Multimode System Research Articles

Ground-state cooling of multiple near-degenerate mechanical modes

We propose a general and experimentally feasible approach to realize simultaneous ground-state cooling of arbitrary number of near-degenerate, or even fully degenerate mechanical modes, overcoming the limit imposed by the formation of mechanical dark modes. Multiple optical modes are employed to provide different dissipation channels that prevent complete destructive interference of the cooling pathway, and thus eliminating the dark modes. The cooling rate and limit are explicitly specified, in which the distinguishability of the optical modes to the mechanical modes is found to be critical for an efficient cooling process. In a realistic multi-mode optomechanical system, ground-state cooling of all mechanical modes is demonstrated by sequentially introducing optical drives, proving the feasibility and scalability of the proposed scheme. The work may provide new insights in preparing and manipulating multiple quantum states in macroscopic systems.

Controllable Phononic Low-Pass Filter via Optomechanical Interactions

We present an experimental demonstration of an optically controllable phononic low-pass filter in a multimode optomechanical system. By coupling two spatially separated nanomechanical resonators via optomechanical interactions, the phononic signal below a cutoff frequency can be transferred between mechanical resonators, while the signal above the cutoff frequency is attenuated, which resembles an electronic low-pass filter. Moreover, the cutoff frequency is controllable by tuning the optomechanical interaction via the intracavity field. Our results provide an essential element in phononic circuits and have potential applications for information processing in hybrid quantum systems.

Hybrid Magnonics for Short-Wavelength Spin Waves Facilitated by a Magnetic Heterostructure

Recent research on hybrid magnonics has been restricted by the long magnon wavelengths of the ferromagnetic resonance modes. We present an experiment on the hybridization of 250-nm-wavelength magnons with microwave photons in a multimode magnonic system consisting of a planar cavity and a magnetic bilayer. The coupling between magnon modes in the two magnetic layers, i.e., the uniform mode in Permalloy and the perpendicular standing spin waves (PSSWs) in yttrium iron garnet, serves as an effective means for exciting short-wavelength PSSWs, which is further hybridized with the photon mode of the microwave resonator. The demonstrated magnon-photon coupling approaches the superstrong coupling regime, and can even be achieved near zero bias field.

Spatiotemporal self-mode-locked operation in a compact partial multimode Er-doped fiber laser.

We report spatiotemporal self-mode-locked operation at 1.55 µm with a low pump threshold of 32 mW in a compact partial multimode fiber laser system. Spatial filtering and the saturable absorber, both of which originate from the multimode interference (linear or nonlinear) of the single mode-multimode structure in this hybrid configuration, are well suited to the spatiotemporal self-mode-locked operation. Not only stable multimode conventional solitons with different spectral bandwidths but also a multimode soliton molecule complex with different structural bound-state patterns are obtained. It is found that the spatiotemporal evolution of the multimode solitons is dependent on many factors, such as the operating state, the involved frequency component, and the interaction between solitons. Furthermore, an unstable spatiotemporal mode-locked (STML) state where the beam profiles of the solitons change spontaneously is also observed for a specific multimode fiber state and pump power.

Research on mode-coupled multi-mode Fiber mode-division in multiplexing transmission system

The mode coupling and random loss between different modes have important effects on the reliability of the multimode fiber-based mode division multiplexing transmission system. Using the VPI optical communication simulation platform, a short-distance analog-division multiplexing transmission system based on multimode fiber was designed and built. By setting the relevant parameters of mode coupling and random loss caused by bending, the quality of the eye diagram of the received signal is analyzed by the photoelectric signal analyzer at the receiving end. The experimental results show that the mode coupling has great influence on the anti-noise performance and anti-inter-symbol interference performance of the multimode fiber-based transmission system, and the random loss has great influence on the anti-noise performance of the system, this effect is more obvious in high-order linear polarization mode fiber.

Conditions for experimental detection of one-way quantum steering in a three-mode optomechanical system

Conditions for experimental detection of asymmetric one-way quantum steering in a three-mode optomechanical system are examined. We consider cases of collective steering in which two modes collectively interact with the third mode, and the case of separate modes steering in which two mutually independent modes interact with the third mode. We find that the occurrence of both collective and separate modes quantum steering results not from an asymmetry between thermal noise of the modes, as it has been realized in linear optics systems, but from an asymmetry between the damping rates of the modes. We show the requirement that the modes are damped with different rates to be the necessary and sufficient condition for collective steering. In the case of separate modes, we find that apart from unequal damping rates, an additional condition is required that the modes are coupled to the third mode with unequal strengths. Thus, the generation of quantum steering between separate modes is more restrictive to the parameters than the collective steering. Determination of conditions for experimental detection of one-way steering in multi-mode system could give a new stimulus to develop secure directional communication networks.

Multilayer structures and resilience evaluation for multimode regional rail transit system

The integrated travel demand has promoted the interconnection of multimode rail transit. As different rail transit systems are separately modeled, current network and resilience evaluation methods are limited in addressing interconnected characteristics and various travel demands. In this study, a multilayer network was constructed to validly understand the interconnected characteristics of the multimode regional rail transit system (MRRTS). A weighted multilayer regional rail transit network (W-MRRTN) was presented to describe the travel demands and choices from an overall system perspective. Based on the W-MRRTN combined with topological and operational features, a novel performance indicator was proposed, explicitly considered travel delays and rerouting. Furthermore, a specific definition, performance-based metric, and simulation approach for resilience evaluation that characterized the absorptive, adaptive, and restorative capacities, was proposed. The consequences of accumulative and rerouted passengers were expressly considered to quantify the time-dependent resilience under different disruptions. The proposed framework was applied to MRRTS in Chongqing metropolitan area, China. The results identify the stations with the highest impact on network connectivity and passenger flow, thereby proving the assortative and heterogeneous ability of the network. The comprehensive performance indicator evaluates the system more accurately than that using a single indicator. Moreover, the system under the disruption of 10, 20, and 35 min have no adaptive capacity, indicating that MRRTN is non-resilient. The development of adaptive capacity can improve system resilience. In addition, attention should be paid to the transfer stations located near the disrupted stations. The methods and results presented in this study can be adopted as a support multimode system by transport planners, managers, and policymakers.

Nonlinear quantum behavior of ultrashort-pulse optical parametric oscillators

The quantum features of ultrashort-pulse optical parametric oscillators (OPOs) are investigated theoretically in the nonlinear regime near and above threshold. Viewing the pulsed OPO as a multimode open quantum system, we rigorously derive a general input-output model that features nonlinear coupling among many cavity (i.e., system) signal modes and a broadband single-pass (i.e., reservoir) pump field. Under appropriate assumptions, our model produces a Lindblad master equation with multimode nonlinear Lindblad operators describing two-photon dissipation and a multimode four-wave-mixing Hamiltonian describing a broadband, dispersive optical cascade, which we show is required to preserve causality. To simplify the multimode complexity of the model, we employ a supermode decomposition to perform numerical simulations in the regime where the pulsed supermodes experience strong single-photon nonlinearity. We find that the quantum nonlinear dynamics induces pump depletion as well as corrections to the below-threshold squeezing spectrum predicted by linearized models. We also observe the formation of non-Gaussian states with Wigner-function negativity and show that the multimode interactions with the pump, both dissipative and dispersive, can act as effective decoherence channels. Finally, we briefly discuss some experimental considerations for potentially observing such quantum nonlinear phenomena with ultrashort-pulse OPOs on nonlinear nanophotonic platforms.

Steady-state dynamic analysis of a nonlinear fluidic soft actuator

The internal channel networks embedded within a soft structure can be a fruitful mechanism to create and activate actuators in the research fields of soft robotics. The deformation of the supporting elastic structure from the pressurized viscous fluid into the channels needs an accurate investigation. In this paper, accurate modeling and dynamic analysis of this nonlinear soft actuator is our goal. In this modeling, the soft actuator is considered the Euler–Bernoulli beam with large deflection and nonlinear strain. After implementing Hamilton’s principle, the assumed mode method is used to achieve the mathematical model in terms of the multi-mode system that is more similar to the flexible nature of the actuation system. Steady-state dynamics is investigated by a combination of the complex averaging method with arc-length continuation. The accuracy of the proposed modeling is validated by comparing simulation results to those obtained with a nonlinear finite element method and numerical method. It shows that only one-third of the degree-of-freedoms used for the finite element method are sufficient to obtain equivalent converged solutions with the proposed model. The effect of nonlinear strain and multi-mode consideration in the analysis of the proposed modeling is investigated. It is advantageous to analyze the system performance by looking into the geometrical parameters and fluid properties.

An evidential reasoning-based fault detection method for multi-mode system

A multi-mode system (MMS) is often switched among different modes which can experience great state changes. Compared with the single-mode system, fault detection for MMS is more challenging due to the diversity of states. The existing fault detection methods for MMS are mainly the data-driven based which cannot effectively combine expert knowledge with observation data. In this paper, a new multi-mode identification framework is constructed based on the evidential reasoning approach with interval reference values (ER-IRV), which can integrate thresholds of different modes. In this framework, a two-stage fault detection method is proposed. In the off-line stage, a multi-threshold optimization algorithm is developed by aggregating historical data recursively using the ER-IRV. Based on the optimized thresholds, transition processes are modeled using the membership degree of standard transitional data to steady modes. In the on-line stage, steady modes are identified by aggregating multiple attributes, and transition processes can be identified by analyzing the membership degree variation characteristics. Finally, fault detection can be realized by univariate threshold detection method and transitional slope detection method respectively. The implementation procedure of the methodology is given by a numerical example. The practical application effect is verified by a fault detection experiment on satellite turntable system.

Dynamic performance of a multi-mode operation CO2-based system combining cooling and power generation

The CO2-based combined cooling and power generation system (CCP) is considered as a promising solution for waste heat recovery due to its multiple energy outputs, environmental protection, and compactness. In this work, for waste heat recovery in refrigerated trucks, a dynamic simulation model of a multi-mode CO2-based CCP system is established in Matlab/Simulink and the experimental data verifies the dynamic simulation model well. The effect of engine heat source, condenser cooling water, and operation mode on the dynamic behavior of the CCP system is analyzed. The results show that the power output will slightly improve when switching from integrated refrigeration and power mode to full power mode. In addition, exhaust gas temperature, flue gas flow, and condenser cooling water temperature are the main disturbance factors affecting the operation of the CCP system. Moreover, in the case of sufficient condenser cooling water, the correlation between the power sub-cycle and the refrigeration sub-cycle of the CO2-based CCP system is weak, so the two sub-cycles can be controlled independently. The preliminary results presented in this paper will be helpful for the future design and the development of control strategies for the CO2-based CCP system.

Few-photon transport via a multimode nonlinear cavity: Theory and applications

Few-photon transport via waveguide-coupled local quantum systems has attracted extensive theoretical and experimental studies. Most of the study has focused on atomic or atomic-like local quantum systems due to their strong light-matter interaction useful for quantum applications. Here, we study few-photon transport via a waveguide-coupled multimode optical cavity with second-order bulk nonlinearity. We develop a Feynman diagram approach and compute the scattering matrix of the one- and two-photon transport. Based on the calculated scattering matrix, we show highly nonclassical photonic effects, including photon blockade and $\pi-$conditional phase shift, are achievable in the waveguide-coupled multimode optical cavity system via quantum interference and linear response engineering. Our results might lead to significant applications of quantum photonic circuits in all-optical quantum information processing and quantum network protocols.

Development and user experience of an innovative multi-mode stroke rehabilitation system for the arm and hand for patients with stroke

Many individuals with stroke experience upper-limb motor deficits, and a recent trend is to develop novel devices for enhancing their motor function. This study aimed to develop a new upper-limb rehabilitation system with the integration of two rehabilitation therapies into one system, digital mirror therapy (MT) and action observation therapy (AOT), and to test the usability of this system. In the part I study, the new system was designed to operate in multiple training modes of digital MT (i.e., unilateral and bilateral modes) and AOT (i.e., pre-recorded and self-recorded videos) with self-developed software. In the part II study, 4 certified occupational therapists and 10 stroke patients were recruited for evaluating usability. The System Usability Scale (SUS) (maximum score = 100) and a self-designed questionnaire (maximum score = 50) were used. The mean scores of the SUS were 79.38 and 80.00, and those of the self-designed questionnaire were 41.00 and 42.80, respectively, for the therapists and patients after using this system, which indicated good usability and user experiences. This novel upper-limb rehabilitation system with good usability might be further used to increase the delivery of two emerging rehabilitation therapies, digital AOT and MT, to individuals with stroke.

Safety lifetime analysis method for multi-mode time-dependent structural system

It is important to determine the safety lifetime of Multi-mode Time-Dependent Structural System (MTDSS). However, there is still a lack of corresponding analysis methods. Therefore, this paper establishes MTDSS safety lifetime model firstly, and then proposes a Kriging surrogate model based method to estimate safety lifetime. The first step of proposed method is to construct the Kriging model of MTDSS performance function by using extremum learning function. By identifying possible extremum mode of MTDSS, the performance function of MTDSS can be equivalently transformed into the one of Single-mode Time-Dependent Structure (STDS). The second step is to use the Advanced First Failure Instant Learning Function (AFFILF) to train the Kriging model constructed in the first step, so that the convergent Kriging model can identify the possible First Failure Instant (FFI) of STDS. Then safety lifetime can be searched quickly by dichotomy search. By using AFFILF, the minimum instant that the state is not accurately identified by the current Kriging model is selected as the training point, which avoids the unnecessary calculation which may be introduced into the existing First Failure Instant Learning Function (FFILF). In addition, the Candidate Sample Pool (CSP) reduction strategy is also adopted. By adaptively deleting the random candidate sample points whose FFI have been accurately identified by the current Kriging model, the training efficiency is further improved. Three cases show that the proposed method is accurate and efficient.

Joint pre‐ and post‐equalization using optical multi‐level signaling

A joint pre- and post-equalization scheme is proposed for an optical intensity modulation and direct detection (IM/DD) system. At the transmitter, a linear feed-forward pre-equalizer with just two, three, or four filter taps is suggested to limit the transmitter's complexity and to allow the use of multi-level modulation. Finally, this concept is combined with a zero-forcing post-equalizer at the receiver. By utilizing numerical optimization to design the multi-level signals, the intersymbol-interference originating from the channel is mitigated pre-equalizer taps, a reduction of 3 % in received power compared to a conventional zero-forcing design is achieved. The equalization scheme is tailored for an optical IM/DD system. Therefore, the specific power constraints of such a setup are taken into account in the equalizer design process. In contrast to existing research, the approach is tested for a multi-mode fiber system, which is affected by increased inter-symbol interference due to modal dispersion. The simulation results show that by shifting a small portion of the equalization complexity to the transmitter side, the required optical power to reach a bit-error rate of 10 − 3 $10^{-3}$ is reduced by 7.3% for zero-forcing and 6.8% for minimum mean square error post-equalizers. the noise increase by the post-equalizer is reduced by 6.9 % when including the pre-equalizer with just two filter taps. Compared to an equalization scheme that solely relies on a zero-forcing post-equalizer, the suggested joint pre- and post-equalization scheme is able to improve the bit-error rate performance by an average of 7.15 %. A testbed experiment with a 250 m multi-mode fiber channel and a data rate of 2.5 Gbps operating at 1550 nm confirms these simulation results.

Exploring changes in individuals travel behaviour after bus Rapid Transit implementation in Dar es Salaam

The use of Informal Public Transport (IPT; i.e., minibuses, motorcycles, and tricycles) for activity participation in Dar es Salaam is associated with mobility difficulties, e.g., traffic congestion, unscheduled services, and lack of safety of the journey. The introduction of the Bus Rapid Transit (BRT) in May 2016 aimed at reducing mobility difficulties by improving public transport (PT) with scheduled services and fully dedicated lanes to improve access to the Central Business District. This study compares individuals' travel behaviour before and (2 years) after BRT implementation using a GPS-app to explore changes in spatial mobility demands, i.e., (new) visited places, frequency of travel, trip distances, and departure times. Short surveys were used to record the socio-demographic characteristics. Results: the use of IPT remained a necessary means of transport for low-income individuals to commute outside the BRT corridor in multiple destinations, as the use of the BRT route is spatially limited. The new BRT system had become the main option for trips conducted to fixed destinations along the corridor and within service hours. The spatial mobility patterns showed that individuals are now adding BRT to their trip chaining, enabling them to access amenities, make more trips and travel farther distances. The results provide insights for transportation planners who tend to focus mainly on BRT as the only solution for all mobility demands. Each transport system has its own spatial mobility benefits to offer. An integrated PT within a framework of a multimode system is vital for inclusive mobility.

A Multi-Mode Public Transportation System Using Vehicular to Network Architecture

The number of accidents in the campus of Suranaree University of Technology (SUT) has increased due to increasing number of personal vehicles. In this paper, we focus on the development of public transportation system using Intelligent Transportation System (ITS) along with the limitation of personal vehicles using sharing economy model. The SUT Smart Transit is utilized as a major public transportation system, while MoreSai@SUT (electric motorcycle services) is a minor public transportation system in this work. They are called Multi-Mode Transportation system as a combination. Moreover, a Vehicle to Network (V2N) is used for developing the Multi-Mode Transportation system in the campus. Due to equipping vehicles with On Board Unit (OBU) and 4G LTE modules, the real time speed and locations are transmitted to the cloud. The data is then applied in the proposed mathematical model for the estimation of Estimated Time of Arrival (ETA). In terms of vehicle classifications and counts, we deployed CCTV cameras, and the recorded videos are analyzed by using You Only Look Once (YOLO) algorithm. The simulation and measurement results of SUT Smart Transit and MoreSai@SUT before the covid-19 pandemic are discussed. Contrary to the existing researches, the proposed system is implemented in the real environment. The final results unveil the attractiveness and satisfaction of users. Also, due to the proposed system, the CO2 gas gets reduced when Multi-Mode Transportation is implemented practically in the campus.

Influence of perturbation amplitude and perturbation frequency on Fermi-Pasta-Ulam-Tsingou recurrence phenomenon

Fermi-Pasta-Ulam-Tsingou recurrence (FPUT) phenomenon refers to the property of a multimode nonlinear system returning to the initial states after complex stages of evolution. The FPUT recurrence phenomenon closely links with modulation instability (MI) by employing the perturbed continuous waves as the initial condition. When the perturbation frequency is located inside the MI spectra, then the perturbed CWs are unstable and the perturbations will grow up with evolution. This nonlinear MI evolution results in the FPUT phenomenon. In this work, we explore in detail the effects of perturbation amplitude and perturbation frequency on the FPUT recurrence phenomena numerically, which has never been studied systematically, to the best of our knowledge. Using the results of our studies, we find that the perturbation amplitude can significantly affect the FPUT phenomenon. Firstly, the number of FPUT cycles is very sensitive to the perturbation amplitude. Large (small) perturbation amplitude can result in much more (much less) FPUT cycles. Secondly, very irregular (regular) FPUT wave evolution together with the corresponding spectra evolution can be observed at relatively large (small) values of perturbation amplitude, where the unequal (equal) distances are observed between adjacent maximum wave amplitudes spatially in the background of optical fibers. In contrast, the effects of perturbation frequency on the FPUT cycles are relatively minor, and the maximum FPUT cycles are observed at perturbation frequencies around the optimal modulation frequency generating the peak MI gain. However, the perturbation frequency can drastically affect the number of high-order sidebands excited at the distances of periodic maximum wave amplitude formation. We find that larger perturbation frequency leads to much fewer high-order sidebands. According to our studies, for observing FPUT conveniently and observing more FPUT cycles, the perturbation amplitude of the input signal should be as large as possible and the perturbation frequency should be around the optimum modulation frequency. We should also emphasize that the large perturbation amplitude results in irregular FPUT patterns with unequal distances between adjacent maximum wave amplitude formations spatially in the background of optical fibers, and large perturbation frequency results in much less high-order sidebands. Our results will provide very helpful information for the FPUT observation in experiment, and should arouse the interest of the readers in nonlinear physics.

Triplet–triplet annihilation upconversion combined with afterglow phosphors for multi-dimensional anti-counterfeiting and encoding

A multi-mode luminescent system combining triplet–triplet annihilation upconversion with afterglow phosphors through energy transfer is demonstrated and applied for multi-dimensional anti-counterfeiting and encoding applications.

Reliability analysis model of time-dependent multi-mode system under fuzzy uncertainty: Applied to undercarriage structures

There lacks fuzzy reliability analysis model to assess the reliability level of time-dependent multi-mode system (T-sys) under fuzzy uncertainty, thus this paper defines T-sys failure possibility firstly to address this problem. Then fuzzy simulation is proposed for estimating the failure possibility of T-sys (T-sys-FS), in which the failure possibility estimation of T-sys is transformed into searching fuzzy design point, a failure point with the largest joint membership degree. To improve the efficiency of T-sys-FS for searching fuzzy design point, adaptive Kriging is inserted into T-sys-FS to establish a more efficient method shorten as T-sys-AK-FS. By use of the relationship between the failure state of T-sys and that of transient single mode, a new learning function is proposed in T-sys-AK-FS, on which the critical mode and critical instant may be selected for efficiently updating Kriging model of T-sys performance function. Additionally, based on the partial correct information provided by the current Kriging model and the properties of the fuzzy design point, an improved T-sys-AK-FS version (T-sys-AK-FSi) is proposed by combining the candidate sample pool reduction strategy, then the computational efficiency is enhanced further for searching the T-sys fuzzy design point. Several examples are presented to illustrate the accuracy and efficiency of the proposed methods.