Topological Waveguide Research Articles

Observation of temporal optical solitons in a topological waveguide.

Photonic topological systems may be exploited in topological quantum light generation, the development of topological lasers, the implementation of photonic routing systems and optical parametric amplification. Here, we leverage the strong light confinement of an ultra-silicon-rich nitride (USRN) topological waveguide adopting the 1D Su-Schrieffer-Heeger (SSH) system with a topological domain wall. We present the formation and propagation of temporal optical solitons in the topological waveguide, exhibiting two-fold temporal compression. We further observe a saturation in the output power at sufficiently high input powers. It is further observed that pulse propagation through a trivial, non-topological waveguide does not lead to similar temporal soliton dynamics. The demonstrated topological system allows for the temporal compression to be manipulated through power tuning via topological control of delocalization of the topological mode. This design degree of freedom allows temporal solitons to be generated in a topological waveguide while providing straightforward control of temporal pulses in practical applications.

All-optical switching in nonlinear topological waveguide arrays.

Photonic topological states are prospective in integrated optical devices due to their robustness to perturbations and defects. When taking into account the nonlinear effects of the system, the functionality of topological photonics can be further enhanced. Here, we investigated the interplay between topological edge states and nonlinear effects based on the Su-Schrieffer-Heeger (SSH) model. Relying on the theory prediction that topological edge states would shift upward under the action of nonlinearity, two types of optical switching are designed and experimentally realized in femtosecond laser direct-write waveguide arrays. This work provides a new, to the best of our knowledge, approach to preparing all-optical switches and offers a new perspective on the application of nonlinearity in topological optical devices.

Topological elastic wave transport and manipulation in three-dimensional metamaterials stacked with sandwich plates

Topological metamaterials demonstrate unprecedented wave manipulation abilities with topologically protected robustness, which have been extensively investigated in one-dimensional (1D) and two-dimensional (2D) mechanical systems, but less explored in three-dimensional (3D) systems. In this study, a 3D topological mechanical metamaterial with periodically stacked sandwich metamaterial plates is proposed to achieve 2D topological surface wave transport in a relatively low-frequency range. An innovative chiral compression-torsion coupling core is employed on the sandwich metamaterial plate to lower the band frequency. Analogous to the quantum valley Hall effect, the two-fold topological nodal line is lifted by breaking the spatial inversion symmetry, opening a topological band gap. By supercell analysis, the topological interface state is demonstrated to appear at the interface of two topologically different domains, and the topological boundary state can also be excited under appropriate free or fixed boundary conditions. Taking advantage of the 3D periodicity, the wave propagation based on both topological interface states and boundary states is examined in both 2D flat plates and 3D structures, realizing 1D topological waveguide and 2D topological surface wave transport respectively. It is found that mode symmetry matching is crucial for constructing the topological wave transport with both interface and boundary states. Leveraging the dependence of boundary states on boundary conditions, this work innovatively presents route-switchable and layer-selective wave manipulation by controlling boundary conditions without complicated structure design, enriching the strategies for tunable elastic wave manipulation. Besides, the topologically protected surface wave transport is demonstrated by introducing defects and disorders. These findings provide new insights into the topological transport of elastic waves in 3D mechanical metamaterials and contribute to the development of intelligent and robust devices for various purposes, such as vibration mitigation, energy harvesting, and signal sensing.

Opto-induced topological waveguide transport in metaplates

Opto-induced topological waveguide transport in metaplates

Multiband topological acoustic waveguide with multistage toroidal resonant cavities

In recent years, there has been significant development in acoustic waveguides through the introduction of topological phase correlation concepts in acoustics. Many studies have shown the properties of acoustic unidirectional transmission. This paper presents a new ring-shaped acoustic topological insulator that is multi-band, unlike previous structures. The structure improves internal space utilization with the same dimensions, reducing acoustic wave conduction frequency in air environments. Additionally, the introduction of a multistage ring-shaped resonant cavity enables the conduction of acoustic waves in multiple frequency bands. This paper employs the rotational scattering mechanism to invert the topological phase of the lattice. This allows for the construction of two crystals with opposite phases, which can be used to create a topological channel for the transmission of acoustic waves. At the topological interface, the acoustic transmission losses within the four bands are small. Furthermore, this paper verifies by simulation that the defects have little effect on acoustic transmission. The paper's research offers potential for multiband acoustic control.

Topological valley waveguide state transport based on the nesting difference

Acoustic topological waveguide states are characterized by topologically protected transport. Existing acoustic topological valley-locked waveguide state transport structures can only realize single-scene acoustic field modulation due to the limitation of structural tunability, and it is difficult to realize width degree of freedom and reconfigurable transport paths of acoustic waves by adjusting the transport structure for complex acoustic field. Therefore, the transport structures become a conceptualized idea in terms of tunability. Our study introduces a nesting method in the design of the sonic crystal scatterer, which splits the scatterer structure into a removable outer shell and a core, and three topological phase transitions can be realized by only changing the nesting method of the sonic crystal shell, this approach constructs a fully reconfigurable topological waveguide. The results demonstrate that changing the nesting of the sonic crystals induces effective spatial inversion symmetry breaking, which leads to the valley topological phase transitionSimulations and experiments demonstrate that this transport structure has excellent robust transport properties with large inflection corners, and it is capable of realizing acoustic focusing, acoustic channeling, and acoustic logic gates. This fully reconfigurable sonic crystal design method can provide implications for the modulation of other classical waves.

Topologically protected bound modes in non-neighboring hexagonal lattices

In the last decade, the study of wave localization and guiding has gained a renewed interest thanks to the introduction of the concept of topological protection. Originally developed in the field of quantum mechanics, topological protection has successively inspired the search for its analogue in other physical domains, including elasticity. In this context, periodic hexagonal lattices have been proposed as ideal candidates to realize these concepts. In this work, we explore the dynamic behavior of discrete hexagonal lattices with third nearest neighbor connections. First, the formation and transition of multiple Dirac cones above a critical value of the relative stiffness between the first and third nearest neighbor connections is derived. Then, the formation of extremely localized modes (i.e., bound modes) at the interface between regions formed by lattices which are inverted copies of each other is demonstrated. Our results show that this localization derives from a type of interface satisfying a point reflection symmetry for which the considered chain decouples into two identical copies at the high symmetry point of the Brillouin zone. Our findings open novel avenues for topological waveguiding and confinement with potential applications in surface acoustic wave devices.

Broadband large-scale acoustic topological waveguides

The acoustic topological waveguide (ATW) hosting topologically protected waveguide modes provides a unique opportunity for achieving large-scale sound transport with robustness. However, prevailing ATWs are typically designed by forward-designed sonic crystals (SCs) based on physical intuitions, unavoidably leading to restricted bandwidths. Here, using the inverse-designed SCs with maximized topological bandgaps, we construct broadband ATWs based on both the quantum spin Hall effect and the quantum valley Hall effect. Broadband large-scale transportation, spin-locked one-way transportation, and the squeezing effect of acoustic waves are demonstrated. This study ushers a new path for designing topological devices with broadband performance for large-scale acoustic wave transportation.

Dual-band topological refractive properties in solid phononic crystals

The lossless transmission of topological edge states and the robustness of defect immunity make topological refractive materials have important application prospects in acoustic communication and integrated acoustic devices. However, most topological refractive materials only have a single operating frequency band, which obviously limits their application in multi-band and multi-function devices. Therefore, a phononic crystal with dual-frequency topological states is designed in this paper, and its dual-topological refractive properties are investigated and discussed. The existence of in-plane bulk elastic wave edge states is demonstrated by calculating the band structure of supercell comprising phononic crystals with different topological phases. Numerical simulations of the constructed acoustic topological waveguide are performed and negative refraction is observed at the low bandgap while zero refraction is observed at the high bandgap. Then, the topological zero refraction is investigated for different incidence angles. The designed dual-band acoustic topological insulator has potential applications in multi-band acoustic communication and acoustic information processing.

Temperature tunability of topological phase transitions and edge states in two-dimensional acoustic topological insulators

Topological insulators are characterized by exhibiting an internal insulating state but a surface conductor state, which makes them advantageous for applications in novel devices. However, for most given acoustic topological metamaterials, the operating frequency is relatively fixed and the effect of temperature on their topological properties is rarely considered. Therefore, a temperature-tunable acoustic topological insulator is constructed in this paper. The quadruple degenerate Dirac cone formed at Γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma$$\\end{document} point can be opened by adjusting the temperature, causing topological band inversion between the doubly degenerate dipolar and quadrupole states, and achieving topological phase transition. The evolution of its topological state with temperature is numerically investigated and a novel topological acoustic waveguide is constructed. The switching effect of temperature on the waveguide device is verified by numerical simulation and experiment. Non-contact active modulation of edge states in the structure is achieved by temperature-controlled topological phases, exhibiting acoustic switching effects. This study can provide corresponding references for the intelligent control of acoustic topology in noise, vibration, and other aspects.

Reconfigurable acoustic topological valley-locked waveguide states transport based on nestable sonic crystals

Topological waveguide states in condensed matter physics systems show significant potential for applications, such as high-capacity information communication and energy regulation of complex physical fields owing to the phenomenon of large-area wave transport. The lack of tunability design for sonic crystals makes it difficult to change the structure and function of existing topological waveguide states transport structures after sample fabrication, especially in terms of the freedom of width and tunability on the transport path, and thus hinders further engineering applications of topological waveguide states. To address these challenges, the design method based on nested difference theory to achieve topological phase transitions in sonic crystals is proposed, which in turn leads to the construction of fully reconfigurable acoustic topological waveguide states and explores their potential applications. Firstly, a reconfigurable nested scatterer structure is designed, which is split into a snowflake-like core and an outer shell. This scatterer is demonstrated to be able to break the spatial inversion symmetry and realize the transition of sonic crystals between three valley topological phases by only changing the nesting mode of the nested outer shell. Based on reconfigurable sonic crystals, the fully reconfigurable acoustic topological valley-locked waveguide states are constructed. Simulations and experiments further confirm that such waveguides are characterized by high-capacity transport, acoustic focusing, and robust transport over large inflection corners. In addition, we explore the potential applications of reconfigurable waveguides for acoustic channels and acoustic logic gates. The precise distribution of the waveguide states energy is achieved in the acoustic channel by adjusting the rotation angle of the channel. Moreover, the logical computational relationships of the transport structure of the topological waveguide states are determined using different acoustic excitation modes. The excellent transport properties generated by fully reconfigurable acoustic topological waveguide states will have potential applications in both field enhancement and energy harvesting. This provides the possibility for the development of novel acoustic devices capable of modulating waves in complex physical scenarios.

Frequency-selective valley-edge transmission and channeling in phononic-crystal plates with dual topological modulations

In this numerical study, we propose dual-modulated topological pillared phononic crystal (PnC) plates and demonstrate their application in achieving frequency-selective waveguiding of Lamb-wave valley-edge states. We show that both the radius and the height of the pillars in the honeycomb unit cell can be varied, allowing a generalized parameter space to obtain the complete topological bandgaps and two groups of distinct valley Hall phases for designing topological waveguides operating in different frequency ranges. Accordingly, we construct different types of phase domain walls to support valley-edge states using the dual-modulated PnC plates with a lattice constant of 2000 μm and with topological bandgaps opened around the Dirac cone frequency of 426 kHz. The numerical results show that the valley-edge states emerge to cover different frequency ranges and exhibit robust backscattering immunity when propagating along zigzag paths with sharp corners. Furthermore, the transport path of the valley-edge states can be designed to be highly dependent on the operating frequency in different domain walls. Consequently, we design a straight waveguide and three multichannel waveguides to demonstrate frequency-dependent switchable transmission and selective channeling of valley-edge states, respectively. The results of this study pave the way for the development and optimization of topological acoustic circuits using the generalized parameter space approaches and are expected to find promising applications in frequency-controlled and signal-division devices.

Achievement splitting for topological states with pseudospin in phase modulation by using gyromagnetic photonic crystals

As we know, valley-Hall kink states or pseudospin helical edge states are excited by polarized-momentum-locking [left-handed circular polarization (LCP) and right-handed circular polarization (RCP)] because the valley-Hall kink modes or pseudospin polarized modes have intrinsic and local chirality, which is difficult for these states to achieve phase modulation. Here we theoretically design and study a compatible topological photonic system with coexistence of photonic quantum Hall phase and pseudospin Hall phase, which is composed of gyromagnetic photonic crystals with a deformed honeycomb lattice containing six cylinders. A typical kind of hybrid topological waveguide states with pseudospin-characteristic, magnetic field-dependent, and strong robustness against backscattering and perfect electric conductor (PEC) is realized in the present system. Furthermore, we re-design a structure with intersection-liked, achieve splitting for one-way pseudospin quantum Hall edge states by using phase modulation. Robustness of the one-way pseudospin-quantum Hall edge states in splitting has been demonstrated as well. Additionally, PEC inserted in transport channel brings optical path difference in waveguide transmission, which would influence splitting for hybrid topological waveguide states in phase difference modulation. This work not only provides a new way for manipulation (i.e., phase modulation) of hybrid topological waveguide states in compatible topological photonic system from distinct topological classes but also has potential in various applications, such as sensing, signal processing, and on-chip communications.

Square-root topological insulator for a dual-band photonic waveguide

We show that square-root topological insulators can be utilized as a platform for dual-band topological waveguides in 2-dimensional photonic crystals. Valley states for each of two frequency band gaps in differently perturbed decorated honeycomb lattices have opposite directions of the phase rotations, revealing opportunities for dual-band unidirectional topological valley transport. The topological valley edge states exist at the boundary between differently perturbed photonic crystals in the two frequency bands. In addition, unidirectional, and robust propagation of electromagnetic waves along the boundary in the two frequency bands are numerically performed. Our work provides extensions of square-root topological insulators to robust, unidirectional, and dual-band photonic waveguides.

Dual-band topological large-area waveguide transport in photonic heterostructures

Dual-band topological large-area waveguide transport in photonic heterostructures

Terminal-Matched Topological Photonic Substrate-Integrated Waveguides and Antennas for Microwave Systems.

In engineered photonic lattices, topological photonic (TP) modes present a promising avenue for designing waveguides with suppressed backscattering. However, the integration of the TP modes in electromagnetic systems has faced longstanding challenges. The primary obstacle is the insufficient development of high-efficiency coupling technologies between the TP modes and the conventional transmission modes. This dilemma leads to significant scattering at waveguide terminals when attempting to connect the TP waveguides with other waveguides. In this study, a topological photonic substrate-integrated waveguide (TPSIW) is proposed that can seamlessly integrate into traditional microstrip line systems. It successfully addresses the matching problem and demonstrates efficient coupling of both even and odd TP modes with the quasi-transverse electromagnetic modes of microstrip lines, resulting in minimal energy losses. In addition, topological leaky states are introduced through designed slots on the TPSIW top surface. These slots enable the creation of TP leaky-wave antennas with beam steering capabilities. A wireless link based on TPSIWs are further established that enables the transmission of distinct signals toward different directions. This work is an important step toward the integration of TP modes in microwave systems, unlocking the possibilities for the development of high-performance wireless devices.

Ultrabroadband valley transmission and corner states in valley photonic crystals with dendritic structure

In photonic crystal systems, topologically protected edge states and corner states can be achieved by breaking spatial inversion symmetry, which is expected to be applied to topologically protected lasers, optical communication and integrated photonics. However, designing ultrabroadband topological photonic crystals is still a challenge. In this work, we propose a valley photonic crystal composed of dendritic structures, which can realize valley transmission with a relative bandwidth up to 59.65%. Compared with the previously reported two-dimensional broadband photonic crystals with 32.02% bandwidth, the relative bandwidth of the proposed valley transmission is increased by almost 100%. Theoretical analysis, numerical simulation and experimental measurement all confirm flexible manipulation of electromagnetic wave propagation paths. Ultrabroadband topological waveguides with the zigzag and armchair interface are demonstrated, which can achieve experimentally 58.71% and 36.78% relative bandwidth, respectively. In addition, several topological channel intersections are designed. Finally, two types of corner states with valley switchability and selectivity are demonstrated.

On Klein tunneling of low-frequency elastic waves in hexagonal topological plates

Incident particles in the Klein tunnel phenomenon in quantum mechanics can pass a very high potential barrier. Introducing the concept of tunneling into the analysis of phononic crystals can broaden the application prospects. In this study, the structure of the unit cell is designed, and the low frequency (< 1 kHz) valley locked waveguide is realized through the creation of a phononic crystal plate with a topological phase transition interface. The defect immunity of the topological waveguide is verified, that is, the wave can propagate along the original path in the cases of impurities and disorder. Then, the tunneling phenomenon is introduced into the topological valley-locked waveguide to analyze the wave propagation, and its potential applications (such as signal separators and logic gates) are further explored by designing phononic crystal plates. This research has broad application prospects in information processing and vibration control, and potential applications in other directions are also worth exploring.

Topological and conventional nanophotonic waveguides for directional integrated quantum optics

Directionality in integrated quantum photonics has emerged as a promising route towards achieving scalable quantum technologies with nonlinearities at the single-photon level. Topological photonic waveguides have been proposed as a novel approach to harnessing such directional light-matter interactions on-chip. However, uncertainties remain regarding the strength of the directional coupling of embedded quantum emitters to topological waveguides in comparison to conventional line defect waveguides. In this work we present an investigation of directional coupling in a range of waveguides using a combination of experimental, theoretical, and numerical analyses. We quantitatively characterize the position dependence of the light-matter coupling on several topological photonic waveguides and benchmark their directional coupling performance against conventional line defect waveguides. We conclude that topological waveguides underperform in comparison to conventional line defect waveguides, casting their directional optics credentials into doubt. To demonstrate this is not a question of the maturity of the field; we show that state-of-the-art inverse design methods, while capable of improving the directional emission of these topological waveguides, still place them significantly behind the operation of a conventional (glide-plane) photonic crystal waveguide. Our results and conclusions pave the way towards improving the implementation of quantitatively predicted quantum nonlinear effects on-chip. Published by the American Physical Society 2024

Robust high capacity in-plane elastic wave transport in 2D chiral metastructures

Novel 2D tri-chiral metastructures with mass inclusion are proposed in this work. Compared to conventional 2D honeycomb metastructures, these superior metastructures have a wide in-plane low-frequency bandgap (BG) and single Dirac cone (DC) simultaneously. Ligament width and inclusion density are both key factors for tuning the DC and low-frequency BGs. Due to the superior dispersion properties, metamolecules analog of quantum spin Hall effects (QSHEs) are built by the band folding method, and topological phase transition is obtained by shrinking/expanding distance between the mass inclusion and metamolecule center. Topological interface states (TISs) are observed between the two domains with distinct topological properties. To further enhance energy capacity of in-plane elastic wave transport, a 2D heterostructure is constructed by doping waveguiding layer at the topological interface. As expected, robust high capacity in-plane elastic wave transport is realized, named as topological waveguide states (TWSs). While TWS velocity remains unaffected, an increasing number of waveguiding layers additionally leads to a reduced bandgap width and transition from TWSs to conventional edge states (CESs). Average transmitted energy is also observed to increase almost linearly with the thickness of waveguide layer. By virtue of the robust high-capacity wave transport, two potential applications for energy focusing and beam splitting are clearly demonstrated. Besides, the temperature field is introduced into the 2D topological heterostructure to widen the operating frequency of TWSs. Fortunately, TWSs can be tuned to the lower frequency range by increasing temperature, and retain gapless and high-capacity characteristics. Last but not least, we demonstrate that temperature can be used as a switch for in-plane topological wave transport. The proposed 2D chiral metastructures have great potentials to serve as building blocks for multifunctional topological devices.