Mode Interference Research Articles

Dynamic test of the continuously variable weak force by a torsion pendulum with pre-applied stress

High-precision, continuously variable weak force testing is required for high-precision drag-free control with micro-thrust of spacecrafts, which is a key technology for space gravitational wave detection programs, such as TianQin, LISA, and Taiji. The continuously variable micro-thrust range is 0.1∼100μN, and the noise is below 0.1 μNHz−1/2 from 10−4Hz to 1 Hz. The torsion pendulum is considered as the most classical weak force measurement tool. However, the large response of non-sensitive modes makes it unsuitable for dynamic weak force measurements. In this study, a dynamic test system is developed for continuously varying weak forces using a torsion pendulum. We pre-applied a stress to the torsion pendulum using a double wire structure, which can effectively reduce the interference of other modes, and used feedback control to improve the stability. The evaluation results obtained using the external continuously variable electrostatic force indicate that the measurement range of the system covers 100 μN, the response time is approximately 1.6 s, and the noise is below 0.1 μNHz−1/2 from 0.9×10−4Hz to 1.4 Hz, which can meet the requirements of the micro-thrust test in space gravitational wave detection missions.

Improved resolution in fiber bundle inline holographic microscopy using multiple illumination sources.

Recent work has shown that high-quality inline holographic microscopy images can be captured through fiber imaging bundles. Speckle patterns arising from modal interference within the bundle cores can be minimized by use of a partially-coherent optical source such as an LED delivered via a multimode fiber. This allows numerical refocusing of holograms from samples at working distances of up to approximately 1 mm from the fiber bundle before the finite coherence begins to degrade the lateral resolution. However, at short working distances the lateral resolution is limited not by coherence, but by sampling effects due to core-to-core spacing in the bundle. In this article we demonstrate that multiple shifted holograms can be combined to improve the resolution by a factor of two. The shifted holograms can be rapidly acquired by sequentially firing LEDs, which are each coupled to their own, mutually offset, illumination fiber. Following a one-time calibration, resolution-enhanced images are created in real-time at an equivalent net frame rate of up to 7.5 Hz. The resolution improvement is demonstrated quantitatively using a resolution target and qualitatively using mounted biological slides. At longer working distances, beyond 0.6 mm, the improvement is reduced as resolution becomes limited by the source spatial and temporal coherence.

Vernier-effect-based fiber microcoupler for highly sensitive liquid refractive index sensing

An orthogonal mode interferometer (OMI) is proposed and experimentally demonstrated for liquid refractive index sensing using the optical Vernier effect. The OMIs are based on weakly fiber microcouplers, which are fabricated by fusing single mode fiber and coreless fiber together. Owing to the birefringent characteristic of the hybrid coupler, the optical Vernier effect is dependent on the overlap of mode interference between the x and y polarizations. Compared to the response of the individual resonance dip, the signal demodulation of the Vernier envelope exhibits more excellent signal amplification capability. Experimental results show that the Vernier envelope of the OMI achieves a refractive index (RI) sensitivity of 22 427.03 nm/RIU near the RI of 1.33 with a magnification factor of 4.1. Moreover, with its high sensitivity, flexible design and simplified configuration, our proposed OMI based on the optical Vernier effect is well suitable for a wide range of biosensing applications.

Adaptive Interference Avoidance and Mode Selection Scheme for D2D-Enabled Small Cells in 5G-IIoT Networks

Adaptive Interference Avoidance and Mode Selection Scheme for D2D-Enabled Small Cells in 5G-IIoT Networks

Design of anti-temperature interference liquid level sensor based on π-phase-shifted LPFG near phase-matched turning points

A new, to the best of our knowledge, type of liquid level sensor with π-phase-shifted long-period fiber grating operating near the phase-matched turning point is proposed. The sensor introduces a π-phase shift at the center of the grating, which can generate three attenuation peaks due to the mode interference effect in the transmission spectrum of the sensor operating near the phase-matched turning points. According to the different liquid level and temperature sensing characteristics of three attenuation peaks, simultaneous detection of liquid level and temperature can be realized through wavelength modulation and intensity modulation detection. In this paper, the structural parameters of this liquid level sensor, such as grating period and grating length, are designed optimally based on the fiber grating coupled mode theory, and the wavelength spacing of the attenuation peaks on both sides and the intensity of the center attenuation peak are analyzed in relation to the liquid level and temperature. The simulation results show that the liquid level sensitivity is 5.58 nm/mm and −1.316dB/mm for wavelength modulation and intensity modulation, respectively, for the liquid level variation range of 0 to 18 mm; and the temperature sensitivity of wavelength modulation and intensity modulation is −0.139nm/∘C and 0.171 dB/°C, respectively, over the temperature variation range of 20°C to 80°C. Therefore the simultaneous detection of liquid level and temperature can be realized by establishing a measurement inversion matrix. Compared with other liquid level sensors, this sensor is expected to be widely used in the field of liquid level sensing due to its simple structure, high liquid level sensitivity, large liquid level measurement range, and narrow monitoring peak bandwidth.

Finite Element Method study on VLF propagable modes coupling and interference in the anisotropic earth‐ionosphere waveguide

AbstractIn this paper, the coupled‐mode theory is incorporated into the improved frequency‐domain finite element method (FEM) to simulate very low frequency (VLF) propagable modes coupling and interference in the anisotropic Earth‐ionosphere waveguide. The matrix equation of the electric field is solved using parallel lower‐upper factorization technique to speed up the calculation. The method used to determine the propagation constants for different propagable modes is given. After the FEM is validated by comparing simulated results with the measured data, effects of variable geomagnetic information on the attenuation rate, relative phase velocity, mode coupling, and multiple‐mode interference of VLF electromagnetic wave in the anisotropic waveguide are investigated. This work provides an efficient way for improving the prediction accuracy of the VLF communication, positioning, navigation, and timing systems.

Sub-wavelength focused light and optical trapping application based on two-mode interference from an optical micro-/nanofiber

The ability to focus light on a subwavelength scale is essential in modern photonics. Optical microfiber-based sub-wavelength focusing will allow a miniaturized, flexible and versatile tool for many applications such as biomedical imaging and optomechanics. For a separate mode exited from an optical micro-/nanofiber endface, the photons will experience significant diffraction into the free space. This situation can be changed by incorporating two-mode interference along with the specific spatial distributions of both <i> <b>E</b> </i>-field amplitude and phase. Herein we report a novel approach to realizing sub-wavelength focusing based on the two-mode interference exited from an optical microfiber endface. By utilizing specific distributions of <b><i>E</i></b> -field amplitude and phase of two interacting optical modes, interference field patterns with a single focus (e.g., via a two-mode set of HE<sub>11</sub> and HE<sub>12</sub>) or multiple foci (e.g., via a two-mode set of HE<sub>11</sub> and HE<sub>31</sub>) can be obtained. Then, it is proved that the constructed foci will readily facilitate and selective trapping of nanoparticles. Circular polarization of optical mode is utilized in order to bring in angular symmetry of sub-wavelength focusing patterns compared with linear polarized optical modes. Our simulation results show that the smallest focal spot produced from the EH<sub>11</sub> and HE<sub>12</sub> mode interference has a full width at half-maximum (FWHM) of ~ 348 nm (i.e. 0.65<i>λ</i>). Such a subwavelength focusing field is applied to the optical trapping of an 85 nm-diameter polystyrene nanosphere. Further calculation reveals that the stable trapping can be fulfilled with axial and transverse trap stiffness of 11.48 pN/(μm·W) and 64.98 pN/(μm·W), as well as axial and transverse potential well of 101 <i>k</i><sub>B</sub>T/W and 641 <i>k</i><sub>B</sub>T/W via two-mode interference of HE<sub>11</sub> and HE<sub>12</sub>. These values demonstrate the great improvement over conventional tapered fibers. Further investigations show that different foci, via a two-mode set of HE<sub>11</sub> and HE<sub>31</sub>, exhibit unlike trap stiffness and potential wells, justifying the potential for nanoparticle size sorting. Based on the flexible all-fiber device, this subwavelength focusing strategy by two-mode interference may find promising applications in optical manipulation, superresolution optical imaging, data storage and nanolithography.

A Vibration‐Based Quasi‐Real‐Time Cable Force Identification Method for Cable Replacement Monitoring

Tension force is a crucial indicator in reflecting the stressing state of old cables during the cable replacement process. Even though the vibration‐based method is popular in the cable force identification due to its simple calculation process and low cost, the frequency is hard to be recognized with both high time and frequency resolutions attributed to the Heisenberg uncertainty principle, which hinders its application in identifying time‐varying cable force. In this paper, a novel quasi‐real‐time cable force identification method is presented based on a quasi‐ideal time‐frequency analysis method called multi‐synchrosqueezing transform (MSST), by which the cable frequencies can be identified with appreciable time‐frequency resolution. To achieve the identification in a real‐time manner, an Automatic Frequency Order Identification (AFOI) algorithm is developed to recognize the frequency order automatically depending on the MSST result, in which the interference of fake modes and omitted modes to the identification of the actual frequency order is eliminated to a large extent. The performance of the proposed AFOI algorithm and the quasi‐real‐time cable force identification method is evaluated on a practical cable replacement engineering case. Results show that the correct orders of the multiple frequencies received from MSST can be identified along the time domain, which demonstrates the effectiveness of the proposed method. The variation of the tension force of not only the replaced cable but also its neighbor cables is estimated with desired time‐frequency resolution, which promotes the safety state assessment of a cable in a real‐time manner during the replacement process.

Near-moving-wall flows past three tandem elliptical cylinders at low Reynolds number of 150

Dynamic flows past three tandem elliptic cylinders of equal spacing in parallel arrangement with a moving wall are numerically conducted by the lattice Boltzmann method. The gap ratio (G/D, where G and D are the gap between the wall surface and cylinder center and major axis, respectively) from 0.6 to 2.5 and spacing ratio (L/D, where L is the distance of two adjacent cylinder centers) from 1.5 to 10 are examined at Reynolds number of Re = 150 (based on D). The desired analysis correlates variations of hydrodynamic coefficients, wake structures, and spectral analysis in wide space of G/D and L/D with underlying fluid mechanics. The flow is highly adjustable in G/D−L/D space, dividing into six distinct regimes: overshoot, continuous reattachment, alternative reattachment, wavy, meandering, and coshedding, which are spatially classified into four modes because of flow interference, namely, shear layer, primary, two-layered, and secondary vortex shedding modes. The transition between adjacent modes defines three boundaries. The first boundary always occurs behind the middle or downstream cylinder, whereas the second and third boundaries occur between the upstream and middle cylinders and the downstream cylinder wake. Due to the near-wall flow interference, the hydrodynamic coefficients are highly changeable in L/D−G/D space, signifying the crucially lower drag coefficient of the middle and downstream cylinders than that of a single cylinder. A small G/D determines the increase in lift coefficient of the upstream cylinder as a result of the ground effect, while the shadowing effect of the upstream cylinder induces identical Strouhal numbers of the middle and downstream cylinders.

Monitoring Void Fatigue in Solder Layer of IGBT Module Based on Common Mode Interference Spectrum

Monitoring Void Fatigue in Solder Layer of IGBT Module Based on Common Mode Interference Spectrum

Quantitative classification of velocity pulse-like ground motions based on an adaptive response spectrum-based decomposition method

Pulse-like ground motions generally contain low-frequency velocity pulse with large amplitude, which can lead to severe damage or even collapse of near-fault structures. This study aims to proposed an adaptive decomposition method and corresponding identifying approach for pulse-like records. Firstly, an adaptive response spectrum-based decomposition (ARSD) method is proposed to decompose the records into several intrinsic mode functions (IMF) and their periods are identified by peak-point method. The decomposed results are compared with two representative methods, ensemble empirical-mode decomposition (EEMD) and variation mode decomposition (VMD). The results show that the proposed method can effectively avoid the mode mixing appears in the decomposed results by EEMD and generates similar results with those by the VMD. Then the low-frequency pulse is extracted by composing the key IMFs with the period and energy change larger than 0.5 s and 0.1. Based on the results of visual inspection method, the threshold of energy-based pulse indicator factor in general form and exponential form is calibrated to 0.26 and 0.30 respectively. The results show that the exponential form can improve identification rate of pulse-like records. The pulse extraction and classification results of the proposed method are comprehensively compared with three benchmark methods. The classification results by the proposed method are generally consistent with the three methods. Moreover, all the four methods can accurately detect the non-pulse records. And the proposed method could detect the most pulse-like records, followed by the Zhai's method, while the Feng's and Baker's methods detected the least pulse type records. The corresponding identification rates are 91.04%, 80.60%, 63.43%, and 63.06%, respectively. Finally, the periods of the records with single mode and multiple modes estimated by the proposed method and three benchmark methods are compared. The estimated periods of the records with single mode by the proposed method are highly consistent with those by the three benchmark methods, while this consistency for the estimated periods of records with multiple modes is reduced at some extent. This is due to the interference of multiple modes embedded in the records to the pulse identification.

Deconvoluting the Impact of Early-Life Abuse Conditions on the Cyclic Degradation of Lithium-Ion Cells

The successful repurposing of degraded lithium-ion (Li-ion) batteries in second-life applications is a vital step towards achieving a circular economy. While reusing aged Li-cells is a promising way of mitigating their overall environmental footprint, it is crucial to anticipate their future safety and performance characteristics. Unfortunately, predicting these properties is a cumbersome task, essentially caused by limited knowledge of the interference of different degradation modes in the cells’ first life.To still enable estimating of these parameters from a current state, the present study systematically investigates the impact of abusive conditions in an early phase of the cells’ life on their subsequent degradation behavior. For this purpose, individual Li-cells are initially stressed by different measures such as overcharging, deep-discharging, plating, and deliberate combinations of the aforementioned methods. Electrochemical performance indicators are monitored during subsequent cycling of the cells which provides insights into the interdependencies of different degradation modes induced by specific stress conditions. In this manner, it is clarified whether or not the total degradation can be determined by a convolution or a superposition of individual deterioration effects and, thus, be described as a multidimensional state function.This knowledge will finally contribute to a better understanding of the performance and safety behavior of degraded Li-ion batteries which can help to successfully implement them into second-life applications.

A NOVEL MULTIFREQUENCY GPS APP FOR STUDYING OLDER ADULTS: IMPROVING ACCURACY AND RELIABILITY OF DATA

Abstract Acquiring global positioning system (GPS) data can help researchers understand the relationship between older adult’s location/activity and their health, but existing GPS data collection modes suffer from issues with precision, consistency, and acceptability. Some limitations of current GPS mobile apps are satellite service disruption, power saving mode interference, miscalibration of device’s compass, and user-error during data collection which result in missing or inaccurate data. We present a novel multilingual GPS mobile app and live administrative dashboard to address these limitations. The app performs triangulation between GPS satellite data, nearest cellular tower, and WiFi router location data which are processed through a unique GPS algorithm with a mean error of only 1.5 meters. Since GPS data results in coordinates commonly reverse geo-coded to place-based datasets, the accuracy is critical in determining place type or other characteristics. The app is additionally designed with redundancy and fault tolerance in mind to run continuously in the background of a user’s smartphone, so there is no data loss from accidentally closing the application or restarting the phone. Moreover, this new application has a flexible sampling rate ranging from 1 second to 20 minutes. Sampling frequency flexibility can adjust the battery life and reduce the need to charge as frequently. Last, application programming interface (API) integrations allow for live data stream, which can improve monitoring and troubleshooting in the field. For research with older adult populations, these features can not only improve the accuracy of collected data but also increase the acceptability of collecting GPS data.

Optical-domain modulation cancellation method for background-suppression and dual-gas detection in light-induced thermo-elastic spectroscopy

To address the issues of signal saturation and measurement range reduction caused by the background in light-induced thermoelastic spectroscopy (LITES) employing the first harmonic (1 f) modulation, an optical-domain modulation cancellation method (MOCAM) was reported in the 1f-based LITES. A balance laser source with the opposite sine modulation phase as the excitation laser source synchronously excites the quartz tuning fork (QTF) to realize background suppression. By optimizing the modulation amplitude of the balance laser and the modulation phase difference between the two laser sources, the background level was suppressed by two orders of magnitude from ∼ 7 mV to ∼ 18 μV, close to the QTF thermal noise level (∼ 1 μV). Combining the excitation laser with the balance laser enables MOCAM to overcome common mode interferences, e.g. optical path shift, laser power fluctuation, and focus position change. Furthermore, methane and water vapor (CH4/H2O) dual-gas detection based on MOCAM and time-division multiplexing method was demonstrated, and measurement range is enlarged with easy calibration due to zero background. The MOCAM-based 1f-LITES technique delivers effective background suppression and provides robustness to common mode interferences, thus establishes a feasible solution for mobile vehicle or airborne gas monitoring applications with serious environmental disturbances.

High-order orbital angular momentum mode-based phase shift-keying communication using phase difference modulation.

Orbital angular momentum (OAM) mode offers a promising modulation dimension for high-order shift-keying (SK) communication due to its mode orthogonality. However, the expansion of modulation order through superposing OAM modes is constrained by the mode-field mismatch resulting from the rapidly increased divergence with mode orders. Herein, we address this problem by propose a phase-difference modulation strategy that breaks the limitation of modulation orders via introducing a phase-difference degree of freedom (DoF) beyond OAM modes. Phase-difference modulation exploits the sensitivity of mode interference to phase differences, thereby providing distinct tunable parameters. This enables the generation of a series of codable spatial modes with continuous variation within the same superposed OAM modes by manipulating the interference state. Due to the inherent independence between OAM mode and phase-difference DoF, the number of codable modes increases exponentially, which facilitates establishing ultra-high-order phase shift-keying by discretizing the continuous phase difference and establishing a one-to-one mapping between coding symbols and constructed modes. We show that a phase shift-keying communication link with a modulation order of up to 4 × 104 is achieved by employing only 3 OAM modes (+1, + 2 and +3), and the decode accuracy reaches 99.9%. Since the modulation order is exponentially correlated with the OAM modes and phase differences, the order can be greatly improved by further increasing the superimposed OAM modes, which may provide new insight for high-order OAM-based SK communication.

Permutation entropy-based characterization of speckle patterns generated by semiconductor laser light

Semiconductor lasers with optical feedback are stochastic nonlinear systems that can display complex dynamics and abrupt changes when their operation conditions change. Even very small changes can lead to large variations in the spatial and spectral properties of the laser emission. This makes a semiconductor laser with feedback an ideal system for conducting controlled experiments to test data analysis tools to detect and characterize transitions. Here, we identify feedback-induced transitions by analyzing speckle patterns that are generated after the laser light propagates in an optical fiber. Speckle patterns result from the interference of multiple modes, and their statistical properties are understood, but a direct mathematical model does not exist. Here we show the versatility of the correlation length and the permutation entropy as measures for characterizing speckle patterns. Combining entropy and correlation analysis with speckle contrast analysis, we uncover changes that occur when the laser current increases from below to well above the threshold, which unveils the effects of optical feedback on the coherence of the laser emission.

Terahertz plasmonic functional devices enabled by multimode interference

Terahertz integrated devices have attracted great attention due to their potential applications in communication systems. Although some functional devices based on terahertz spoof surface plasmon polariton (SPP) waveguides have been studied, multimode waveguides and multimode interference mechanism have rarely been explored. This work investigates several key functional plasmonic devices based on multi-SPP mode interference in the terahertz regime. The feasibility of multimode transmission on terahertz plasmonic waveguides and control of the propagation modes by varying the waveguide parameters are first investigated. Then, the interference mechanism between two or more propagation modes and the self-imaging principle are applied to plasmonic waveguides. Finally, a series of terahertz plasmonic functional devices such as a coupler, wavelength diplexers, and cascaded devices are proposed and simulated by exploring different interference lengths, frequencies, and cascades via the self-imaging principle. These devices have good performance in transmission response, crosstalk, bandwidth, and footprint, and are expected to play an important role in the development of terahertz on-chip communication systems.

A 330-GHz Radial Power Division/Combination Network Based on Circularly Polarized TE11 Mode

To compensate for severe mode interference and machining difficulties above the W-band of the traditional radial power combining scheme, a radial power division/combination network based on circularly polarized (CP) TE11 mode is designed. Firstly, the amplitude and phase distribution of the branches of a radial power divider under the excitation of CP mode are analyzed. The amplitudes of each branch are approximately equal, and the phase increases/decreases with equal differences. Therefore, a radial power divider with 16 branches based on a septum circular polarizer (SCP) is designed. An orthogonal cascade structure (OCS) and a parallel cascade structure (PCS) are proposed, and it is concluded that to obtain higher transmission efficiency, OCS and PCS should be used respectively when the phase or amplitude difference of SCP is worse. Finally, the power divider and a microstrip probe transition structure are cascaded back-to-back by using OCS, and the power division/combination network is obtained. Simulation results show that at 310-360 GHz, the amplitude difference of the branches of the power divider is less than ±0.35 dB; the combining efficiency of the power division/combination network is greater than 90%. This network has the advantages of single-mode operation, simple structure, and high combining efficiency. In addition, this article provides a feasible solution to the problem of depolarization loss caused by the cascade of SCPs.

A subwavelength insulation panel for acoustic and aeroacoustic sources

A new kind of panel with strong transmission loss, breaking the mass law by 15 dB and composed by a soft solid plate with embedded solid cylindrical inclusions is studied numerically and experimentally. The presence of the inclusions introduces resonant and antiresonant phenomena in the subwavelength regime (the thickness is 30 times smaller than the equivalent wavelength in air), leading to an elastic band-gap and a destructive modal interference able to interact with each other. We also report on an experimental campaign demonstrating that the panel is very effective at insulating aeroacoustic sources (tested up to Mach 0.6), showing even better performance than with an acoustic source excitation. A new analysis tool, the vibroacoustic band diagram, is introduced to better apprehend theoretically all these results.

Statistical inversion of normal‐mode interference spectral parameter in ocean waveguide

AbstractA statistical inversion method of estimating normal mode interference spectral parameters (including waveguide invariance and interference frequency) from one‐dimensional broadband sound intensity spectrum (1D BSIS) is presented. First, the interference phase of 1D BSIS is compensated by a non‐linear factor for each pair of unknown parameters in a prior parameter space. Second, the singular value decomposition is performed for a data matrix, which is constructed by the phase‐compensated BSIS. Then, a misfit function is defined based on both the maximum singular value and the corresponding singular vector of the data matrix. Finally, the posterior probability distributions of unknown parameters are analysed based on statistical inversion theory. This method is suitable for the situation using a single receiver and without any environmental information. Numerical simulations illustrate the validity of the presented method.