Arbitrary Mode Research Articles

Tuned mass damper on spacecraft reaction wheel assembly

Considering the wide frequency range and time-varying characteristics of reaction wheel assembly (RWA) micro-vibrations, an embedded tuned mass damper (TMD) was proposed herein to reduce the influence of the RWA micro-vibration effect on spacecraft. First, dynamics model of the RWA and a mechanical model of the angular contact ball bearing were constructed, and the time-varying characteristics of the RWA were theoretically analyzed. Based on single- and multiple-degree-of-freedom vibration absorption dynamics models, it was shown that the TMD could be applied to the vibration suppression of the RWA’s multi-modal and time-varying state by changing the design parameters of the TMD. Based on the RWA single-degree-of-freedom equivalent dynamics model, the effects of the TMD natural frequency and damping on the displacement amplitude ratio of the RWA were analyzed, and the sensitivities of the RWA resonance peak amplitude and resonance frequency to the two parameters were analyzed by the Sobol sensitivity analysis method. Then, according to the analysis results, the structural design of the TMD in the RWA was guided, and a test platform was built to obtain the RWA micro-vibration data. Finally, a normalized amplitude-frequency response identification algorithm was used to eliminate the effects of non-linearities in the experimental data and to identify the RWA dynamics in a time-varying state, thus obtaining the RWA amplitude–frequency response curve and verifying the results of the theoretical analysis. Theoretical and experimental data showed that the addition of a TMD structure with variable damping and stiffness within the RWA allowed for micro-vibration suppression for arbitrary modes and improved the RWA vibration characteristics. This could provide convenience for different specifications of RWA vibration suppression as well as reference for further research on the effective application of TMDs in RWAs.

Demonstration of a photonic router via quantum walks

Motivated by the need for quantum computers to communicate between multiple, well separated qubits, we introduce the task of routing the quantum state from one input mode to a superposition of several output modes coherently. We report an experimental demonstration of a deterministic photonic routing protocol applied to an entangled state. We show in a quantum walk architecture, quantum networks perfectly route entangled states from an initial input mode to an arbitrary output mode coherently and deterministically. Our results demonstrate the key principle of a perfect router, opening a route toward data routing and transferring for quantum computing systems. The routing algorithm in our work can be applied to a wide range of physical systems, which provides a way for effective design of efficient routing protocols on practical quantum networks.

Tailoring Large Asymmetric Laguerre–Gaussian Beam Array Using Computer-Generated Holography

Laguerre–Gaussian beams are structured light beams with a donut-shaped symmetric intensity profile and a helical phase profile. The beam profile is defined by a quantized parameter known as the mode number which extends to infinity. The availability of unbounded modes makes these beams a promising candidate for next-generation optical computing, and optical communication technologies. The symmetric intensity profile of a Laguerre–Gaussian beam can be made asymmetric through certain techniques and these beams are known by the term ‘asymmetric Laguerre–Gaussian beams’. Here, the asymmetricity adds another degree of freedom to the beam (apart from its mode number) which helps in encoding more information compared to a symmetric beam. However, in order to harness the benefits of all the available degrees of freedom, it is required to generate a large number of such beams in a multiplexed fashion. Here, we report the generation of such a large array of asymmetric Laguerre–Gaussian beams for the first time. Computer-generated holography and spatial multiplexing techniques were employed to generate a large array comprising of 12 × 16 = 192 asymmetric Laguerre–Gaussian beams with an arbitrary mode index and asymmetricity.

Aerodynamic Modeling and Simulation of Multi-Lifting Surfaces Based on the Unsteady Vortex Lattice Method

Using the unsteady vortex lattice method based on the potential flow theory, a rapid modeling approach is developed for the aerodynamic computation of multi-lifting surfaces. Multiple lifting surfaces with different geometric parameters and grid divisions can be quickly integrated and meshed with the object-oriented data structure. The physical influence between different lifting surfaces was modeled, and the wake–surface interaction was also considered by using different built-in vortex core models. The trajectory data were used to replace the pre-calculated downwash superposition for boundary condition integration, and the instantaneous boundary condition was generated directly from the kinematic states and mesh messages of the model concerned. Considering the direct coupling effect between aerodynamics and rigid body dynamics, the function for free flight was built for medium-fidelity dynamic simulations and aerodynamic data identifications. The proposed high-efficiency modeling and simulation process can be easily applied to models with any number of different lifting surfaces and arbitrary motion modes.

Complex Eigenvalue Analysis of Multibody Problems via Sparsity-Preserving Krylov–Schur Iterations

In this work, we discuss the numerical challenges involved in the computation of the complex eigenvalues of damped multi-flexible-body problems. Aiming at the highest generality, the candidate method must be able to deal with arbitrary rigid body modes (free–free mechanisms), arbitrary algebraic constraints, and must be able to exploit the sparsity pattern of Jacobians of large systems. We propose a custom implementation of the Krylov–Schur method, proving its robustness and its accuracy in a variety of different complex test cases.

High-dimensional spatial mode sorting and optical circuit design using multi-plane light conversion

Multi-plane light converters (MPLCs) are an emerging class of optical devices capable of converting a set of input spatial light modes to a new target set of output modes. This operation represents a linear optical transformation—a much sought after capability in photonics. MPLCs have potential applications in both the classical and quantum optics domains, in fields ranging from optical communications to optical computing and imaging. They consist of a series of diffractive optical elements (the “planes”), typically separated by a free space. The phase delays imparted by each plane are determined by the process of inverse-design, most often using an adjoint algorithm known as the wavefront matching method (WMM), which optimizes the correlation between the target and actual MPLC outputs. In this work, we investigate high mode capacity MPLCs to create arbitrary spatial mode sorters and linear optical circuits. We focus on designs possessing low numbers of phase planes to render these MPLCs experimentally feasible. To best control light in this scenario, we develop a new inverse-design algorithm, based on gradient ascent with a specifically tailored objective function, and show how, in the low-plane limit, it converges to MPLC designs with a substantially lower modal cross-talk and higher fidelity than those achievable using the WMM. We experimentally demonstrate several prototype few-plane high-dimensional spatial mode sorters, operating on up to 55 modes, capable of sorting photons based on their Zernike mode or orbital angular momentum state, or an arbitrarily randomized spatial mode basis. We discuss the advantages and drawbacks of these proof-of-principle prototypes and describe future improvements. Our work points to a bright future for high-dimensional MPLC-based technologies.

Efficient diffraction control using a tunable active-Raman gain medium

We present a scheme to create an all-optical tunable and lossless waveguide using a controllable coherent Raman process in an atomic rubidium vapor in an $\mathcal{N}$-type configuration. We employ a Gaussian Raman field and a Laguerre-Gaussian control field to imprint a high-contrast tunable waveguidelike feature inside the atomic medium. We numerically demonstrate that such a waveguide is able to guide arbitrary modes of a weak probe beam to several Rayleigh lengths without diffraction and absorption. Our results on an all-optical waveguide-based scheme may have potential applications in lossless image processing, high-contrast biomedical imaging, and image metrology.

Adaptive mesh refinement for finite element analysis of elastic buckling disturbance of circularly curved beams due to multiple micro-cracks damage

PurposeThis study aimed to overcome the challenging issues involved in providing high-precision eigensolutions. The accurate prediction of the buckling load bearing capacity under different crack damage locations, sizes and numbers, and analysing the influence mechanism of crack damage on buckling instability have become the needs of theoretical research and engineering practice. Accordingly, a finite element method was developed and applied to solve the elastic buckling load and buckling mode of curved beams with crack damage. However, the accuracy of the solution depends on the quality of mesh, and the solution inevitably introduces errors due to mesh. Therefore, the adaptive mesh refinement method can effectively optimise the mesh distribution and obtain high-precision solutions.Design/methodology/approachFor the elastic buckling of circular curved beams with cracks, the section damage defect analogy scheme of a circular arc curved beam crack was established to simulate the crack size (depth), position and number. The h-version finite element mesh adaptive analysis method of the variable section Euler–Bernoulli beam was introduced to solve the elastic buckling problem of circular arc curved beams with crack damage. The optimised mesh and high-precision buckling load and buckling mode solutions satisfying the preset error tolerance were obtained.FindingsThe results of testing typical examples show that (1) the established section damage defect analogy scheme of circular arc curved beam crack can effectively realise the simulation of crack size (depth), position and number. The solution strictly satisfies the preset error tolerance; (2) the non-uniform mesh refinement in the algorithm can be adapted to solve the arbitrary order frequencies and modes of cracked cylindrical shells under the conditions of different ring wave numbers, crack positions and crack depths; and (3) the change in the buckling mode caused by crack damage is applicable to the study of elastic buckling under various curved beam angles and crack damage distribution conditions.Originality/valueThis study can provide a novel strategy for the adaptive mesh refinement for finite element analysis of elastic buckling of circular arc curved beams with crack damage. The adaptive mesh refinement method established in this study is fundamentally different from the conventional finite element method which employs the user experience to densify the meshes near the crack. It can automatically and flexibly generate a set of optimised local meshes by iteratively dividing the fine mesh near the crack, which can ensure the high accuracy of the buckling loads and modes. The micro-crack in curved beams is also characterised by weakening the cross-sectional stiffness to realise the characterisation of locations, depths and distributions of multiple crack damage, which can effectively analyse the disturbance behaviour of different forms of micro-cracks on the dynamic behaviour of beams.

Creation of vector Bessel beams with arbitrary polarization modes using mode extraction principle

According to the current research on polarization generation methods, it is difficult to create multi-mode vector Bessel beams in free space by extracting arbitrary polarization modes from a single beam. This is due to the fact that the polarization and phase distributions between multiple polarization modes can interfere with each other. In this paper, the mode extraction principle is combined with the optical pen technique to extract arbitrary polarization modes from a single Bessel beam, and the number, position and phase of Bessel beams can be arbitrarily regulated to achieve the multi-mode coexistence of vector Bessel beams in free space. The experimental results are consistent with the theoretical analysis. This work is not only important for the in-depth study of vector Bessel beams, but also will facilitate the development of optical manipulation, optical communication, microscopic imaging and other applications.

SiFu: A Generic and Robust Multimodal Signal Fusion Platform for Pervasive Localization

We consider pervasive localization for a roaming user who may sample widely varying signal modes (GPS, WiFi, geomagnetism, Bluetooth low energy, etc.) and values over time and space. Previous works can only apply to specific (two or three) modes and environment, and cannot accommodate arbitrary signal modes and environmental changes due to signal noise, device heterogeneity, phone carriage states, etc. We propose SiFu, a simple, accurate, and generic multimodal signal fusion platform robust against environmental deviation from its design point. As a generic framework, SiFu treats a single-modal localization algorithm as a black box to embrace any existing, emerging or future signals with only incremental training. It employs Bayesian deep learning and data augmentation to mitigate the location bias of the single-modal localization algorithm and run-time deviation from the training data, respectively. Using a unified multimodal likelihood formulation and particle filter, it fuses with inertial sensor measurements for localization. We conduct extensive experiments in different venues (campus, mall, and subway station), and show that SiFu achieves significantly higher localization accuracy as compared to state-of-the-art (cutting the error by more than 20%). It is also robust against environmental variations (reducing error by 30%), even when the signal values deviate greatly from their original design settings.

A Generalized Geodesic Distance-Based Approach for Analysis of SAR Observations Across Polarimetric Modes

Present and future sensors are diversifying from traditional quad polarimetric mode of synthetic aperture radar acquisition. Thus, an approach that is interpretative in nature and applicable across polarimetric modes is required. In this context, the geodesic distance (GD)-based approach within the polarimetric synthetic aperture radar (PolSAR) literature is seen as an eigenvalue-decomposition free approach to interpret and analyze quad PolSAR data. This approach is highly adaptive toward applications due to its ability to compare the SAR observation with a known scatterer/model, or with another SAR observation in general providing a means for direct interpretation. In this work, we show that the GD (originally defined for the quad polarization mode) is generalizable across any arbitrary SAR polarimetric mode while retaining its simple form for ready computation. We show that the GD-based approach provides level ground for comparison of different polarimetric modes given a fixed application. We demonstrate it using change detection as the chosen application. In addition, we show how the behavior of the three roll-invariant GD-based parameters change under different polarimetric modes (e.g., quad, dual, and compact polarization modes). We also discuss how the GD-based approach can also be adapted to ground range detected (GRD) product data, which is presently available from Sentinel-1 and widely used in many applications. However, in this case, we show that only one of the three GD-derived parameters can be defined. We believe this work will make the GD-based approach important for present and future PolSAR applications cutting across sensors and its available polarimetric modes.

Orbital angular momentum mode sorting by wavefront shaping with customizable optical phase conjugation through a diffuser

Light field control through a diffuser using feedback wavefront shaping (WS) is an emerging method for sorting in orbital angular momentum (OAM) multiplexed communications. However, the feedback iterative optimization of the wavefront shaper converges slowly, reducing the real-time capability. Herein, we developed a WS scheme using a diffuser with customizable optical phase conjugation (COPC) for arbitrary OAM light control and mode sorting without iteration. The numerical and experimental results showed that the multiplexed OAM mode can be sorted into predefined spatial positions. Moreover, we found that the OAM mode with a larger topological charge |l| has stronger focusing, i.e., higher transmittance through the diffuser. Furthermore, we demonstrated that two, four, six, and eight modes can be sorted beyond 0.99, 0.93, 0.87 and 0.79 detection probabilities in the experiment.

Mode-insensitive 3-dB power splitter based on multimode-interference coupler

We proposed a broadband 3-dB power splitter based on multimode-interference coupler formed by polymer waveguide, which is insensitive to the arbitrary input modes, and demonstrated the operation functions of the design in the experiment. The design shows a mode-insensitive 3-dB power splitting for the E11, E21 and E12 modes with an imbalance power less than 0.11, 0.13 and 0.03 dB, respectively, over a 100 nm bandwidth that ranges from 1520 to 1620 nm. Our presented mode-insensitive 3-dB power splitter could find applications in mode (de)multiplexing systems where ultra-broadband power splitting is required.

QED vacuum nonlinearity in Laguerre-Gauss beams

We investigate in detail the stimulated photon emission in pulse-shaped Laguerre-Gauss beams of arbitrary mode decomposition within the framework of Euler-Heisenberg effective theory. We elaborate on the analytic structure of the photon emission amplitude and identify its dominant and subdominant parts by analyzing each signature's phase scaling. We identify three distinct nonlinear signatures: the orbital angular momentum flip ($\ensuremath{\ell}:\text{ }\text{ }1\ensuremath{\rightarrow}\ensuremath{-}1$), higher harmonic generation ($\ensuremath{\ell}:\text{ }\text{ }1\ensuremath{\rightarrow}2$), and harmonic reduction ($\ensuremath{\ell}:\text{ }\text{ }1\ensuremath{\rightarrow}0$). We estimate the signal photon yield for each signature under various pulse collision scenarios we explain in detail. We also outline a prospective experimental setup that may probe these signatures.

Efficient transfer of spatial intensity and phase information of arbitrary modes via four-wave mixing in an atomic vapor

We propose a scheme to transfer the spatial intensity as well as phase information encoded initially in the spatial profile of a weak probe field onto a newly generated Stokes field in a nonlinear process of four-wave mixing (FWM). The FWM process is explored in a gaseous medium consisting of atoms modeled as a three-level system in the $\mathrm{\ensuremath{\Lambda}}$ configuration. We found that different orders of Hermite-Gaussian and Laguerre-Gaussian modes carried by a probe beam are effectively transferred to a Stokes beam. Interestingly, the transferred intensity of the Stokes beam is a clone of the probe beam, whereas the phase profile is conjugate to the probe. The phase distribution of the transmitted modes at the exit of the medium is explored by superimposing them on a copropagating plane wave. Moreover, the parametric amplification due to the nonlinear process of FWM prevents any information loss due to linear absorption and permits us to work at high optical depths. We found a structural similarity between transferred images of about $99%$, which provides clear evidence for the successful transfer of information in the FWM process.

Variable Aperture Technique for Measuring Mode Field Diameters Corresponding to Laguerre Gaussian Spot Size of Higher-Order Modes of Few-Mode Fibers

The mode field diameter (MFD) is an essential parameter for understanding the transmission characteristics of optical fibers. A variable aperture (VA) technique is a standard test method for measuring the MFD of single-mode fibers. Unfortunately, the conventional one cannot measure the MFDs of some higher-order modes correctly because its measurement procedure is standardized for measuring the MFD of the fundamental mode. The conventional VA technique aligns the position of the optical fiber through a peak intensity search on the premise that the fundamental mode, whose intensity is maximum at the beam center, is measured. How to align the position of the optical fiber when measuring the MFD of higher-order modes has not yet been investigated. In this paper, we describe the principle and formulas based on the VA technique for measuring the MFD of a given higher-order mode in few-mode fibers (FMFs). Then, we propose a novel procedure for measuring the MFDs of FMFs. The test apparatus of our technique is almost the same as that of the conventional VA technique except for the use of a mode selective coupler. One can measure the MFDs of arbitrary modes in FMFs correctly by adjusting the position of the fiber under test using the fundamental mode before starting the measurement. Proof-of-principle experiments were performed for three kinds of FMFs, and the experimental results showed that our procedure is useful for characterizing the MFD of each mode.

Reconfigurable reflective multifunction OAM metasurface based on spin-decoupling.

This Letter develops a spin-decoupled reconfigurable reflective orbital angular momentum (OAM) metasurface (MTS). The reconfigurability is realized by switching the feed among left-hand circular polarization (LHCP), right-hand circular polarization (RHCP), and linear polarization (LP) incidences, and the reconfigurable design principle is provided. This Letter also proposes a design method for the desired energy ratio between the co-polarized and cross-polarized beams. Compared with published multifunction MTSs, the designed MTSs have the following advantages: multi-polarizations, arbitrary beam numbers and modes, composite waveform (pencil and OAM beams), high aperture efficiency (21.1%, 14.6%, 6.63% for RHCP, LP, and LHCP incidences, respectively), high purity (above 92.41%), required energy distribution ratio, and reconfigurability. The MTSs have potential prospects in high-capacity wireless communications.

Dispersive Resonance Modulation Based on the Mode-Coupling Effect in a Capacitive Micromechanical Resonator

This paper presents a theoretical and experimental investigation into the electrostatic coupling mechanism between different nonlinear modes inside a single resonator. Nonlinear intermodal coupling allows an arbitrary mode to be used as a modulator for the resonance of the coupled mode, presenting an efficient method to tune the frequency of a specific vibration mode. Here, a capacitive micromechanical resonator is developed, in which different modes exhibit different nonlinear characteristics. Inside this resonator, interactions between different nonlinear modes induced by electrostatic fields are observed and accurately modeled. It demonstrates that resonance modulation control can be achieved by activating the coupled modes based on the dispersive parametric coupling effect. Meanwhile, the resonance modulation is jointly determined by coupled modes, providing a theoretical basis and approach for modal manipulation technology. The dispersive coupling between intrinsic modes enables the probe resonance to be tuned by nearly 100 times its bandwidth, and its range and polarity can also be controlled by selecting the resonance of the pump mode. It is proven that resonance modulation control induced by the modal coupling effect can efficiently tune the resonator's resonance frequency over a wide range, which presents a promising voltage-frequency transduction scheme with high sensitivity and low noise for the precision instrument. Its pull range exhibits a great potential of more than 20% as a voltage-controlled oscillator and can be customized to satisfy different requirements, paving the way toward advanced mechanics.

Controlled generation of mode-switchable nanosecond pulsed vector vortex beams from a Q-switched fiber laser.

We reported and demonstrated a ring Q-switched Ytterbium-doped fiber laser that can generate mode-switchable nanosecond pulsed vector vortex beams between two different orders. In the spatial optical path of the fiber laser, several cascaded Q-plates, divided into two Q-plate groups, are applied for intracavity mode conversion between LP01 mode and vector vortex beams. In one Q-plate group, two quarter-wave plates are inserted to achieve the addition and subtraction of the order of Q-plates. By tuning the polarization state in the cavity, mode-switchable vector vortex beams (VVBs), including cylindrical vector beams (CVBs), elliptically polarized cylindrical vector beams (EPCVBs), and vortex beams, of two different orders can be generated on demand. The experimental results show that by using the group of 1st and 3rd orders Q-plates, the 2nd and 4th orders mode-switchable VVBs (vortex beams with topological charges of ±2, ±4, CVBs and EPCVBs of 2nd- and 4th-order) can be obtained from the fiber laser. The slope efficiency, pulse width, and repetition rate are 33.4%, 360 ns, and 241kHz respectively. To the best of our knowledge, this is the first time to realize the direct generation of mode-switchable VVBs on the arbitrary position of the higher-order Poincaré sphere between two different orders from a fiber laser. This work lays the foundation for the flexible generation of arbitrary modes of VVBs with multiple different orders in the laser cavity.

Multi-mode response spectrum for multi-harmonic crowd jumping loads

A major challenge in the vibration performance assessment of structures under crowd jumping loads is the lack of efficient prediction models. With the challenge in mind, this study develops a multi-mode response spectrum for multi-harmonic crowd jumping loads to predict the root mean square value of structural accelerations according to the stochastic vibration theory. The response spectrum is applicable to structures with arbitrary vibration modes, because crowd jumping loads are regarded as multi-point excitations. A random field model proposed by the author is used to derive the closed-form expression of the single-mode response induced by individual jumping loads of a single-harmonic. Furthermore, the closed-form expressions of the correlation coefficients for different load harmonics, different vibration modes, and different jumping persons are established based on the random field model. The performance of the response spectrum is evaluated for two floors, and the results indicate the feasibility of the proposed approach to predicting structural accelerations subjected to crowd jumping loads.