Frequency Conversion Research Articles

Improving the operational characteristics of electrical power systems of marine vessels

THE PURPOSE. Consider the experience of use and conduct a study of the electrical power systems of sea vessels to determine the possibility of improving their operational characteristics. Obtain data on noise and vibration levels of electrical power systems elements.METHODS. The article analyzes the electrical power systems of the Azipod type steering columns of the Baltika icebreaker. The issue of regulating the rotation speed of propulsion electric motors using frequency control based on a DC link and parallel-connected inverter units on IGBT transistors is considered. Motor control on the frequency converter side can be based on direct torque control, scalar and vector control. There are control modes for reducing and increasing voltage.RESULTS. Typical dependences of structure-borne noise levels of main engines and generators are given. Measurements were taken at various frequencies of engine sound power levels, exhaust gases and vibration of generator sets. Experimental oscillograms of studies of the parallel operation of diesel generator sets were obtained, on which power exchange and common-mode oscillations were recorded.CONCLUSION. It is proposed to use multiphase AC electric motors to improve performance characteristics, including reducing noise and vibration. The existing experience in using frequency converters based on a rectifier section and inverter units in electric rowing installations with Azipod propellers makes it possible to implement such a change. To do this, it is necessary to parallelize the inverters that supply each of the three phases and provide the appropriate phase shifts.

Enhanced terahertz third-harmonic generation based on the graphene-assisted meta-grating structure

The nonlinear response of optical materials provides a valuable approach for optical switching and nonlinear frequency conversion. However, the nonlinear responses of bulk crystals are often very weak, requiring higher pump energy for pumping. In this work, we investigate the significant enhancement of third harmonic generation (THG) at terahertz frequencies using an ultra-thin nonlinear meta-grating metasurface assisted by graphene strips. In this structure, the incident pump light experiences strong confinement and enhancement along the graphene surface caused by the generation of strongly localized surface plasmon resonances. Utilizing the significant third-order nonlinear conductivity of graphene, it becomes possible to achieve high THG conversion efficiency even at low pump intensities. The research results indicate that, at low incident intensity of 10 kW/cm2, the third harmonic wave conversion efficiency can reach approximately 2.8 %. We also thoroughly investigate the impact of meta-grating structural parameters, graphene Fermi level, incident angle, and pump light intensity on THG operation characteristics. Our study findings provide an effective approach for greatly boosting the THG conversion efficiency in the terahertz frequency bands, opening new avenues in the development of novel compact frequency converters and modulators that are emerging in terahertz chip integration and nonlinear devices.

Intelligent pressure switching control method for air compressor group control based on multi-agent reinforcement learning

In order to effectively control the pressure and energy consumption of multiple air compressors within an acceptable range, an intelligent pressure switching control method for air compressor group control based on multi-agent RL is studied. This method uses sensors in the air compressor field control cabinet to collect data such as header pressure, air storage tank pressure, and air storage tank temperature and sends them to the edge data collector for integration. After integration, the main control cabinet sends them to the upper computer. Combined with the on-site collected data, a multi-agent-based air compressor group control model is designed to convert multiple air compressors in the air compressor group control problem into a multi-agent mode, facilitating unified switching control of the air compressor group. Then, using the intelligent pressure switching control method based on deep Q-learning, driven by a neural network controller, the frequency of the frequency converter is adjusted to control the pressure at the outlet of the air compressor terminal header within the set value range, completing the pressure intelligent switching control. After testing, this method has good application results in pressure control, energy saving, and other aspects after being used for intelligent pressure switching control of air compressor group control.

Comments on “Growth dynamics and molecular structural analysis of dimethylketo thiosemicarbazone single crystals for frequency conversion applications–Optical and thermal characterization”

The authors of the title paper (J Mol Struc1239 (2021) 130463) report to have synthesized for the first time dimethylketo thiosemicarbazone (DMKT) and determined its single crystal structure. In contrast to this claim, the so-called DMKT is not a new organic Schiff base, but in fact, the commercially available acetone thiosemicarbazone, whose single crystal structure reported in 1974, is archived in the Cambridge Structural Database (CSD). In this letter to the Editor, we highlight the importance of compound nomenclature as well as deposition of single crystal structure data in the CSD by taking DMKT as an example.

Telecom Networking with a Diamond Quantum Memory

Practical quantum networks require interfacing quantum memories with existing channels and systems that operate in the telecom band. Here we demonstrate low-noise, bidirectional quantum frequency conversion that enables a solid-state quantum memory to directly interface with telecom-band systems. In particular, we demonstrate conversion of visible-band single photons emitted from a silicon-vacancy (SiV) center in diamond to the telecom O band, maintaining low noise (g2(0)<0.1) and high indistinguishability (V=89±8%). We further demonstrate the utility of this system for quantum networking by converting telecom-band time-bin pulses, sent across a lossy and noisy 50-km deployed fiber link, to the visible band and entangling them with a diamond quantum memory with fidelity F≥87±2.5%. These results demonstrate the viability of SiV quantum memories integrated with telecom-band systems for scalable quantum networking applications. Published by the American Physical Society 2024

High-voltage DC–DC converter based on adaptive frequency conversion modulation

High-voltage DC–DC converter based on adaptive frequency conversion modulation

High-efficiency second harmonic generation in a micro-resonator on dual-layered lithium niobate.

High-quality micro-resonators on thin-film lithium niobate (TFLN) have emerged as an ideal platform for on-chip nonlinear optical applications due to their strong light confinement and excellent natural nonlinear optical properties. Here, we present high-efficiency second-harmonic generation (SHG) in micro-resonators on a TFLN based on the modal phase matching and natural quasi-phase matching. By optimizing the phase-matching conditions through thermal tuning, we demonstrate an on-chip SHG efficiency of 149,000%/W in the low power regime. Furthermore, we achieve an absolute conversion efficiency of 10.3% with a 0.3 mW pump power. Our work paves the way toward future efficient on-chip frequency conversion of classical and quantum light without the need for poling of the LN films.

Obtaining constant sub-25 ns pulse in a Q-switched Tm laser with around 100 kHz repetition frequency

Conventionally, pulse duration of Q-switched lasers changes dynamically with the lasing power and pulse repetition frequency (PRF). Especially in quasi-three level Tm lasers, owing to the small emission cross section, they should oscillate at a PRF of below 50 kHz for a short Q-switching pulse that generally limited at tens of nanosecond. In this paper, we demonstrate an unprecedented electro-optically Q-switching scheme with constant short pulse duration of sub-25 ns at high PRFs ranging from 75 kHz to 150 kHz. Maximum average output power of 22.4 W at 1936.8 nm is obtained at 75 kHz, where average pulse duration of 21 ns with a deviation below 0.8 ns is realized during the whole Q-switching process, corresponding to a maximum peak power of 14.2 kW. The results provide an efficient way to achieve constant short nanosecond pulse in the high-power Q-switched Tm lasers, which could work at a PRF of above 100 kHz and facilitate a variety of appealing applications in material processing, surgery, and nonlinear frequency conversion toward the mid- and far-infrared regions.

Nonreciprocal propagation of bending waves in spatiotemporally modulated prestressed beam

Breaking time or/and spatial symmetry can lead to unprecedent mechanical responses of a structure, the design of which is usually very intricate. This paper proposes a simple design of a beam structure with spatiotemporal modulation. In fact, a time-varying axial load applied to the ends of an elastic beam will induce space-time dependent axial force propagating in the form of longitudinal wave in the beam, which can modulate spatiotemporally the propagation of transverse bending waves. The governing equation is derived, of which the Floquet solution leads to a quadratic eigenvalue problem that can be solved for the frequency as a function of the wavenumber. Theoretical results show the existence of asymmetric wavenumber bandgaps and the unique dispersion diagram which is not periodic with respect to time or space. The breaking of temporal symmetry enables nonreciprocal propagation of transverse bending waves, which is confirmed by the finite element simulations. This modulation method offers promise for applications in the fields of elastic wave filter, frequency converter and magnitude amplifier.

Low-repetition-rate optical frequency comb

Reducing the pulse repetition rate of an optical frequency comb increases the pulse energy for a given average power. This enhances the efficiency of nonlinear frequency conversion and it facilitates extending the accessible wavelength range, for example, into the extreme ultraviolet (XUV). The resulting spectrally dense frequency comb can still be used for precision spectroscopy of narrow atomic or molecular transitions. In this paper, we demonstrate a low-noise infrared frequency comb with a repetition rate as low as 40 kHz using a Yb:KYW mode-locked laser, pulse picking, and subsequent amplification. The frequency comb structure is confirmed by generating a beat note with a continuous wave reference laser. A comb mode is actively stabilized to the reference laser, and the integrated rms phase noise from 20 Hz to 20 kHz is measured to be 195 mrad.

Linear-frequency conversion with time-varying metasurfaces

Frequency conversion is a hallmark of nonlinearity. The spectral manifestations, emergent within a system, can typically be attributed to a marked nonlinearity within the material properties, complex geometric configurations, and/or the unique functional form of interactions taking place in the constitutive subsystems. These phenomena, irrespective of their origins, have been harnessed and exploited in applications ranging from the generation of entangled photons, a cornerstone in quantum technologies, to nanomechanical frequency mixing, advancing subsurface scanning probe microscopy. Here, we propose a frequency conversion mechanism based on time-varying metasurfaces, an emerging frontier in metamaterial research. We show how temporal properties of metasurfaces can effectively emulate a nonlinear medium, thereby facilitating frequency conversion. The proposed material configuration has the potential not only to advance integrated photonics and quantum optics, but also to create opportunities in quantum sensing, quantum materials, and crucially quantum communications. Published by the American Physical Society 2024

Enhancing second harmonic generation by Q-boosting lossless cavities beyond the time bandwidth limit

Abstract Nanostructures proved to be versatile platforms to control the electromagnetic field at subwavelength scale. Indeed, high-quality-factors nanocavities have been used to boost and control nonlinear frequency generation by increasing the light–matter interaction. However, nonlinear processes are triggered by high-intensities, which are provided by ultrashort laser pulses with large bandwidth, which cannot be fully exploited in such devices. Time-varying optical systems allow one to overcome the time-bandwidth limit by modulating the cavity external coupling. Here we present a general treatment, based on coupled mode theory, to describe second harmonic generation in a doubly resonant cavity for which the quality-factor at the fundamental frequency is modulated in time. We identify the initial quality factor maximizing second harmonic efficiency when performing Q-boosting and we predict a theoretical energy conversion efficiency close to unity. Our results have direct impact on the design of next generation time-dependent metasurfaces to boost nonlinear frequency conversion of ultrashort laser pulses.

Reducing reactive energy consumption by optimizing operating modes of irrigation pumping stations

The article develops energy and resource efficiency modes of the technological process that meet the requirements of the “frequency converter - asynchronous motor - pump - pressure pipeline” system as a control object. Methods for regulating water pressure and water flow produced by pumping units are considered in order to ensure a schedule for water supply to irrigation pumping stations. The active, reactive and total electrical energies received by an asynchronous motor to change water flow by changing the position of the pressure valve in the pressure pipeline are calculated. In order to optimize water flow and water pressure by changing the speed of rotation of the pump impeller, the frequency converter system of an asynchronous motor with a squirrel-cage rotor was calculated and compared with the method of changing water flow using a push valve, by calculating active, reactive and total electrical energy from the network.

509 nm high power wide-tuned external cavity surface emitting laser

High power widely tunable green lasers have potential applications in many fields such as biomedicine, lidar, laser spectroscopy, laser display, underwater wireless optical communication, and fine processing of nonferrous metals. Vertical-external-cavity surface-emitting lasers, also known as semiconductor disk lasers, have the advantages of high power, good beam quality, and wide bandwidth of gain medium. In this work, a gain chip with a reverse-growth epitaxy structure and an emitting wavelength of 1018 nm is designed. In the DBR reflection spectrum, a bandwidth of 74 nm is achieved above a reflectivity of greater than 99.1%, laying a solid foundation for achieving high-power widely tunable output. The laser cavity combines a 1018 nm semiconductor gain chip, a folded mirror, and a plane mirror to construct a compact V-type resonant cavity. A class-I phase-matched LBO nonlinear crystal with a length of 10 mm is placed at the beam waist of the cavity to realize an efficient frequency doubling process to produce a 509 nm green laser. To meet the requirement for the polarization during frequency conversion and to tune the oscillating wavelength of the laser, a birefringent filter (BRF) is employed in the laser resonant cavity. When the thickness of the used BRF is 1 mm, the obtained wavelength tuning range of the fundamental laser and the frequency doubled green laser are 47.1 nm and 20.1 nm, respectively, showing a good tuning capability of the laser. The laser’s performance varies with the thickness of the BRF. When using a 2 mm BRF, a maximum power output of the frequency-doubled green laser reaches 8.23 W during continuous tuning, indicating an ideal compatibility of wide tuning characteristics with a high power output. Meanwhile, its beam quality <i>M</i> <sup>2</sup> factors are 1.00 and 1.03 in the <i>x</i>- and <i>y</i>-direction, respectively, demonstrating a near diffraction-limited excellent beam quality. This green laser also possesses a frequency doubling conversion efficiency of up to 68.2%, which can efficiently converse the fundamental laser into the frequency doubled green laser. The optical-to-optical conversion efficiency from the absorbed pump light to the frequency-doubled green light also reaches 16.6%. Meanwhile, from the spectral linewidths of the green lasers under different thickness values of BRFs it is found that the thicker the BRF, the narrower the laser line width is, which is consistent with the theoretical result.

Effect of deuterium content on the structural, optical, and thermal properties of DKDP crystals: a systematic analysis.

Deuterated potassium dihydrogen phosphate (DKDP) crystals with different deuterium contents have a wide range of applications, such as frequency conversion in high power lasers, electro-optic modulation, and Q-switching crystals for Pockels cells. However, there is a lack of systematic research on the effect of deuterium content on the fundamental structure and properties of these DKDP crystals. To this end, in this study, a series of DKDP crystals with different deuterium contents have been grown using the "point-seed" rapid growth method, and the structure and properties of the crystals have been characterized. The results indicate that as the deuterium content increases, the cell parameter along the a(b)-axis direction gradually increases, and the transmittance gradually increases in the infrared range. A small amount of doping (low H or D ratio) reduces the structural integrity of the crystal, and the crystals at intermediate deuterium concentrations have better crystallinity. The thermal properties of the crystals do no change significantly with the variation in the deuterium content. Overall, these findings can serve as a useful reference for boosting the application of DKDP crystals with various deuterium contents.

Ultrabroadband nonlinear enhancement of mid-infrared frequency upconversion in hyperbolic metamaterials.

Metamaterials have demonstrated significant potential for enhancing nonlinear processes at the nanoscale. The presence of narrowband hot-spots and highly inhomogeneous mode-field distributions often limit the enhancement of nonlinear interactions over larger spatial scales. This has posed a formidable challenge in achieving simultaneous enhancement across a broadband spectral range, significantly constraining the potential of photonic nanostructures in enhancing nonlinear frequency conversion. Here, we propose a broadband resonant mode matching method through near-field examinations that supports the multipole modes and enables the development of an ultrabroadband-enhanced 3-5 μm mid-infrared frequency upconversion technique utilizing a hyperbolic triangular pyramidal metasurface. The gap-plasma mode of the hyperbolic metamaterial multilayer system excites narrowly high-order resonances at near-infrared pump light wavelengths, while the slow-light effect generated by the dipoles achieves ultrabroadband near-field enhancement at mid-infrared wavelengths. The symmetry breaking of the triangular structure localizes these resonant modes at the tips, enabling mode-matched modulation at different wavelengths, and thus boosting the nonlinear frequency conversion process. Our approach provides a promising platform for metasurface-based frequency conversion techniques.

Excited state dependent fast switching NLO behavior investigation of sp2 hybridized donor crystal as D-π-A push–pull switches

This research focused on the investigating electronic and optical properties of designed chromophores (TPTP1-TPTP5) to involve their comprehensive analysis, including geometry optimization, UV–Vis spectroscopy, analysis of the transition density matrix (TDM), and exploration of their nonlinear optical (NLO) responses. The chromophore TPTP1 and TPTP2 exhibit significant transitions, making them suitable for optical switching applications. The chromophore TPTP5 stood out with high values for linear polarizability (<α0>, 8.53 × 10-24 esu), first order polarizability β0 (3.86 × 10-24 esu), and second order hyperpolarizability (γ0, 6.41 × 10-24 esu), making it notable for its nonlinear optical response. A positive correlation was observed between their vertical ionization potential (VIP) and the γ0 related NLO response, indicating that higher VIP values correspond to stronger γ0 responses. Their UV–Vis spectroscopy was employed to examine the absorption properties of the chromophores, revealing the wavelengths (λmax) at which they absorbed light and their potential for light harvesting applications. The analysis of the TDM allowed for a deeper understanding of the redistribution of electron density during electronic transitions within the chromophores. This analysis provided valuable insights into the characteristics and nature of their excited states. Additionally, the research investigated the NLO responses of the chromophores, particularly focusing on their third harmonic generation (THG) properties. These NLO properties are crucial for potential applications in optical switches, frequency conversion, and optical signal processing. Overall, the findings from this research contribute to a comprehensive understanding of the electronic and optical properties of the designed chromophores. The obtained results open up new possibilities for their utilization in various technological fields, including light harvesting, photonics, and nonlinear optics.

Variation of air condition parameters, in the conditions of the presence of carbon dioxide, in the duct of ventilation installations

Industrial ventilation takes into account the quality of the air inside the IAQ (Indoor Air Quality) and the degree of exposure of workers. In industrial targets the emission regime of contaminants can be 10–100 times higher than in non-industrial targets, but for many pollutants the IAQ levels can be the same. The parameters of the state of the air which are of interest for the technique of ventilation and air conditioning are: air temperature and humidity, atmospheric pressure and air speed. For the study on the variation of the air state parameters inside the industrial ventilation installations, in the experiment laboratory, on the study of the industrial ventilation systems, the experiment was performed on the variation of the air state parameters in the conditions of circulation through the ventilation duct. an amount of carbon dioxide. Prior to the introduction of carbon dioxide into the duct, the ventilation system was started, at nominal parameters. During the experiment, the operating parameters of the drive motor were changed using a frequency converter on levels 50; 40; 30; 20; 10 and 5 Hz. The ventilation system used was structured by means of flow converters which were fixed in the open position. The ventilation system as well as the flow variators were operated by the SCADA type command and control system The paper will present the analysis of the variation of state parameters (temperature, humidity, absolute pressure and air speed) by introducing a constant amount of carbon dioxide in the ventilation duct.

Increasing efficiency of induction motor by predictive control system

Standard squirrel-cage induction machine is widely used in industrial enterprises due to its advantages in terms of reliability, durability and economic efficiency. However, one of its disadvantages is that it suffers from a power dissipation factor due to its inability to balance active and reactive power consumption. Especially when the SCIM is running at no load condition or during the initial start-up, the power factor or useful operation and performance are drastically reduced. Therefore, improving the power factor of the induction machine is an actual topic for the following article, and has had some interesting solutions for several years. In this thesis, two different induction motor control algorithms (frequency converter and Predictive torque control) are included and a clear comparison between them is given. The main focus of this article is to design an induction motor control system using the two algorithms mentioned above, analyse the performance of different control methods, and experimentally verify these algorithms by comparing simulations and experimental results.

Energy saving using a frequency converter in asynchronous motor operating modes

This scientific article discusses asynchronous motors using single-season and multi-season sizes, their optimized modes for scalar and vector control. First of all, detailed information was given about the operating modes of the optimizer, followed by changes in voltage, magnetic current and electric current. With scalar control, mode optimizers are optimized for maximum and minimum electric current, while with vector control, optimization is achieved through direct or indirect action on the rotor. Based on the above, complex optimization methods are considered in detail and graphs from their mathematical model are presented. In this case, the conditional minima of the electric current in the lower region and the local minima of the electric current in the lower region are shown on the graphs. The data obtained were compared with complex optimization and extraterrestrial characteristics. As a result of the article, the mentioned methods proposed a scheme of the final optimization structure and a system of equations that mathematically represent them all. The results obtained showed that even with the help of a simple circuit, optimal control of asynchronous motors can be achieved with good results when using optimizers of complex modes, rather than scalar or vector current control. In the future, the control of this method will become the basis for solving energy-saving problems achieved through the use in asynchronous motors with a short-circuited rotor, which are regulated by a frequency switch located in pumping plants of industrial enterprises.