Multimode Coupling Research Articles

Design theory for section model tests considering multimode coupling and imperfect modeshape similarity of full bridges

Section model tests are the most fundamental wind-tunnel technique widely employed in the design of flexible cable-supported bridges. To guarantee the accuracy of aeroelastic stability assessment, the dynamic behavior of a section model test should reflect the aeroelastic characteristics of the full bridge. Conventional method only employs the fundamental vertical and torsional modes for the design of dynamic parameters, typically ignoring multimode coupling effect and assuming perfect modeshape similarity. This paper introduces a novel theoretical framework that integrates multimode coupling and imperfect modeshape similarity into the design of a section model test. The framework establishes a direct equivalence between the complex modal parameters of the unstable mode in the multimode coupling system and the two degrees-of-freedom coupling system of the section model. It quantifies each mode's contribution to coupled flutter through a single parameter denoted as mode participation factor. Validation of this improved design theory is performed using numerical models of four representative cable-supported bridges, highlighting its effectiveness. The study also sheds light on the complexities of multimode aeroelastic coupling and the limitations of section model tests.

Research on the influence of cutter overhang length on robotic milling chatter stability

Serial industrial robots are widely in demand in the field of large-scale component processing and manufacturing. However, the structure characteristic of serial robots makes it easy to generate chatter during milling and the overhang length of milling cutter has an important influence on the stability of robotic milling. Milling cutter overhang length refers to the length from the tip of the cutter to the protrusion of the spindle, to study the influence of milling cutter overhang length on the stability behavior of robotic milling, the modal parameters of milling cutter under different overhang length were obtained by hammer experiment, and its dynamic characteristics were analyzed. The stability behavior for robotic milling under different cutter overhang lengths was analyzed by using the stability lobe diagrams, and the stability lobe diagrams were verified by robotic milling experiments. The results show that the rigidity and natural frequency of milling cutter decrease with the increase of overhang length. There is a big gap between the stability lobe diagrams and the actual machining state when the cutter overhang length is short, and the low frequency vibration is easy to occur in the robotic milling process when the spindle speed is low, which is most probably because that the absorbed vibration energy by the cutter has been transferred to the robot body before the milling cutter vibrates. When the cutter overhang is increased and the feed direction is along the y-axis of the robot global coordinate system, the stability lobe diagrams by considering the multi-mode coupling effect is more consistent with the actual milling state.

Ultra-broadband multimode fiber-to-chip edge coupler based on periodically segmented waveguides.

Mode-division multiplexing (MDM) technology demonstrates a bright outlook for enhancing the capacity of chip-scale or fiber-based optical communication. Nevertheless, the fiber-to-chip MDM optical interconnects are hindered by the considerable mode mismatch and inter-modal cross talk between the few-mode fiber (FMF) and on-chip few-mode waveguide (FMW). In this Letter, a new, to the best of our knowledge, multimode coupling solution based on periodically segmented waveguides for the MDM system is proposed, which achieves efficient conversion between LP01, LP11a, and LP11b modes in FMF and E11, E21, and E12 modes in FMW with low refractive index difference. The simulation results show that the coupling loss is less than 0.41, 0.27, and 0.90 dB for the three modes, over the wavelength range of 1100-1800 nm. The fabricated device based on a polymer platform shows low fiber-to-chip coupling losses of less than 1.8, 1.7, and 3.0 dB, respectively, over a 130 nm wavelength. The presented scheme provides a competitive solution for realizing the ultra-efficient integration of prospective fiber-chip optical interconnections and communications.

Energy consumption analysis of trains based on multi-mode virtual coupling operation control strategies

Urban rail transit, as a main mode of travel, has always been concerned with the balanced relationship between energy consumption and transport efficiency. The advent of the virtually coupled train set (VCTS) has significantly enhanced the efficiency of existing railway lines. Both energy consumption and comfort during the operation of VCTS control technology have emerged as significant challenges for the development of VCTS since the inception of onsite testing. A review of the current research status of VCTS control systems has revealed that the majority of current formation control systems are focused on the safe operation of formation trains, the stability of train control systems, and safe train separation models. However, a case study has shown there is a strong correlation between train operating intervals, train control strategies, and train operating energy consumption. Therefore, it is necessary to design and plan the operation modes of formation trains for different train operation requirements. This paper presents four distinct control modes, developed through the integration of the most prevalent VCTS control strategies, operational modes, and operational requirements. The design of these control modes is guided by considerations of energy consumption, safety, and comfort during train operation. A case study of Beijing Subway Line 11 revealed a significant correlation between energy consumption, control mode, and safety under different control modes. In particular, the correlation between train running intervals and energy consumption in a high-precision tracking state provides valuable technical support for the future operation of VCTS technology in different periods, scenarios, and environments.

Multimode vibrational coupling across the insulator-to-metal transition in 1T-TaS2 in THz cavities.

The use of optical cavities on resonance with material excitations allows controlling light-matter interaction in both the regimes of weak and strong coupling. We study here the multimode vibrational coupling of low energy phonons in the charge-density-wave material 1T-TaS2 across its insulator-to-metal phase transition. For this purpose, we embed 1T-TaS2 into THz Fabry-Pérot cryogenic cavities tunable in frequency within the spectral range of the vibrational modes of the insulating phase and track the linear response of the coupled phonons across the insulator-to-metal transition. In the low temperature dielectric state, we reveal the signatures of a multimode vibrational strong collective coupling. The observed polariton modes inherit character from all the vibrational resonances as a consequence of the cavity-mediated hybridization. We reveal that the vibrational strong collective coupling is suppressed across the insulator-to-metal transition as a consequence of the phonon-screening induced by the free charges. Our findings emphasize how the response of cavity-coupled vibrations can be modified by the presence of free charges, uncovering a new direction toward the tuning of coherent light-matter interaction in cavity-confined correlated materials.

Polarization-dependent near-field coupling and far-field harmonic modulation in a graphene-based plasmonic nanostructure

The interplay between light and matter has fostered innovative research in surface plasmons, specifically in graphene, due to its tunable Fermi energy and reduced losses in the infrared and terahertz spectra. This study explores the anisotropic coupling of nonlocalized surface plasmons in graphene with localized magnetic polaritons (MP) in a silicon carbide (SiC) array. By adjusting graphene’s Fermi energy and polarization angle, we successfully achieved hybrid coupling, giving rise to three clearly distinguishable hybridized states. Using the coupled oscillator model as a framework, we conducted an analysis of the intricate multimode coupling and accurately ascertained the weighting efficiencies of the individual modes comprising the hybrids. By integrating the design principles of space-time coding metasurfaces, we successfully broadened the scope of the application, extending its reach from the near-field to the far-field. These novel discoveries pave new paths for advancements in thermal emitters, photonic systems, energy conversion technologies, and the creation of cutting-edge plasmonic devices.

Enhancements to quantum communication performance utilizing a prototype photonic lantern and multiplexed single-photon detection.

The optical interfacing between a free-space channel and single-photon detectors (SPDs) can greatly impact the inherent performance of a free-space quantum key distribution receiver. Direct coupling to detectors creates engineering challenges, and a single-mode fiber requires adaptive optics. Using a multimode fiber (MMF) is common; however, larger core diameters limit the achievable bandwidth. We demonstrate a prototype multimode fiber-based photonic lantern that allows us to retain the benefits of the large multimode coupling while transitioning to multiple, less multimodal fibers, reducing bandwidth limitation.

Lateral and vertical spin-wave transport in a multimode magnonic ring coupler

Lateral and vertical spin-wave transport in a multimode magnonic ring coupler

Multi-mode coupling in a H-shaped metamaterial structure in terahertz frequency

Mode coupling can not only effectively control the frequency, amplitude and linewidth of the transmission spectrum, but also improve the Q-factor of the spectrum. Herein, we propose a H-shaped metamaterial, in which the dipole mode, LC mode and lattice mode can be excited selectively, and each mode frequency can be independently tuned by changing the polarization of incident THz wave as well as the lattice constant of the metamaterial structure, thus allowing greater degrees of freedom to customize the polarization components of different properties in the system. Under different polarization directions, the strong coupling between the lattice mode and the inductance-capacitance (LC) mode as well as the lattice mode and the dipole mode is realized, which makes the transmission resonance Q-factor of the hybrid state increase to 8 times that of the single resonance state, and the obvious anti-crossing phenomenon is observed. In addition, the LC mode and the dipole mode can be excited simultaneously, and the coupling between these two modes successfully excites a bound states in the continuum with an infinite Q-factor.

Hybrid magneto-plasmonic structure consisting of hexagonal periodic nanodisks array with giant transverse magneto-optical Kerr effect for sensing application

The present study proposes a theoretical design of the magneto-optical surface plasmon resonance (MOSPR) refractive index sensor that utilizes a magnetic field for modulating the dispersion of surface plasmon. This sensor based on the transverse magneto-optical Kerr effect (TMOKE) is constructed using a hybrid magneto-plasmonic film covered with an array of hexagonal periodic Au nanodisks. The structural parameters were optimized to obtain the Fano shape TMOKE response characterized by an extremely narrow bandwidth (0.00997°) and remarkably high amplitude (0.99). The excitation of the optimal surface plasmon resonance (SPR) and the resonance enhancement effect of multi-mode coupling enables us to achieve a surface sensitivity of 207.5 deg RIU−1 and a high figure of merit of the order of 104 RIU−1, surpassing conventional SPR and MOSPR sensors by at least one order of magnitude. The present study offers a comprehensive guideline for the design of high-performance magneto-plasmonic sensors, facilitating instrument miniaturization and manufacturing cost reduction.

The anion photoelectron spectrum and diabatization of tetrazolyl.

The potential energy surface of tetrazolyl [cyclic (N4CH)] has a conical intersection seam between the two lowest-energy electronic states near the ground state minimum geometry. This work treats that molecule. The potential energy surfaces used in this study are based on a least-squares fitting procedure that includes abinitio energies, energy gradients, and derivative couplings described using polynomials up to fourth-order and abinitio data obtained from multireference configuration interaction wave functions. A five-electronic-state description was generated with a root mean square absolute energy error of 9.6cm-1, compared to 326.8cm-1 when only second-order terms were used. The time-independent multimode vibronic coupling in the KDC approximation was used to simulate and analyze the anion ultraviolet photoelectron spectrum of tetrazolide.

Structural design and coupling analysis of multimode variable coupling parallel mobile robots

Purpose There is coupling between the branches of mobile parallel robots, similar to traditional parallel mechanisms, but there is currently relatively little research on the coupling problem between the branches of mobile parallel robots. Design/methodology/approach This study optimizes the coupling analysis method of traditional parallel mechanisms, treats the mobile parallel mechanism as a whole, takes the motion of the active pair as input and the overall motion of the mobile parallel mechanism as output and analyzes the input–output characteristics of the mobile parallel mechanism. Moreover, this study applies this theory to a mobile parallel mechanism, designs control logic and finally conducts simulation and physical verification. Findings This study proposes a coupling analysis method suitable for parallel mobile robots and designs the control logic of their active pair based on the results of their coupling analysis. This study designs a multimode variable coupling parallel mobile robot, which can change the coupling of the mechanism by changing its own branch chain structure, so that it can switch between different coupling configurations to meet the different needs brought by different terrains. Originality/value The work presented in this paper propose a method for analyzing the coupling of mobile parallel robots and simplify their control logic by applying coupling theory to the design of mobile parallel robots. This study conducts simulation and physical experiments, thereby filling the gap in the coupling analysis of parallel mobile robots and laying the foundation for the research of uncoupled parallel mobile robots.

Broadband Janus-Helmholtz transducer with various liquid cavity resonances

To enhance the radiation capacity of the Janus-Helmholtz transducer (JHT) and achieve a broadband transmitting response, an asymmetric dual-cavity JHT is proposed and a broadband symmetric multi-cavity JHT design is introduced. Firstly, the vibration characteristics of the cylindrical liquid cavity are analyzed and two liquid cavities with different dimensions are utilized to construct the asymmetric dual-cavity JHT. The operating principles of both the typical JHT and the asymmetric dual-cavity JHT are revealed. Furthermore, an equivalent circuit model (ECM) for the asymmetric dual-cavity JHT is proposed by combining the ECMs of the Janus transducer and the liquid cavities. To validate the accuracy and generality of the ECM for the asymmetric dual-cavity JHT, four JHTs are fabricated and tested, and the finite element method (FEM) is also employed to predict their electroacoustic performance. The admittance obtained from ECM, FEM and experiment (EXPT) exhibit good agreement. Additionally, the radial transmitting voltage response (rTVR) calculated by FEM aligns well with the experimental results. Experimental results demonstrate that the asymmetric dual-cavity JHT, compared to its typical counterpart of the same dimensions, exhibits a significantly increased rTVR within the low-frequency band. Moreover, the directivity of the typical JHT and the asymmetric dual-cavity JHT are compared by FEM and the causes of radial response fluctuations in the asymmetric dual-cavity JHT are analyzed. Finally, a symmetric multi-cavity JHT with a lower resonant frequency and a wider operating bandwidth is designed through FEM, verifying the effectiveness of the multi-mode coupling design principle. The ECM for the dual-cavity JHT offers valuable theoretical support for optimizing JHT designs and the symmetric multi-cavity JHT design serves as inspirations for modifying resonant frequency, enhancing emission capability and advancing operating bandwidth of the JHTs.

Stacked subwavelength grating with high transmission

We propose a stacked subwavelength grating scheme generated multi-mode coupling that is continuously tunable in the visible range with high transmittance. This scheme uses BK7 glass as the substrate, onto which a layer of polydimethylsiloxane (PDMS) thin film is added. Each layer of the stacked grating is composed of different materials, from top to bottom are Ag-MgF2-BK7-Ag. By coupling different propagation modes generated by different grating layers, various transmission spectra throughout the entire visible range can be achieved. This scheme can not only allow the tuning range of the resonant peak cover the entire visible, but also bring extremely high transmittance, accompanied by sidebands below 10%, and the maximum peak transmittance can exceed 98%. Based on the mode matching method, this article has analyzed the magnetic field distribution in the entire structure space and the diffraction efficiency of all levels of diffraction waves. Our findings have potential applications in multispectral image sensors.

Optimization Control of Multi-Mode Coupling All-Wheel Drive System for Hybrid Vehicle

The all-wheel drive (AWD) hybrid system is a research focus on high-performance new energy vehicles that can meet the demands of dynamic performance and passing ability. Simultaneous optimization of the power and economy of hybrid vehicles becomes an issue. A unique multi-mode coupling (MMC) AWD hybrid system is presented to realize the distributed and centralized driving of the front and rear axles to achieve vectored distribution and full utilization of the system power between the axles of vehicles. Based on the parameters of the benchmarking model of a hybrid vehicle, the best model-predictive control-based energy management strategy is proposed. First, the drive system model was built after the analysis of the MMC-AWD's drive modes. Next, three fundamental strategies were established to address power distribution adjustment and battery SOC maintenance when the SOC changed, which was followed by the design of a road driving force observer. Then, the energy consumption rate in the average time domain was processed before designing the minimum fuel consumption controller based on the equivalent fuel consumption coefficient. Finally, the advantage of the MMC-AWD was confirmed by comparison with the dynamic performance and economy of the BYD Song PLUS DMI-AWD. The findings indicate that, in comparison to the comparative hybrid system at road adhesion coefficients of 0.8 and 0.6, the MMC-AWD's capacity to accelerate increases by 5.26% and 7.92%, respectively. When the road adhesion coefficient is 0.8, 0.6, and 0.4, the maximum climbing ability increases by 14.22%, 12.88%, and 4.55%, respectively. As a result, the dynamic performance is greatly enhanced, and the fuel savings rate per 100 km of mileage reaches 12.06%, which is also very economical. The proposed control strategies for the new hybrid AWD vehicle can optimize the power and economy simultaneously.

Biexcitons-plasmon coupling of Ag@Au hollow nanocube/MoS2 heterostructures based on scattering spectra.

The strong interaction between light and matter is one of the current research hotspots in the field of nanophotonics, and provides a suitable platform for fundamental physics research such as on nanolasers, high-precision sensing in biology, quantum communication and quantum computing. In this study, double Rabi splitting was achieved in a composite structure monolayer MoS2 and a single Ag@Au hollow nanocube (HNC) in room temperature mainly due to the two excitons in monolayer MoS2. Moreover, the tuning of the plasmon resonance peak was realized in the scattering spectrum by adjusting the thickness of the shell to ensure it matches the energy of the two excitons. Two distinct anticrossings are observed at both excitons resonances, and large double Rabi splittings (90 meV and 120 meV) are obtained successfully. The finite-difference time domain (FDTD) method was also used to simulate the scattering spectra of the nanostructures, and the simulation results were in good agreement with the experimental results. Additionally, the local electromagnetic field ability of the Ag@Au hollow HNC was proved to be stronger by calculating and comparing the mode volume of different nanoparticles. Our findings provides a good platform for the realization of strong multi-mode coupling and open up a new way to construct nanoscale photonic devices.

Generation of spatiotemporal dark pulse or polarization domain wall solitons in a partial multimode mode-locked fiber laser

In this paper, we have experimentally investigated different operational states of a partial multimode Er-doped spatiotemporal mode-locked (STML) fiber laser. The STML is enabled by nonlinear multimode interference (NL-MMI) effect from the partial multimode cavity structure. It is found that by adjusting the multimode polarization controller (PC) and the pump power, the STML dark pulses, bright pulses, as well as the polarization domain wall solitons can all be obtained, alternatively. The fused-tapered multimode coupler is responsible for the dark pulses generation via the enhanced modal cross-phase coupling. It is believed that the present findings can offer an important insight into the spatiotemporal dynamics of the STML solitons.

Full-scale measurements of mode coupling vibrations during super typhoons on a rectangular supertall building with limited sensors

Towards a complete and accurate assessment of the model parameters (i.e., frequency, damping ratio, and mode shape) of supertall buildings, this study proposes a new modal identification method named SCA-MBSDA based on the framework of sparse component analysis (SCA) and modified Bayesian spectral density approach (MBSDA). The feasibility and uncertainty of the SCA-MBSDA method are analyzed in an underdetermined case using a three-degree-of-freedom frame structure via numerical simulations. Through measurements from a wireless biaxial ultra-low frequency accelerometer atop the building, the variations in the first three modal parameters of a 125 m high rectangular supertall building with significant multi-mode coupling vibrations (maximum accelerations >15 cm/s2) are illustrated during typhoons Hato and Mangkhut. The results demonstrate the high effectiveness of the SCA-MBSDA method in identifying time-varying structural frequencies and mode shapes. During super typhoon conditions, the third mode of the monitored building exhibits a significant decrease in natural frequency and modal stiffness, with reduced rates of 9 % and 17 %, respectively. The averages of the first three mode directions obtained from the measurements agree well with the values obtained from the finite element model (FEM). This paper aims to provide a feasible identification method to enhance the understanding of the changes in the first three modal properties of supertall buildings during typhoons.

Integrated self-injection-locked narrow linewidth laser based on thin-film lithium niobate.

Narrow linewidth lasers have a wide range of applications in the fields of coherent optical communications, atomic clocks, and measurement. Lithium niobate material possesses excellent electro-optic and thermo-optic properties, making it an ideal photonic integration platform for a new generation. The light source is a crucial element in large-scale photonic integration. Therefore, it is essential to develop integrated narrow linewidth lasers based on low-loss LNOI. This study is based on the multimode race-track type add-drop microring resonator with multimode interferometric coupler (MMRA-MRR) of the DFB laser self-injection-locked, to achieve the narrowing of linewidth to the laser. The microring external cavity was used to narrow the linewidth of the laser to 2.5 kHz. The output power of the laser is 3.18 mW, and the side-mode suppression ratio is 60 dB. This paper presents an integrated low-noise, narrow-linewidth laser based on thin-film lithium niobate material for the communication band. This is significant for achieving all-optical device on-chip integration of lithium niobate material in the future. It has great potential for use in high-speed coherent optical communication.

Sculpting ultrastrong light-matter coupling through spatial matter structuring.

The central theme of cavity quantum electrodynamics is the coupling of a single optical mode with a single matter excitation, leading to a doublet of cavity polaritons which govern the optical properties of the coupled structure. Especially in the ultrastrong coupling regime, where the ratio of the vacuum Rabi frequency and the quasi-resonant carrier frequency of light, ΩR/ω c, approaches unity, the polariton doublet bridges a large spectral bandwidth 2ΩR, and further interactions with off-resonant light and matter modes may occur. The resulting multi-mode coupling has recently attracted attention owing to the additional degrees of freedom for designing light-matter coupled resonances, despite added complexity. Here, we experimentally implement a novel strategy to sculpt ultrastrong multi-mode coupling by tailoring the spatial overlap of multiple modes of planar metallic THz resonators and the cyclotron resonances of Landau-quantized two-dimensional electrons, on subwavelength scales. We show that similarly to the selection rules of classical optics, this allows us to suppress or enhance certain coupling pathways and to control the number of light-matter coupled modes, their octave-spanning frequency spectra, and their response to magnetic tuning. This offers novel pathways for controlling dissipation, tailoring quantum light sources, nonlinearities, correlations as well as entanglement in quantum information processing.