasible way for manipulating acoustic waves and inspire the application of piezoelectric composite materials in acoustic structures.
基金Project supported by the National Natural Science Foundation of China(Grant No.11674036)the Beijing Youth Top-notch Talent Support Program,China(Grant No.2017000026833ZK08)the Fund of State Key Laboratory of Information Photonics and Optical Communications(Beijing University of Posts and Telecommunications)(Grant Nos.IPOC2016ZT04 and IPOC2017ZZ05)
文摘In this paper, the （l＋l）-dimensional variable-coefficient complex Ginzburg-Landau （CGL） equation with a parity- time （PT） symmetric potential U（x） is investigated. Although the CGL equations with a PT-symmetric potential are less reported analytically, the analytic solutions for the CGL equation are obtained with the bilinear method in this paper. Via the derived solutions, some soliton structures are presented with corresponding parameters, and the influences of them are analyzed and studied. The single-soliton structure is numerically verified, and its stability is analyzed against additive and multiplicative noises. In particular, we study the soliton dynamics under the impact of the PT-symmetric potential. Results show that the PT-symmetric potential plays an important role for obtaining soliton structures in ultrafast optics, and we can design fiber lasers and all-optical switches depending on the different amplitudes of soliton-like structures.
文摘We experimentally simulate a parity-time(PT)-symmetric quantum dynamics in a non-Hermitian system using a single-photon interferometer.We measure quantum final state using quantum state tomography.We observe the quantum state evolutions ranging from regions of unbroken to broken PT-symmetry using the single-photon interferometer.We experimentally prove that the eigenvalue of energy changes from real to imaginary corresponding to the non-Hermitian system from the PT-symmetry unbroken region to the PT-symmetry broken region.To the best of our knowledge,this is the first work to intuitively show the exceptional points of PT-symmetry non-unitary quantum dynamics in a single-photon interferometer from the energy perspective.
基金the National Natural Science Foundation of China(Grant Nos.12025401 and U1930402).
文摘We experimentally investigate the impact of static disorder and dynamic disorder on the non-unitary dynamics of parity-time(PT)-symmetric quantum walks.Via temporally alternating photon losses in an interferometric network,we realize the passive PT-symmetric quantum dynamics for single photons.Controllable coin operations allow us to simulate different environmental influences,which result in three different behaviors of quantum walkers:a standard ballistic spread,a diffusive behavior,and a localization,respectively,in a PT-symmetric quantum walk architecture.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11674119 and 11690032)the Fundamental Research Funds for the Central Universities,China(HUST:2019JYCXJJ038)X.F.Z.and P.C.C.acknowledge the financial support from the Bird Nest Plan of HUST.
文摘Parity-time (PT) symmetry/anti-parity-time (APT) symmetry in non-Hermitian systems reveal profound physics andspawn intriguing effects. Recently, it has been introduced into diffusive systems together with the concept of exceptionalpoints (EPs) from quantum mechanics and the wave systems. With the aid of convection, we can generate complex thermalconductivity and imitate various wavelike dynamics in heat transfer, where heat flow can be “stopped” or moving against thebackground motion. Non-Hermitian diffusive systems offer us a new platform to investigate the heat wave manipulation.In this review, we first introduce the construction of APT symmetry in a simple double-channel toy model. Then we showthe phase transition around the EP. Finally, we extend the double-channel model to the four-channel one for showing thehigh-order EP and the associated phase transition. In a general conclusion, the phase difference of adjacent channels isalways static in the APT symmetric phase, while it dynamically evolves or oscillates when the APT symmetry is broken.
基金supported by the National Natural Science Foundation of China under 61535012 and 61522509supported by the National High-Tech Research and Development Program of China under 2015AA017102supported in part by the Thousand Young Talents Program.
文摘Symmetry plays a crucial role in explorations of the laws of nature.Parity-time(PT)symmetry phenomena can lead to entirely real spectra in non-Hermitian systems,which attracts considerable attention in the fields of optics and electronics because these phenomena provide a new tool for the manipulation of oscillation modes and nonreciprocal signal transmission.A potential new field of application is microwave photonics,an interdisciplinary field in which the interaction between microwaves and optical signals is exploited.In this article,we report the experimental use of PT symmetry in an optoelectronic oscillator(OEO),a key microwave photonics system that can generate singlefrequency sinusoidal signals with high spectral purity.PT symmetry is theoretically analyzed and experimentally observed in an OEO with two mutually coupled active oscillation cavities via a precise manipulation of the interplay between gain and loss in the two oscillation cavities.Stable single-frequency microwave oscillation is achieved without using any optical/electrical filters for oscillation mode selection,which is an indispensable requirement in traditional OEOs.This observation opens new avenues for signal generation and processing based on the PT symmetry principle in microwave photonics.
基金National Key Research and Development Program of China(2018YFA0701902)National Natural Science Foundation of China(62071055,62135014)。
文摘In recent years,parity-time(PT)symmetry in optoelectronic systems has been widely studied,due to its potential applications in lasers,sensors,topological networks,and other fields.In this paper,a time-division multiplexed pulsed optoelectronic oscillator(OEO)is proposed to study the dynamics of a PT symmetry system.Two microwave pulses are used to realize the PT symmetry in a single spatial resonator based on the temporal degrees of freedom.The gain and loss of the microwave pulses and the coupling coefficient between them can then be controlled.We first demonstrate the phase diagram from PT broken to PT symmetry in the OEO system.We theoretically prove that the perturbation of a coupling-induced phase shift larger than(2π)×10^(-2)causes the disappearance of the PT symmetry.In this experiment,the perturbation is less than(2π)×0.5×10^(-2);thus,the phase transition of PT symmetry is observed.In addition,multipairs of PT-symmetry pulses indicate that pulsed OEO could be used to implement complex non-Hermitian Hamilton systems.Therefore,it is confirmed that pulsed OEO is an excellent platform to explore the dynamics of PT symmetry and other non-Hermitian Hamiltonian systems.
基金supported by the National Natural Science Foundation of China(61860206002,61905095,61805103).
文摘Parity-time(PT)symmetry has attracted intensive research interest in recent years.PT symmetry is conventionally implemented between two spatially distributed subspaces with identical localized eigenfrequencies and complementary gain and loss coefficients.The implementation is complicated.In this paper,we propose and demonstrate that PT symmetry can be implemented between two subspaces in a single spatial unit based on optical polarimetric diversity.By controlling the polarization states of light in the single spatial unit,the localized eigenfrequencies,gain,loss,and coupling coefficients of two polarimetric loops can be tuned,leading to PT symmetry breaking.As a demonstration,a fiber ring laser based on this concept supporting stable and single-mode lasing without using an ultranarrow bandpass filter is implemented.
基金National Natural Science Foundation of China(61805090, 62075075)National Key Research and Development Project of China (2018YFB2201901)。
文摘Encircling an exceptional point(EP) in a parity-time(PT) symmetric system has shown great potential for chiral optical devices,such as chiral mode switching for symmetric and antisymmetric modes.However,to our best knowledge,chiral switching for polarization states has never been reported,although chiral polarization manipulation has significant applications in imaging,sensing,communication,etc.Here,inspired by the anti-PT symmetry,we demonstrate,for the first time to our best knowledge,an on-chip chiral polarizer by constructing a polarization-coupled anti-PT symmetric system.The transmission axes of the chiral polarizer are different for forward and backward propagation.A polarization extinction ratio of over 10 dB is achieved for both propagating directions.Moreover,a telecommunication experiment is performed to demonstrate the potential applications in polarization encoding signals.It provides a novel functionality for encircling-an-EP parametric evolution and offers a new approach for on-chip chiral polarization manipulation.
基金Project supported by the National Natural Science Foundation of China(Grant No.11802003).
文摘This paper studies two-lane asymmetric simple exclusion processes(ASEPs)with an intersection.In the upstream segments of the intersection,one particle can move to the next site with rate 1 if the site is empty,and the other particle can move forward with rate p in the sites of downstream segments.The parameter p can represent the rate of slowing of motion,and the parameter is introduced to investigate spontaneous symmetry breaking(SSB)phenomenon.Extensive Monte Carlo simulations are carried out.It is shown that three symmetric phases exist and the SSB does not exist in the system.Simple mean field approach in which correlation of sites is ignored is firstly adopted to analyze the system,and the system is divided into four independent segments.It is found that the analytical results deviate from the simulation ones,especially when p is small.In addition,the inexsitence of SSB can only be explained qualitatively.Motivated by this,we carry out the cluster mean field analysis in which correlation of five sites is considered.It is shown that densities of the two upstream segments are equal,which demonstrates that the SSB does not exist.It is also shown that,as expected,the cluster mean field analysis performs much better than the simple mean field analysis.
基金Project supported by the National Natural Science Foundation of China (Grant No. 12304201)。
文摘The conditions for the emergence of the non-Hermitian skin effect, as a unique physical response of non-Hermitian systems, have now become one of the hot research topics. In this paper, we study the novel physical responses of nonHermitian systems with anomalous time-reversal symmetry, in both one dimension and two dimensions. Specifically, we focus on whether the systems will exhibit a non-Hermitian skin effect. We employ the theory of generalized Brillouin zone and also numerical methods to show that the anomalous time-reversal symmetry can prevent the skin effect in onedimensional non-Hermitian systems, but is unable to exert the same effectiveness in two-dimensional cases.
