Order Harmonics Research Articles

Generation of a switchable and tunable rectangular pulse and multi-pulse with different peak powers at the L-band

A novel, to our knowledge, L-band erbium-doped fiber laser, utilizing a nonlinear optical loop mirror (NOLM) as a mode-locker, is presented in this study. Through precise adjustments of the polarization controllers (PCs), the laser achieves the generation of rectangular pulses with distinct single wavelengths, λ1=1593nm and λ2=1571nm, as well as dual-wavelength operation. The laser’s operational mode can extend further to include harmonic mode-locking (HML). Furthermore, the investigation reveals the emergence of trapezoidal pulses and low-peak-power rectangular pulses within proximity of the conventional rectangular pulses. Notably, the evolutions of these low-peak-power pulses with the pump power also adhere to the peak power clamping (PPC) effect. Remarkably, the relative positioning of these pulses remains consistent across varying pump power levels or harmonic orders. Intriguingly, the evolution of the trapezoidal pulse with respect to pump power stands in stark contrast to that of the h-shaped pulse.

Harmonizing data on correlates of sleep in children within and across neurodevelopmental disorders: lessons learned from an Ontario Brain Institute cross-program collaboration.

There is an increasing desire to study neurodevelopmental disorders (NDDs) together to understand commonalities to develop generic health promotion strategies and improve clinical treatment. Common data elements (CDEs) collected across studies involving children with NDDs afford an opportunity to answer clinically meaningful questions. We undertook a retrospective, secondary analysis of data pertaining to sleep in children with different NDDs collected through various research studies. The objective of this paper is to share lessons learned for data management, collation, and harmonization from a sleep study in children within and across NDDs from large, collaborative research networks in the Ontario Brain Institute (OBI). Three collaborative research networks contributed demographic data and data pertaining to sleep, internalizing symptoms, health-related quality of life, and severity of disorder for children with six different NDDs: autism spectrum disorder; attention deficit/hyperactivity disorder; obsessive compulsive disorder; intellectual disability; cerebral palsy; and epilepsy. Procedures for data harmonization, derivations, and merging were shared and examples pertaining to severity of disorder and sleep disturbances were described in detail. Important lessons emerged from data harmonizing procedures: prioritizing the collection of CDEs to ensure data completeness; ensuring unprocessed data are uploaded for harmonization in order to facilitate timely analytic procedures; the value of maintaining variable naming that is consistent with data dictionaries at time of project validation; and the value of regular meetings with the research networks to discuss and overcome challenges with data harmonization. Buy-in from all research networks involved at study inception and oversight from a centralized infrastructure (OBI) identified the importance of collaboration to collect CDEs and facilitate data harmonization to improve outcomes for children with NDDs.

Relative strengths of sum and difference frequency generation in perturbative high harmonic wave mixing

High harmonic generation (HHG) modulated by a weak laser field allows the perturbative wave mixing process which involves sum and difference frequency generations (SFG and DFG). The relative strengths of SFG and DFG have been extensively discussed in the literature but are still ambiguous. Here we experimentally study the relative strengths between SFG and DFG channels by applying a frequency-offset second-harmonic perturbing laser field collinearly in a thin gaseous nonlinear medium. It shows that SFG is favored for low harmonic orders, but DFG dominates for high-energy photons, when only short trajectories of high harmonics are considered. A semi-classical model incorporating both modulations to the tunneling ionization and the electron propagation steps by the perturbing laser field for a train of attosecond pulses explains the experimental results.

Tidal Heating in a Subsurface Magma Ocean on Io Revisited

AbstractWe investigate the tidal dissipation in Io's hypothetical fluid magma ocean using a new approach based on the solution of the 3D Navier‐Stokes equations. Our results indicate that the presence of a shallow magma ocean on top of a solid, partially molten layer leads to an order of magnitude increase in dissipation at low latitudes. Tidal heating in Io's magma ocean does not correlate with the distribution of hot spots, and is maximum for an ocean thickness of about 1 km and a viscosity of less than 104 Pa s. Due to the Coriolis effect, the k2 Love number can depend on the harmonic order. We show that the analysis of k2 may not reveal the presence of a fluid magma ocean if the ocean thickness is less than 2 km. If the fluid layer is thicker than 2 km, k20 ≈ k22/2 ≈ 0.7.

Simulation Analysis of Phase Jitter in Differential Sampling of AC Waveforms Based on the Programmable Josephson Voltage Standard

The effect of phase jitter on differential sampling using the programmable Josephson voltage standard (PJVS) system is studied in this paper. A phase jitter model is established for the measured signal, and compensation coefficients for phase jitter removal are derived for three different post-processing methods based on the discrete Fourier transform algorithm (DFT). Based on our analysis, the phase jitter compensation coefficients are determined by the phase jitter angle distribution and harmonic order. Furthermore, after analyzing and simulating various common distributions, the phase jitter compensation coefficients have been verified. The simulation shows that when the standard deviation of the phase jitter angle is 20 ns, and the frequency of the measuring waveform is 3.46 kHz, the influence of the phase jitter is 1 × 10−7. The results of the simulation indicate that, in the differential sampling of AC waveforms using a PJVS system, phase jitter is one of the error terms for an uncertainty budget that cannot be neglected, particularly as the frequency of the measured waveforms increases.

Controlling the bandwidth of high harmonic emission peaks with the spectral polarization of the driver.

We demonstrate a high harmonic-generation scheme that offers control over the bandwidth of the spectral peaks. The scheme uses a vectorial two-color driver with close central frequencies, generated by spectrally splitting a linearly polarized input femtosecond-duration laser pulse and subsequently recombining the two halves after their polarizations are made cross-elliptical and counter-rotating. This results in the generation of new emission channels that coalesce into broad odd-integer HHG peaks, the bandwidth of each being proportional to the frequency difference between the two colors, to the harmonic order and inversely proportional to the driver fields' ellipticities. Peak broadening to the extent that a supercontinuum is formed is also demonstrated. This source will find use in HHG applications benefiting from high-flux broadband extreme ultraviolet radiation, such as attosecond transient absorption spectroscopy.

High-harmonic spin-shearing interferometry for spatially resolved EUV magneto-optical spectroscopy

We present a method for achieving hyperspectral magnetic imaging in the extreme ultraviolet (EUV) region based on high-harmonic generation (HHG). By interfering two mutually coherent orthogonally-polarized and laterally-sheared HHG sources, we create an EUV illumination beam with spatially-dependent ellipticity. By placing a magnetic sample in the beamline and sweeping the relative time delay between the two sources, we record a spatially resolved interferogram that is sensitive to the EUV magnetic circular dichroism of the sample. This image contains the spatially-resolved magneto-optical response of the sample at each harmonic order, and can be used to measure the magnetic properties of spatially inhomogeneous magnetic samples.

Investigation of spectro-temporal high-order sideband generation from transition metal dichalcogenides [Invited

High-order sideband generation (HSG) in semiconductors under intense terahertz fields has been extensively studied, because it provides essential information for studying ultrafast dynamics in strong-field-dressed quantum materials. In particular, transition metal dichalcogenides (TMDCs), characterized by their unique band structures, provide an exemplary semiconductor system to explore the influence of material band structure on strong-field-induced modulation of HSG. In this work, we investigate the spectro-temporally resolved HSG from different bulk TMDC materials. Our results reveal distinct temporal HSG spectra, which can be attributed to the different absorption behaviors of these materials. Simulations based on the strong-field approximation and Floquet theory can well reproduce the experimental observations. Our work also delves into the spectro-temporal interference that emerges when neighboring harmonic orders overlap in the HSG spectrum. This work enhances our understanding of high-order sideband dynamics in strong-field-dressed semiconductors, offering insights for applications in spectrum- and phase-resolved ultrafast measurements.

A full-duplex 5G mobile fronthaul based on analog RoF-WDM-PON supporting flexible frequency-band switching with colorless and simple RRH

In this paper, a full-duplex analog radio over fiber scheme based on wavelength division multiplexing passive optical network (A-RoF-WDM-PON) is proposed for the 5G mobile fronthaul (MFH). For the downlink, a flexible switching of the frequency-band covering sub-6G and millimeter wave (MMW) is enabled by the combination of a polarization controller and a polarizer. The colorless and simple remote radio head (RRH) is realized by the wavelength reuse and phase modulation of the upstream (US) signal. For the uplink, the high-frequency US signal can be photonic down-converted to an immediate frequency (IF) with the assistance of the 2nd order harmonic of the electrical local oscillator (ELO) and the coherent detection is employed to improve the receiver sensitivity. The proposed scheme is experimentally demonstrated by the transmission of a 100-Msym/s 16-QAM downstream (DS) signal over 25 km single-mode fiber (SMF) and a 100-Msym/s 16-QAM US signal over 10 km SMF. The experimental results show that the error vector amplitudes (EVMs) for downlink at frequency bands of 3.5 GHz, 12.5 GHz and 21.5 GHz are 6.30%, 5.90% and 7.15% respectively. The EVM of US signal at 19 GHz is 7.64%. The EVM performance versus the received optical power for both up- and down-link are also measured. Additionally, a dual-wavelength multiplexing transmission is carried out, the measured EVMs in one wavelength channel are 7.65%, 7.63%, 11.33% and 8.47%, and the EVMs for the other wavelength channel are 8.09%, 7.74%, 11.45% and 8.42%, which meets the standard of the Third Generation Partnership Program (3GPP).

Spin Faraday waves in periodically modulated spin-orbit-coupled Bose gases

This paper investigates the formation of Spin Faraday waves in spin-orbit-coupled Bose-Einstein condensate under the stripe phase and explores the dispersion relation under three different phases. We discover that the SFW exhibit temporal and spatial patterns, and appear with resonant waves and higher order harmonics when the interaction is modulated periodically. SFW can be excited even when the modulation frequency resonates with the trap frequency. Furthermore, we study the dispersion relation of these Faraday modes through periodic modulation, which agrees well with our theoretical results under three quantum phases. Our work indicates novel physical phenomena originating from the introduction of spin-orbit coupling and provides a possible method for studying the dispersion of Bose gases.

Assessing Micro Wall-Thinning Damage in Aluminum Frames of Subsonic Speed Vehicles: A Comprehensive Approach Integrating Higher - Order Harmonic Nonlinear Guided Wave Analysis and Convolutional Neural Networks

Assessing Micro Wall-Thinning Damage in Aluminum Frames of Subsonic Speed Vehicles: A Comprehensive Approach Integrating Higher - Order Harmonic Nonlinear Guided Wave Analysis and Convolutional Neural Networks

Explainable Artificial Intelligence Approach for Diagnosing Faults in an Induction Furnace

For over a century, induction furnaces have been used in the core of foundries for metal melting and heating. They provide high melting/heating rates with optimal efficiency. The occurrence of faults not only imposes safety risks but also reduces productivity due to unscheduled shutdowns. The problem of diagnosing faults in induction furnaces has not yet been studied, and this work is the first to propose a data-driven framework for diagnosing faults in this application. This paper presents a deep neural network framework for diagnosing electrical faults by measuring real-time electrical parameters at the supply side. Experimental and sensory measurements are collected from multiple energy analyzer devices installed in the foundry. Next, a semi-supervised learning approach, known as the local outlier factor, has been used to discriminate normal and faulty samples from each other and label the data samples. Then, a deep neural network is trained with the collected labeled samples. The performance of the developed model is compared with several state-of-the-art techniques in terms of various performance metrics. The results demonstrate the superior performance of the selected deep neural network model over other classifiers, with an average F-measure of 0.9187. Due to the black box nature of the constructed neural network, the model predictions are interpreted by Shapley additive explanations and local interpretable model-agnostic explanations. The interpretability analysis reveals that classified faults are closely linked to variations in odd voltage/current harmonics of order 3, 11, 13, and 17, highlighting the critical impact of these parameters on the model’s prediction.

Small-signal modeling comparison of dual active bridge converter

The dual active bridge (DAB) converter is a versatile DC-DC converter, which has AC components in the high-frequency transformer within the converter topology as well as DC components at the input and output sides. These AC components are constructed from infinite sinusoids of multiples of the converter's switching frequency. Different approaches have been proposed to model the DAB converter. The generalized averaging modeling (GAM) includes only the first order harmonic of the inductor current with the DC components of the input and output voltages and currents. For better model accuracy, harmonic-domain models have been employed, where the model includes all the harmonics of all the model state variables up to an arbitrary harmonic index. While the harmonic model provides a systematic approach to include the harmonics, this increases the model complexity. To avoid this complexity, the flexible harmonic model is used where harmonics can be selected per each state variable without needing to be in successive order. The aforementioned modeling approaches have been implemented on the DAB converter. This paper aims to compare between the dynamic performance of GAM and the harmonic modeling approaches under different disturbances, where the GAM approach provided a simple model with acceptable results that can be used for controller design, while the LTP model provided a more complex model with better accuracy that is suitable for harmonic studies. The models have been validated and compared using simulations executed on MATLAB /Simulink environment.

Leakage Current Harmonic Index as A Diagnostic Technique for Tool to Assess the Surface Condition Assessment of Aged Insulator Surface Under Varying Humidity

Leakage current has been widely utilized as an effective means to monitor the pollution severity of outdoor insulators. The indices of the odd harmonic components of the leakage current have proven to be reliable indicators of insulator performance, particularly in the third to fifth harmonic orders. However, significant challenges exist in using these indices to monitor and classify the leakage current of aged insulators under varying harmonic and pollution conditions. This paper introduces the harmonic index K((3/(5+7) ) which employs third up to seventh odd harmonic component of the leakage current as a diagnostic tool to determine the pollution severity of aged insulators under light, medium and heavy contamination levels. The experiments were conducted using 12 different sets of 11kV insulators with varying degrees of aging. The results indicate that the harmonic index Ki for new and moderately aged insulators decreases with an increase in contamination and is lower than that of heavily aged insulators.

Intra-oscillator high harmonic source reaching 100-eV photon energy

Resonant enhancement inside an optical cavity has been a wide-spread approach to increase efficiency of nonlinear optical conversion processes while reducing the demands on the driving laser power. This concept has been particularly important for high harmonic generation XUV sources, where passive femtosecond enhancement cavities allowed significant increase in repetition rates required for applications in photoelectron spectroscopy, XUV frequency comb spectroscopy, including the recent endeavor of thorium nuclear clock development. In addition to passive cavities, it has been shown that comparable driving conditions can be achieved inside mode-locked thin-disk laser oscillators, offering a simplified single-stage alternative. This approach is less sensitive to losses thanks to the presence of gain inside the cavity and should thus allow higher conversion efficiencies through tolerating higher intensity in the gas target. Here, we show that the intra-oscillator approach can indeed surpass the much more mature technology of passive enhancement cavities in terms of XUV flux, even reaching comparable values to single-pass sources based on chirped-pulse fiber amplifier lasers. Our system operates at 17 MHz repetition rate generating photon energies between 60 eV and 100 eV. Importantly, this covers the highly attractive wavelength for the silicon industry of 13.5 nm at which our source delivers 60 nW of outcoupled average power per harmonic order.

Harmonic domain-wall dark pulse generation using unpumped thin-core thulium fiber as interferometer

In this work, the harmonic domain-wall dark pulse is experimentally demonstrated in C-band fiber laser. The domain-wall dark pulse was self-started at pump power of 112 mW. The fundamental dark pulse repetition rate was measured as 0.96 MHz, pulse duration of 250 ns and highest average pulse energy of 3.24 nJ. As the power increased, dark pulses up to the 7th harmonic order were visualized and quantified. Pulse temporal width reduced as harmonic order increased, with the minimum pulse width of 60 ns recorded in the 7th order. The harmonic dark pulse fiber laser demonstrated adequate stability, with signal-to-noise ratios above 50 dB throughout all harmonic operations. The endeavor of harmonic dark pulse dark soliton could lay the groundwork for future sustainable industrial growth.

Clustering-Based Classification of Polygonal Wheels in a Railway Freight Vehicle Using a Wayside System

Polygonal wheels are one of the most common defects in train wheels, causing a reduction in comfort levels for passengers and a higher degradation of vehicle and track components. With the aim of contributing to the safety and reliability of railway transport, this paper presents the development of an innovative methodology for classifying polygonal wheels based on a wayside system. To achieve that, a numerical train-track interaction model was adopted to simulate the passage of a freight train over a virtual wayside monitoring system composed of a set of accelerometers installed on the rails. Then, the acquired acceleration time series was transformed to a frequency domain using a Fast Fourier transform (FFT), and on this data, damage-sensitive features were extracted. The features based on Principal Component Analysis (PCA) showed great sensitivity to the harmonic order, while the ones based on Continuous Wavelet Transform (CWT) model showed great sensitivity to the defect amplitude. One step further, all features are merged using the Mahalanobis distance in order to obtain a damage index strongly correlated with the polygonal defect. Finally, a cluster analysis allowed the automatic classification of polygonal wheels, according to the harmonic order (harmonic-based) and defect amplitude (amplitude-based). The proposed methodology demonstrated high efficiency in identifying different types of polygonal wheels using a minimum layout of two sensors.

Analysis of pole pair number impact on single-sided linear induction machine performances

This paper presents a parametric study of linear induction motor for design purpose. The chosen mathematical model uses a 2D formulation with magnetic vector potential A. The implementation of the model is carried out with the finite element method on the free platform Gmsh-GetDP. Circuit model is coupled to FE model so that constant voltage supply mode can be considered. This work aims to highlight the effect of the pole pair number on the characteristics and the performances of the linear induction machine through two numerical models associated to an analytical one. Furthermore, the study shows the effect of the pole pair number on the phase imbalance and the spatial harmonic spectrum of the machine. Reducing this imbalance and higher order harmonics presence will increase machine performances.

Investigation of electromagnetic processes in the case of static eccentricity of a two-pole induction motor with a short-circuited rotor

Purpose. Correction of the mathematical model of electromagnetic processes in a two-pole induction motor with a short-circuited rotor, taking into account static rotor eccentricity to identify diagnostic correlations. Methodology. Analytical modeling using the method of specific magnetic conductivity, mathematical modeling of electromagnetic fields in a three-phase induction motor with a short-circuited rotor using methods of electromagnetic field theory and finite element methods. Obtained results. The necessity of improving mathematical models for induction motors with short-circuited rotors to establish new or refine connections between diagnostic features and diagnosed defects has been demonstrated. Refined mathematical expressions for calculating the specific conductivity of non-uniform air gaps in induction motors with static eccentricity are provided. Modeling was performed using the FEMM environment for a statically eccentric two-pole induction motor with a short-circuited rotor. It has been proven that the harmonic order values obtained using the numerical-field method are consistent with those obtained analytically. Findings. Based on the field approach and using the finite elements method, an analysis of the distribution of magnetic field in a two-pole induction motor with a short-circuited rotor was conducted. Harmonic analysis of the magnetic field in the air gap was performed to identify the fundamental harmonic and higher and lower-order harmonics when eccentricity occurs. The influence of static rotor eccentricity on the electromagnetic processes of the induction motor was analyzed. Practical value. The results of the study can be utilized for functional diagnosis of the rotor winding of induction motors based on the radial component of the magnetic field. This will contribute to enhancing the reliability of induction motors and enable the prevention of failure in induction motors with short-circuited rotors.

Higher-order composition of short- and long-period effects for satellite analytical ephemeris computation

The construction of an analytic orbit theory in closed form of the eccentricity that takes into account the main effects of the Geopotential is notably simplified when splitting the removal of periodic effects in several stages. Conversely, this splitting of the closed-form analytical solution into several transformations reduces the evaluation efficiency for dense ephemeris output. However, the advantage is twofold when the different parts of the mean-to-osculating transformation are composed into a single transformation. To show that, Brouwer’s solution is extended to the second order of the zonal harmonic of the second degree by the sequential elimination of short and long period terms. Then, the generating functions of the different transformations are composed into a single one, from which a single mean-to-osculating transformation is derived. The new, unique transformation notably speeds up the evaluation process, commonly improving evaluation efficiency by at least one third with respect to the customary decomposition of the analytical solution into three different parts.