Modal Power Research Articles

Er-Doped Tapered Fiber Amplifier for High Peak Power Sub-ns Pulse Amplification

A tapered Er-doped fiber amplifier for high peak power pulses amplification has been developed and tested. The core diameter changed from 15.8 µm (mode field diameter (MFD) 14.5 µm) to 93 µm (MFD 40 µm) along 3.7 m maintaining single-mode performance at 1555 nm (according to the S2-method, the part of the power of high-order modes does not exceed 1.5%). The amplification of 0.9 ns pulses with spectral width below 0.04 nm up to a peak power above 200 kW (limited by self-phase modulation) with a slope pump-to-signal conversion efficiency of 15.6% was demonstrated.

Dynamic aerosol and dynamic air-water interface curvature effects on a 2-Gbit/s free-space optical link using orbital-angular-momentum multiplexing.

When an orbital-angular-momentum (OAM) beam propagates through the dynamic air-water interface, the aerosol above the water and the water surface curvature could induce various degradations (e.g., wavefront distortion, beam wandering, scattering, and absorption). Such time-varying degradations could affect the received intensity and phase profiles of the OAM beams, resulting in dynamic modal power loss and modal power coupling. We experimentally investigate the degradation for a single OAM beam under dynamic aerosol, dynamic curvature, and their comprehensive effects. Our results show the following: (i)with the increase of the aerosol strength (characterized by the attenuation coefficient) from ∼0 to ∼0.7-1.3dB/cm over ∼7cm, the power coupling ratio from OAM-1 to +2 increases by 4dB, which might be due to the amplitude and phase distortion caused by spatially dependent scattering and absorption. (ii) With the increase of the curvature strength (characterized by the variance of curvature slope over time) from ∼0 to ∼2×10-5rad2, the power coupling ratio from OAM-1 to +2 increases by 11dB. This could be caused by both the wavefront distortion and the beam wandering. (iii) Under the comprehensive effect of aerosol (∼0.1-0.6dB/cm) and curvature (∼6×10-7rad2), there is an up to 2dB higher modal power loss as compared with the single-effect cases. (iv) The received power on OAM-1 fluctuates in a range of ∼6dB within a 220ms measurement time under aerosol (∼0.1-0.6dB/cm) and curvature (∼6×10-7rad2) effects due to the dynamic degradations. We also demonstrate an OAM-1 and +2 multiplexed 2-Gbit/s on-off-keying link under dynamic aerosol and curvature effects. The results show a power penalty of ∼3dB for the bit-error-rate at the 7% forward-error-correction limit under the comprehensive effect of aerosol (∼0.1-0.6dB/cm) and curvature (∼6×10-7rad2), compared with the no-effect case.

Evaluation of splicing quality in few-mode optical fibers

We propose a method to evaluate the splicing quality for few-mode fibers. A fusion fault detection system for few-mode fiber has been constructed, using OTDR technology, combined with photon lanterns as a multiplexer and a demultiplexer. Every single spatial mode is launched into the few-mode fiber under test through the mode coupler, and the power loss of each mode at the fiber fusion splice is estimated by the Rayleigh backscattering light power of the mixed mode and the single mode. The experimental results indicate that it is necessary to evaluate accurately the splicing quality of a few-mode fiber by all modes that can be transmitted in the fiber under test, rather than by a single mode.

Control as an Enabler for Electrified Mobility

This article outlines the importance of electrified mobility (e-mobility) in modern transport. One key goal of this review is to illustrate the role that control has played, and must continue to play, as e-mobility grows. The coordination of power in multiple modes (mechanical, electrical, and thermal) requires sophisticated controller algorithms. This review advocates for model-based approaches to control since there may not be readily available physical systems from which to gather data and do data-based control. A second goal of the article is to present methods for modeling these powertrain systems that are modular, scalable, flexible, and computationally efficient. A graph-based approach satisfies many of the desired criteria. The third goal is to review control approaches for these classes of systems and detail a hierarchical approach that makes trades across different domains of power. Optimization-based approaches are well suited to achieving the regulation and tracking goals, along with the minimization of costs and the satisfaction of constraints. Multiple examples, within this article and the references therein, support the presentation throughout. This field of e-mobility is rapidly growing, and control engineers are uniquely positioned to have an impact and lead many of the critical developments.

Theory analysis of the optical mode localized sensing based on coupled ring resonators.

Based on Mason's signal flow graph analysis, an analytical model of the optical mode localization based on coupled ring resonators is established. The correctness of the theoretical model is proved by simulation. High sensitivity and common-mode rejection can be achieved by evaluating the modal power ratio from resonant peaks as sensing output. Based on the four-port structure, two output spectrum with mode localization (asymmetric mode splitting) and symmetric mode splitting allows the high-sensitivity sensing and dual-channel calibration to be carried out simultaneously, which can reduce the sensing errors. Monte-Carlo analysis showed that fabrication imperfection changes less than 6% of the performance in 90% cases, thus the construction of practical sensors is possible with appropriate tuning. The optical mode localized sensing has advantages in sensitivity, accuracy, anti-aliasing compared with conventional micro-mechanical mode localized sensor. Various types of high-sensitive sensor can be constructed through coupling parametric perturbation with measurands in different physical domains.

Ultrasensitive polyaniline‐nickel oxide cladding modified with urease immobilized intrinsic optical fiber urea biosensor

AbstractHerein, we report a polyaniline‐nickel oxide (PANI‐NiO) nanocomposite as an efficient immobilization matrix for development the optical fiber urea biosensor. Optical fiber sensing probe was developed by removing some portion of optical fiber at middle and modified with PANI‐NiO matrix. After the modification of cladding removed portion, it was immobilized with enzyme urease via glutaraldehyde as a bi‐functional cross‐linking agent. The physicochemical and optical properties of the PANI‐NiO matrix were explored by X‐ray diffraction, scanning electron microscopy, ultraviolet–visible, and Fourier transform infrared spectroscopic techniques. The characteristic features and performance of the developed sensor were evaluated via recording the output power and modal power distribution by means of a charge‐coupled device camera. The developed urea biosensor exhibits a selective response towards urea concentrations in the linear range 1 nM–100 mM with a lower detection limit of 1 nM. Sensor recorded as a 40 days stability and response time ~1 min. Thus, the obtained experimental results of the developed sensor promote its applicability with practical prospects in diverse field.

Research on Improving Flexibility of Thermal Power Units by Flue Gas-water Heat Exchanger

The proportion of renewable energy in the power supply structure of Shandong power grid is increasing day by day. Thermal power units inevitably face deep-peak shaving and frequent-peak shaving. The problem of thermal power contradiction is prominent when thermal power units are heating in winter, which has a negative impact on the security and stability of power grid and the consumption of renewable energy. Traditional thermoelectric decoupling technology has some problems such as narrow load adjustment range and poor overall energy utilization efficiency. A scheme of adding flue gas-water heat exchanger is proposed to supplement the traditional IP cylinder extraction technology for heating. According to the calculation, the minimum electric power of flue gas heating mode is significantly lower than that of traditional heating mode under small heating demand, and the maximum and minimum electric power of hybrid heating mode are better than that of traditional heating mode under the same heating demand, and the maximum heating capacity under the mixed heating mode is significantly increased, which can improve the operation flexibility of the unit and enhance the thermoelectric decoupling ability of the unit.

Power Response and Modal Decay Estimation of Room Reflections from Spherical Microphone Array Measurements Using Eigenbeam Spatial Correlation Model

Modal decays and modal power distribution in acoustic environments are key factors in deciding the perceptual quality and performance accuracy of audio applications. This paper presents the application of the eigenbeam spatial correlation method in estimating the time-frequency-dependent directional reflection powers and modal decay times. The experimental results evaluate the application of the proposed technique for two rooms with distinct environments using their room impulse response (RIR) measurements recorded by a spherical microphone array. The paper discusses the classical concepts behind room mode distribution and the reasons behind their complex behavior in real environments. The time-frequency spectrum of room reflections, the dominant reflection locations, and the directional decay rates emulate a realistic response with respect to the theoretical expectations. The experimental observations prove that our model is a promising tool in characterizing early and late reflections, which will be beneficial in controlling the perceptual factors of room acoustics.

Study on heating performance of solar-assisted heat pump drying system under large temperature difference

In this study, a heat pump drying (HPD) system platform complemented by solar hot water was designed and established. The objective was to address the declines in the heating performance of air source HPD at high altitudes (more than 3000 m), cold conditions (annual average temperature at 5 °C), and with large temperature differences between day and night (more than 20 °C), i.e. under harsh conditions. A theoretical model was derived to determine the system parameters and to support the experimental analysis. Under no-load conditions, four cases with ambient temperature were tested and compared to explore the relationships between the system parameters and performance, as well as the effectiveness of the supplementary solar hot water. The heating performances under HPD and solar-assisted HPD (SHPD) modes were compared and analysed under load conditions (930 kg Mu Xiang). The results indicate that a decrease in the ambient temperature and increase in the temperature in the drying room causes attenuations of the compressor mass flow rate, evaporator cooling power, condenser heating power, and system coefficient of performance (COP). In addition, solar water heating can significantly improve the heating performance of the HPD system. Under no-load conditions, the average heating power of the HPD-mode system is 19.27 kW, and the average COP is 2.76. The average heating power of the SHPD mode system is 23.34 kW, and the average COP of the system reaches 3.24, an increase of 17.4%. Under load conditions, the average heating capacity power of the HPD mode is 9.64 kW; the COP is only 1.34, and fluctuates significantly with the decrease in ambient temperature. The average heating capacity power of the SHPD mode is 17.62 kW and the COP is 2.42, i.e. 1.8 times of that of the HPD mode. By raising the drying room temperature to the same set temperature, the SHPD mode time is shortened by 70%.

Artificial Intelligence-Based Optimization of a Bimorph-Segmented Tapered Piezoelectric MEMS Energy Harvester for Multimode Operation

This paper presents a study on the design and multiobjective optimization of a bimorph-segmented linearly tapered piezoelectric harvester for low-frequency and multimode vibration energy harvesting. The procedure starts with a significant number of FEM simulations of the structure with different geometric dimensions—length, width, and tapering ratio. The datasets train the artificial neural network (ANN) that provides the fitting function to be modified and used in algorithms for optimization, aiming to achieve minimal resonant frequency and maximal generated power. Levenberg–Marquardt (LM) and scaled conjugate gradient (SCG) methods were used to train the ANN, then the goal attainment method (GAM) and genetic algorithm (GA) were used for optimization. The dominant solution resulted from optimization by the genetic algorithm integrated with the ANN fitting function obtained by the SCG training method. The optimal piezoelectric harvester is 121.3 mm long and 71.56 mm wide and has a taper ratio of 0.7682. It ensures over five times greater output power at frequencies below 200 Hz, which benefits the low frequency of the vibration spectrum. The optimized design can harness the power of higher-resonance modes for multimode applications.

Identifying Acoustic Wave Sources on the Sun. I. Two-dimensional Waves in a Simulated Photosphere

Abstract The solar acoustic oscillations are likely stochastically excited by convective dynamics in the solar photosphere, though few direct observations of individual source events have been made and their detailed characteristics are still unknown. Wave source identification requires measurements that can reliably discriminate the local wave signal from the background convective motions and resonant modal power. This is quite challenging as these noise contributions have amplitudes several orders of magnitude greater than the sources and the propagating wave fields they induce. In this paper, we employ a high-temporal-frequency filter to identify sites of acoustic emission in a radiative magnetohydrodynamic simulation. The properties of the filter were determined from a convolutional neural network trained to identify the two-dimensional acoustic Green’s function response of the atmosphere, but once defined, it can be directly applied to an image time series to extract the signal of local wave excitation, bypassing the need for the original neural network. Using the filter developed, we have uncovered previously unknown properties of the acoustic emission process. In the simulation, acoustic events are found to be clustered at mesogranular scales, with peak emission quite deep, about 500 km below the photosphere, and sites of very strong emission can result from the interaction of two supersonic downflows that merge at that depth. We suggest that the method developed, when applied to high-resolution high-cadence observations, such as those forthcoming with the Daniel K. Inouye Solar Telescope, will have important applications in chromospheric wave studies and may lead to new investigations in high-resolution local helioseismology.

Numerical and experimental study of a multimode optical fiber sensor based on Fresnel reflection at the fiber tip for refractive index measurement

This paper presents the numerical and experimental study of a multimode optical fiber (MMF) sensor based on Fresnel reflection at the fiber tip. Considering different modal power distributions (uniform mode distribution, gaussian and equilibrium mode distribution), the effective fraction of the incident light reflected at the interface between the end of the fiber and the surrounding medium is first calculated numerically with a ray model. Even when considering modal power distribution and non-normal incidence influence, simplifying assumptions such as normal incidence hypothesis can be made to facilitate experimental data exploitation, with a maximum error on the deduced medium refractive index of the 10-4 order. A statistical analysis of noise is then made, to study the influence of a random noise between 0.1% and 5% noise level: results show that the approximation error made by using normal incidence formula for a Fresnel sensor based on a MMF is significantly smaller than the repeatability error. These assumptions are then verified experimentally with two experimental setups by measuring the refractive index at 1550 nm of reference solutions (distilled water-isopropanol and distilled water-sodium chloride mixtures) with a Fresnel based on a multimode fiber, and a Fresnel based on single-mode fiber for comparison. Good agreement is found with refractive index values from the literature with a maximum relative difference of only 0.1%, and the maximum experimental uncertainties in this work is 1.1×10-4. Differences between refractive index measured with a Fresnel based on single-mode and multimode fiber are found to be in accordance with values from the statistical study.

Sympathetic Vampires and Zombies with Brains: The Modern Monster as a Master of Self‐Control

Sympathetic Vampires and Zombies with Brains: The Modern Monster as a Master of Self‐Control

Absorption of High-frequency Oscillations and Its Relation to Emissivity Reduction

Abstract Sunspots are known to be strong absorbers of solar oscillation modal power. The most convincing way to demonstrate this is done via Fourier–Hankel decomposition (FHD), where the local oscillation field is separated into in- and outgoing waves, showing the reduction in power. Due to the Helioseismic and Magnetic Imager’s high-cadence Doppler measurements, power absorption can be investigated at frequencies beyond the acoustic cutoff frequency. We perform an FHD on five sunspot regions and two quiet-Sun control regions and study the resulting absorption spectra α ℓ (ν), specifically at frequencies ν > 5.3 mHz. We observe an unreported high-frequency absorption feature, which only appears in the presence of a sunspot. This feature is confined to phase speeds of one-skip waves whose origins coincide with the sunspot’s center, with v ph = 85.7 km s−1 in this case. By employing a fit to the absorption spectra at a constant phase speed, we find that the peak absorption strength lies between 0.166 and 0.222 at a noise level of about 0.009 (5%). The well-known absorption along ridges at lower frequencies can reach up to . Thus our finding in the absorption spectrum is weaker, but nevertheless significant. From first considerations regarding the energy budget of high-frequency waves, this observation can likely be explained by the reduction of emissivity within the sunspot. We derive a simple relation between emissivity and absorption. We conclude that sunspots yield a wave power absorption signature (for certain phase speeds only), which may help in understanding the effect of strong magnetic fields on convection and source excitation and potentially in understanding the general sunspot subsurface structure.

Numerical investigation on Ge2Sb2Te5-assisted reconfigurable asymmetric directional coupler-based switches

The performance analysis on phase change material germanium-antimony-tellurium-Ge2Sb2Te5 (GST)-assisted silicon waveguide-based non-volatile 1 × 2 and 2 × 2 switches are proposed. The designed structure contains a hybrid silicon waveguide and a regular silicon waveguide. By perfectly choosing the design considerations of the proposed switches, the power of transverse electric mode is coupled and shifted to cross port as an output at the amorphous state of GST (aGST), and for the crystalline state of GST (cGST), the input mode passes through the bar port as an output. The performances of the switches are evaluated by numerical calculations with the help of mode analysis of 2D finite-element method (FEM), and it is further verified by 3D finite-difference time-domain method (FDTD). For the 1 × 2 and 2 × 2 proposed switches, the obtained insertion loss (IL) of both phases of GST is <1 dB. For 1 × 2 switch design, the calculated cross-talk (CT) and extinction ratio (ER) are −31.32 and 31.31 dB, respectively at aGST state and for the cGST state, the values of CT and ER are −20.77 and 20.73 dB at 1550-nm operating wavelength. Similarly, for 2 × 2 switch design, the observed CT and ER are −32.7 and 32.69 dB, correspondingly at aGST state and for the cGST state; they are −11.98 and 11.71 dB, respectively. An additional optimization is realized via variations in the wavelength, GST width, and the coupling gap with the help of FEM analysis. Hence, broadband (80 nm) and ultracompact (∼20 μm) switches are proposed with low IL, high ER, and low CT, which can be suitable for reconfigurable optical interconnects, optical field-programmable gate array applications, microwave photonics, and quantum computing.

Investigation on Speckle-Free Imaging at the Output of a Multimode Fiber under Various Mode Excitation Conditions

Speckle-free imaging using a multimode fiber has been widely used for imaging systems. Generally, previous work has assumed that all the propagating modes of the fiber are uniformly excited, but the modal power distribution is actually affected by excitation conditions. Here, we propose the utilization of a modal analysis method to study the dependence of the speckle contrast on the modal power distribution by changing the tilt angle of the Gaussian beam and on the group delay time difference caused by different fiber lengths. The results of numerical simulations and experiments show that, with an increase in the tilt angle of the Gaussian beam, the modal power is transferred to higher-order modes and the maximum delay difference between excitation modes becomes larger. Therefore, the inter-mode interference effect is effectively weakened, and the speckle contrast is significantly reduced. The increase in fiber length will also make the delay difference between excitation modes larger and thus the speckle contrast is decreased. For the larger tilt angle of the Gaussian beam, only a shorter optical fiber is required to reduce the speckle contrast significantly. Our work further promotes the use of a multimode fiber to produce speckle-free patterns in laser imaging systems.

Multi-input and multi-output bi-directional power converter for solar photovoltaic system

This paper presents the development of a multi-input multi-output bi-directional power converter (MIMO-BDPC) with a digital pulse-width modulation (DPWM) controller for solar photovoltaic (SVP) application. The converter is operated in three modes such as buck, boost, and inverter. The converter uses a minimum number of active components and the DPWM controller controls the switching frequency or pulse period which are reconfigurable for effective synchronous and autonomous operation. The autonomous mode is selected by the controller based on the availability of the power source. The combination of high performance, low cost, and high reliability in a single controller is achieved via this intelligent digital approach. The controller is based on the power and load changes in multiple PWM modes. The Intel Altera Cyclone IV FPGA control will be used for digital PWM. The FPGA is scheduled for parallel data processing with multiple resource blocks. During control, this controller can be reprogrammed dynamically again. This makes the system extremely efficient in the check aspect, reducing time and cost. The proposed MIMO-BDPC is tested with the above-mentioned modes of operation using MATLAB software and also through hardware results.

Design of Step-Index Multimode Optical Fiber

In this paper, a step-index fiber with core index 1.445 5 1 7 and cladding index 1.443 1 5 7 has been designed and studied. Multimode operation is achieved by using a fiber with core radius 25 μm operating at a wavelength of 1.3 μm. The mode parameters (effective refractive index, phase constant, fractional modal power in the core and cutoff wavelength) were calculated using RP fiber calculator (PRO version 2020). The shapes of the intensity and amplitude distribution of linearly polarized guided modes were shown.

Towards lab-on-chip ultrasensitive ethanol detection using photonic crystal waveguide operating in the mid-infrared

Abstract Thanks to the unique molecular fingerprints in the mid-infrared spectral region, absorption spectroscopy in this regime has attracted widespread attention in recent years. Contrary to commercially available infrared spectrometers, which are limited by being bulky and cost-intensive, laboratory-on-chip infrared spectrometers can offer sensor advancements including raw sensing performance in addition to utilization such as enhanced portability. Several platforms have been proposed in the past for on-chip ethanol detection. However, selective sensing with high sensitivity at room temperature has remained a challenge. Here, we experimentally demonstrate an on-chip ethyl alcohol sensor based on a holey photonic crystal waveguide on silicon on insulator-based photonics sensing platform offering an enhanced photoabsorption thus improving sensitivity. This is achieved by designing and engineering an optical slow-light mode with a high group-index of n g = 73 and a strong localization of the modal power in analyte, enabled by the photonic crystal waveguide structure. This approach includes a codesign paradigm that uniquely features an increased effective path length traversed by the guided wave through the to-be-sensed gas analyte. This PIC-based lab-on-chip sensor is exemplary, spectrally designed to operate at the center wavelength of 3.4 μm to match the peak absorbance for ethanol. However, the slow-light enhancement concept is universal offering to cover a wide design-window and spectral ranges towards sensing a plurality of gas species. Using the holey photonic crystal waveguide, we demonstrate the capability of achieving parts per billion levels of gas detection precision. High sensitivity combined with tailorable spectral range along with a compact form-factor enables a new class of portable photonic sensor platforms when integrated with quantum cascade laser and detectors.

An energy efficient electric drive of air units

Purpose. Improving the efficiency and energy performance of an asynchronous electric drive for stationary fan’s units of the main ventilation line of mines.&#x0D; Methodology. The research was carried out using the methods of the theory of electrical circuits, mathematical physics, simulation, interpolation and approximation&#x0D; Findings. The research of electromagnetic and energy processes in the asynchronous electric drive system with pulse control at a fan load, taking into account the variable aerodynamic parameters of the main ventilation line of mines. An electric drive system is able to respond with high accuracy and reliability to changes in the aerodynamic parameters of the main ventilation line of mines has been proven. This will also increase the power factor of the electric drive at a fan load up 0.8 to 0.93 p.u., and the efficiency up 92.5% to 94.5%, when regulating in the range of the operating slip of the rotor of the drive fan motor = 0.5 ÷, which, respectively, is on average up 0,25% to 40 higher in comparison with systems of an unregulated electric drive. Recommendations has been developed for the design and rational selection of the rated fan capacity for the main ventilation line to advance the best energy efficiency level of the electric drive.&#x0D; Originality. The research of electro-mechanical, electro-energy power and aerodynamic processes in the dynamic modes of the fan electric drive was carried out. The fan-loaded "induction motor-converter" system has been proven to be self-regulating. It is able to respond with high accuracy and reliability even at low switching frequencies of the power chopper to any changes of the aerodynamic parameters of the main ventilation line of mines.&#x0D; Practical value. Recommendations has been developed for the design and rational selection of the rated fan capacity for the main ventilation line to advance the best energy efficiency level of the electric drive.