Modal Power Research Articles

Realizing High-Pulse-Energy Large-Angular-Momentum Beams by Astigmatic Transformation of Geometric Modes in an Nd:YAG/Cr4+:YAG Laser

An off-axis pumped Nd:YAG/Cr4+:YAG laser under different degenerate cavity conditions has been thoroughly studied to generate high-pulse-energy geometric modes for further beam transformation. Because of the employment of Nd:YAG gain crystal provides a flexible choice of cavity length to achieve efficient passively Q-switched (PQS) operation, various PQS geometric modes with stable spatial structures are generated. Moreover, it is experimentally confirmed that the output energy and peak power of the PQS geometric modes can easily reach up to over 100 μJ and 10 kW with fairly stable pulse trains in pure linear polarization. By using an astigmatic mode converter (AMC) to transform the planar geometric modes into the circular geometric modes, various high-energy vortex beams with large angular momentum and diverse phase structures are successfully realized to offer a promising light source for further application. The propagation evolution of the transformed geometric modes through the AMC was also analyzed theoretically to offer useful insights for the formation of the geometric vortex beams.

The Usage of a Locomotive Tractive Power in the Different Operating Modes and the Efficiency Control

The Usage of a Locomotive Tractive Power in the Different Operating Modes and the Efficiency Control

Analyzing modal power in multi-mode waveguide via machine learning.

A machine learning assisted modal power analyzing scheme designed for optical modes in integrated multi-mode waveguides is proposed and studied in this work. Convolutional neural networks (CNNs) are successfully trained to correlate the far-field diffraction intensity patterns of a superposition of multiple waveguide modes with its modal power distribution. In particular, a specialized CNN is trained to analyze thin optical waveguides, which are single-moded along one axis and multi-moded along the other axis. A full-scale CNN is also trained to cross-validate the results obtained from this specialized CNN model. Prediction accuracy for modal power is benchmarked statistically with square error and absolute error distribution. It is found that the overall accuracy of our trained specialized CNN is very satisfactory for thin optical waveguides while that of our trained full-scale CNN remains nearly unchanged but the training time doubles. This approach is further generalized and applied to a waveguide that is multi-moded along both horizontal and vertical axes and the influence of noise on our trained network is studied. Overall, we find that the performance in this general condition keeps nearly unchanged. This new concept of analyzing modal power may open the door for high fidelity information recovery in far field and holds great promise for potential applications in both integrated and fiber-based spatial-division demultiplexing.

Small business electricity disaggregation: Where can we improve? Towards increased transparency of appliance modal parameters

Small commercial buildings (<50,000 ft2 in floor area) consume 44% of all U.S. commercial primary electricity, with plug loads accounting for 31% of that portion and growing. In response, a bottom-up building energy assessment resource (BEAR) was previously developed as a practical approach to disaggregating building energy use, including plug loads. This article examines the performance of BEAR in estimating plug load consumption, specifically appliance energy consumption, through use of smart meters in two building types, food service and office.Results of the analysis reveal that BEAR is capable of providing building stakeholders with meaningful energy information. Accuracy of BEAR's energy consumption estimates could be improved by 25% to 59% through better data on modal (i.e. appliance operating mode such as standby mode) usage and power demand, respectively. These results stress the importance of detailed modal information, because when modal power information was available the median difference between BEAR and the smart meter measured data was 36% compared with 223% in appliances where modal data was not available. In response to these findings, this study develops and presents energy contour plots, a visual tool for plotting modal usage and modal power in a two-dimensional form of energy consumption contours. Moreover, it is the recommendation of this study that increased transparency of modal power be implemented at the manufacturer label or specification to achieve increased accuracy of targeted energy improvements.

Temperature insensitive low-loss optical connection for automotive gigabit plastic optical fiber communication

Step-index plastic optical fibers (SI-POFs) have already been implemented in automotive optical communication because they offer some significant advantages; they are free from electromagnetic noise and are appropriate for reliable data transmission in harsh environment applications. In current systems, an air gap exists between the fiber connections, and the gap size changes because of temperature variations. We propose and demonstrate an approach for the SI-POF in-line connection, which is targeted for automotive gigabit optical communication. We designed and fabricated an up-tapered ferrule and inserted an index matching material into the gap. By using the up-tapered ferrule, we obtained more stable insertion loss, which is proven by the heat cycle tests. By inserting the index matching material, the insertion loss becomes lower. Moreover, an encircled angular flux evaluation also confirmed that our approach does not change the modal power distribution of the fiber.

Quantum Zeno Effect assisted Spectroscopy of a single trapped Ion

The quantum Zeno effect (QZE) is not only interesting as a manifestation of the counterintuitive behavior of quantum mechanics, but may also have practical applications. When a spectroscopy laser is applied to target atoms or ions prepared in an initial state, the Rabi flopping of an auxiliary transition sharing one common level can be inhibited. This effect is found to be strongly dependent on the detuning of the spectroscopy laser and offers a sensitive spectroscopy signal which allows for high precision spectroscopy of transitions with a small excitation rate. We demonstrate this method with direct frequency comb spectroscopy using the minute power of a single mode to drive a dipole allowed transition in a single trapped ion. Resolving the individual modes of the frequency comb demonstrates that the simple instantaneous quantum collapse description of the QZE can not be applied here, as these modes need several pulses to build up.

Polarization output power stabilization of a vertical-cavity surface-emitting laser

This paper provides an experimental investigation of the polarization stabilization at the output power of an 850 nm vertical-cavity surface-emitting laser (VCSEL) with optical feedback (OF) and a range of polarization angles, OF strength, and the bias current. The VCSEL’s polarization stabilization is evaluated using the extinction ratio measurements of the optical output power of the polarization modes of the VCSEL. The results clearly show that rotation of the polarization angle and the OF level can radically change the polarization stabilization of the VCSEL. Both the polarization angle and OF introduce polarization switching (PS) and instability in the optical output power of the VCSEL. Consequently, these lead to performance degradation of the VCSEL in terms of the operating point and the modulation bandwidth. At a fixed OF level of −7 dB, polarization destabilization is first observed at 45° with the increasing level of polarization angle, whereas for the fixed polarization angles of 40° and 90°, polarization destabilization is observed at −14.5 dB and −14 dB, respectively, with the increasing level of orthogonal OF. We show that, with parallel OF, no PS is observed over the entire OF level. The results also indicate that the VCSEL with no polarization angle requires higher levels of OF in order to ensure PS compared with the case with the polarization angle.

Theoretical analysis of the SRS-induced mode distortion in large-mode area fiber amplifiers

In this paper, the spectral evolution properties of different transverse modes with the stimulated Raman scattering (SRS) effect are analyzed in large-mode-area (LMA) fiber amplifiers for the first time. Both the ratios of laser power in Raman Stokes light and high order modes (HOMs) can be calculated through the comprehensive analysis of transverse mode competition and nonlinear transverse mode coupling processes. The theoretical study reveals that SRS-induced inter-modal wave mixing (IM-WM) effect would transfer power from signal light in LP01 mode to Raman Stokes light in LP11 mode and lead to the onset of the mode distortion phenomenon in high-power LMA fiber amplifiers. Different from the traditional thermal-induced mode instability (MI) phenomenon, the SRS-induced mode distortion could occur by just with the contribution of quantum noise.

Proposed phase plate for superimposed orbital angular momentum state generation.

In this letter, a quadratic phase plate (QPP) whose thickness increases quadratically with azimuthal angle φ is proposed. When a beam with initial topological charge m (m could be an arbitrary integer) is passed through the plate, quadratic phase modulation can be expected to expand the initial single orbital angular momentum (OAM) mode to a superimposed OAM state. The obtained multi-OAM state exhibits a comb-like OAM spectrum, which shows a flat region. The power variation of the OAM modes within the flat region is less than 3 dB, while the power for the OAM modes with charge numbers out of the flat region decays rapidly. Moreover, the number of OAM modes within the flat region can reach dozens. This may have potential applications in the field of communication, quantum information and optical manipulation, etc.

Simplified models of the ITER vacuum vessel for global seismic analyses

In order to characterize the behaviour of the ITER Tokamak during seismic events, it is desirable to integrate Finite Element (FE) models of the Tokamak into the model of the building (Tokamak complex). Detailed FE models exist for each of the main Tokamak systems, but these are so large that combining them is computationally impractical.The aim of this paper is to present work performed on the creation of simplified models of the ITER Vacuum Vessel (VV) for use in global seismic analyses.Two different methodologies have been considered for creating simplified models whose dynamic behaviour matches that of a detailed benchmark model. In the first method, a coarse mesh representing the shape of the VV is created. The element properties of this mesh are then modified using optimization algorithms until the desired dynamic behaviour is achieved.The second method makes use of substructuring. In order to minimize the wavefront (and hence computational time), the simplified model is created from multiple superelements, each representing part of the VV.The suitability of the simplified model based on substructuring is quantified by means of the Modal Assurance Criterion (MAC) and Power Spectrum Density (PSD) analysis.

As a Matter of Force—Systematic Biases in Idealized Turbulence Simulations

Abstract Many astrophysical systems encompass very large dynamical ranges in space and time, which are not accessible by direct numerical simulations. Thus, idealized subvolumes are often used to study small-scale effects including the dynamics of turbulence. These turbulent boxes require an artificial driving in order to mimic energy injection from large-scale processes. In this Letter, we show and quantify how the autocorrelation time of the driving and its normalization systematically change the properties of an isothermal compressible magnetohydrodynamic flow in the sub- and supersonic regime and affect astrophysical observations such as Faraday rotation. For example, we find that δ-in-time forcing with a constant energy injection leads to a steeper slope in kinetic energy spectrum and less-efficient small-scale dynamo action. In general, we show that shorter autocorrelation times require more power in the acceleration field, which results in more power in compressive modes that weaken the anticorrelation between density and magnetic field strength. Thus, derived observables, such as the line-of-sight (LOS) magnetic field from rotation measures, are systematically biased by the driving mechanism. We argue that δ-in-time forcing is unrealistic and numerically unresolved, and conclude that special care needs to be taken in interpreting observational results based on the use of idealized simulations.

Control Al/Mg intermetallic compound formation during ultrasonic-assisted soldering Mg to Al

To prevent the formation of Al/Mg intermetallic compounds (IMCs) of Al3Mg2 and Al12Mg17, dissimilar Al/Mg were ultrasonic-assisted soldered using Sn-based filler metals. A new IMC of Mg2Sn formed in the soldered joints during this process and it was prone to crack at large thickness. The thickness of Mg2Sn was reduced to 22 μm at 285 °C when using Sn-3Cu as the filler metal. Cracks were still observed inside the blocky Mg2Sn. The thickness of Mg2Sn was significantly reduced when using Sn-9Zn as the filler metal. A 17 μm Mg2Sn layer without crack was obtained at a temperature of 200 °C, ultrasonic power of Mode I, and ultrasonic time of 2 s. The shear strengths of the joints using Sn-9Zn was much higher than those using Sn-3Cu because of the thinner Mg2Sn layer in the former joints. Sn whiskers were prevented by using Sn-9Zn. A cavitation model during ultrasonic assisted soldering was proposed.

A Novel Electromagnetic Power‐Based Characteristic Mode for Magnetodielectric Materials

AbstractIn this paper, we focus on the characteristics of electromagnetic power of characteristic modes (CMs) for magnetodielectric materials (MDM). A generalized integral form of Poynting's theorem is proposed. Based on the generalized integral form of Poynting's theorem, an explicit formulation for electromagnetic power of traditional volume integral equation‐based CM and Poggio, Miller, Chang, Harrington, Wu, and Tsai‐based CM of homogeneous MDM is presented for the first time. Furthermore, from the concept of electromagnetic power, a novel electromagnetic power‐based CM for MDM is proposed. Numerical results are given to show that the proposed CM is effective in solving scattering problem.

Energy harvesting sensitivity analysis and assessment of the potential power and full car dynamics for different road modes

Abstract Automobiles are dissipating a considerable amount of vibration energy that is worth of being harvested where it can be exploited in different applications. For a full vehicle suspension assembly, the conflict between the potentially harvested energy and vehicle dynamics represented by ride quality and road safety and handling was comprehensively illustrated for different input modes. The discrepancy between the bounce input mode and the roll input mode was also sufficiently clarified based on an extensive parametric analysis covering the design parameters and the operational parameters as well. Comprehensive simulations were then conducted to estimate the amount of wasted energy in vehicle suspension system for different types of cars (passenger, bus, truck, and off-road vehicle), besides the potential harvested power was quantified for different standard driving cycles (NEDC, WLTP, HWFET, and FTP). Based on that, a 7-DOF full car suspension model was implemented in Matlab/Simulink environment and induced by different levels of road irregularities. The findings of this paper showed that the vibration intensity levels changed clearly in the complex input mode that reflects a realistic view of the real vehicle dynamics on the roads compared to the ideal results from the bounce input mode. Our results also indicate that a potential power up to 420 W can be collected considering standard driving patterns and roll mode input. The analysis indicates that the overloaded vehicles are suitable for the energy harvesting system based on the harvestable energy per unit cost.

Modeling guided wave excitation in plates with surface mounted piezoelectric elements: coupled physics and normal mode expansion

Guided waves have been extensively studied and widely used for structural health monitoring because of their large volumetric coverage and good sensitivity to defects. Effectively and preferentially exciting a desired wave mode having good sensitivity to a certain defect is of great practical importance. Piezoelectric discs and plates are the most common types of surface-mounted transducers for guided wave excitation and reception. Their geometry strongly influences the proportioning between excited modes as well as the total power of the excited modes. It is highly desirable to predominantly excite the selected mode while the total transduction power is maximized. In this work, a fully coupled multi-physics finite element analysis, which incorporates the driving circuit, the piezoelectric element and the wave guide, is combined with the normal mode expansion method to study both the mode tuning and total wave power. The excitation of circular crested waves in an aluminum plate with circular piezoelectric discs is numerically studied for different disc and adhesive thicknesses. Additionally, the excitation of plane waves in an aluminum plate, using a stripe piezoelectric element is studied both numerically and experimentally. It is difficult to achieve predominant single mode excitation as well as maximum power transmission simultaneously, especially for higher order modes. However, guidelines for designing the geometry of piezoelectric elements for optimal mode excitation are recommended.

Electromagnetic reflection\u2013transmission problems in a Wilson basis: fiber-optic mode-matching to homogeneous media

The Wilson basis features strong localization in both the spatial and the spectral domain. This enables us to efficiently describe high-frequency wavefields through a parsimonious set of coefficients. By choosing a single universal basis to expand fields, one effectively detaches scattering problems from the specific design of optical waveguides and components that form an optical interface. Equipped with a sparse, diagonally-dominant translation operator, the Wilson basis functions are convenient building blocks to address scattering problems in a more general setting. The physical interface may be reconfigured, while preserving the computational effort of the initial expansion. In this paper, we demonstrate optical reflection–transmission problems for interfaces between optical fibers and homogeneous media. In particular, we treat the construction of one-way propagating electromagnetic fields in the Wilson basis that are generated by Wilson-basis discretized equivalent dipole-source distributions. The Green’s function spectral integrals benefit from the strong localization to achieve good convergence. The decomposition of a wavefield in one-way forward and backward propagating wavefields is the result of careful construction of equivalent sources, and is effectively a Wilson-basis discretized Poincaré–Steklov operator. The decomposition of each and every guided fiber mode to one-way forward and backward propagating fields in homogeneous space can be accomplished in such a way that the boundary conditions are satisfied. These one-way propagating fields subsequently serve as building blocks for the decomposition of arbitrary incident fields, so that the scattering problems are properly solved. The reflection due to a guided mode as excitation is the same as the reflection due to the specific excitation of the same but backward propagating mode up to the accuracy of the numerical quadratures. Upon illuminating the fiber through a complex-source beam wavefield for a number of lateral steps, the Wilson basis formulation immediately produces the corresponding change in the modal power distribution.

Numerical study on supercontinuum generation by different optical modes in AsSe2-As2S5 chalcogenide microstructured fiber.

We investigate supercontinuum generation (SCG) in AsSe2-As2S5 chalcogenide microstructured optical fibers (MOFs) pumped by different optical modes. The influence on SCG by different optical modes including the fundamental and high-order modes is analyzed numerically. The evolution of the supercontinuum (SC) is investigated by changing the pump wavelength (2120, 2580, and 3280nm) and peak power (from 200 to 1000W) of each optical mode (LP01,LP11,LP31) in the MOFs with different fiber lengths. SCG in MOFs with different core diameters is also simulated. The different optical modes cause the variation of the chromatic dispersion profile and the effective nonlinearity, which induces different mechanisms of the SCG and changes the spectral range. The maximum SC spectral range covers 12.931μm from 1.389 to 14.320μm when pumped by the LP11 mode with the peak power of 1000W at 3280nm. The simulated results will be instructive for the experimental SCG up to the midinfrared waveband longer than 10μm.

Control of Mg2Sn formation through ultrasonic-assisted transient liquid phase bonding of Mg to Al

The formation of Al/Mg intermetallic compounds (IMCs) of Al3Mg2 and Al12Mg17 was successfully avoided through ultrasonic assisted transient liquid phase bonding Mg/Al using pure Sn interlayers. A new IMC of Mg2Sn formed in the joints. Different bonding parameters were used to control the formation of Mg2Sn. The optimum joint shear strength of 60.0 MPa was obtained at the temperature of 220 °C, ultrasonic power of Mode I and ultrasonic time of 4 s. The thickness of Mg2Sn should be depressed to less than 15% of the joint width. Joints were fractured through the Mg2Sn layer.

New method for calculating the coupling coefficient in graded index optical fibers

A simple method is proposed for determining the mode coupling coefficient D in graded index multimode optical fibers. It only requires observation of the output modal power distribution P(m, z) for one fiber length z as the Gaussian launching modal power distribution changes, with the Gaussian input light distribution centered along the graded index optical fiber axis (θ0=0) without radial offset (r0 = 0). A similar method we previously proposed for calculating the coupling coefficient D in a step-index multimode optical fibers where the output angular power distributions P(θ, z) for one fiber length z with the Gaussian input light distribution launched centrally along the step-index optical fiber axis (θ0=0) is needed to be known.

Multi-Point Media Content Sharing Scheme in Internet of Things Networks

Media content sharing scheme among multiple devices is one of the most important service technologies in the Internet of Things (IoT) era. Typically, there are three kinds of schemes adopted for the content sharing among devices: screen mirroring, file casting, and content redirection. Among them, the content redirection in which a sink pulls the content from a cloud server based on universal resource locator information received from a source is a very promising technology in terms of resource usage. However, for the content redirection scheme, the link quality between the access point (AP) and sink must be reliable enough to share the high-quality multimedia services. The link quality problem usually occurs because AP and sink are installed without considering the link quality between the two devices. To solve this problem, in this paper, we introduce a multi-point content delivery scheme, which transfers the media content from both source and AP to sink simultaneously. The proposed scheme can operate in two modes, namely power combining mode that increases the received signal power by combining the transmitted power of both devices and bandwidth aggregation mode that increases the bandwidth of the received signal by aggregating the bandwidth of the transmitted signal of both devices. Numerical results show that using the proposed scheme, with 10 m of AP and sink separation distance, we can get 300% ~ 400% performance improvement; therefore, the proposed scheme can be a core technology for media content sharing in the IoT era.