Frequency Conversion Research Articles

Divergent beam-based method for measuring the detuning angles of a laser frequency converter.

We propose a method to obtain the detuning angles of a frequency converter by tripling the frequency of a divergent Gaussian beam. The frequency tripling process of the divergent beam was first simulated. It is found that the detuning angles of the frequency converter are linearly related to the position of the maximum light intensity point of the third harmonic laser. The corresponding experiment was conducted, and the results agreed well with the theoretical analysis. This method measures the detuning angles of the frequency converter in only one measurement and within 1min. The detuning angle measurement errors of KDP and KD*P crystals are less than 10µrad and 36.5-61.9µrad, respectively.

Broadband Up‐Conversion Mid‐Infrared Time‐Stretch Spectroscopy

AbstractTime‐stretch spectroscopy is a powerful tool for studying transient and nonrepetitive physical events. Its extension to the fundamental molecular fingerprint region is promising for chemical and biological research but encounters difficulties in mid‐infrared photodetection and strong attenuation of aqueous environments. Here, mid‐infrared time‐stretch spectroscopy via coincidently‐pumped nonlinear frequency conversion for efficient mid‐infrared generation and detection is demonstrated. Broadband (≈200 cm−1) mid‐infrared spectra at 77.5 Mspectra s−1 with high signal‐to‐noise ratio are recorded. The single‐shot signal‐to‐noise ratio (SNR) measured within 2 ns exceeds 200. The method reveals fast spectral dynamics in a laser‐induced liquid evaporation process with a temporal resolution of 12.9 ns. Furthermore, probing transient spectra during evaporation opens up a new opportunity for interrogating chemicals inside or behind a thick water layer. Integrating high speed, broad bandwidth, high SNR, and the potential for operating under an aqueous environment, this method will benefit many applications including molecular dynamics, chemical reactions, and biological diagnostics.

Detection of a Rotating Conveyor Roller Casing Vibrations on a Laboratory Machine

The article describes the basic parts and the overall design of the laboratory machine, which can be used to measure vibrations generated by a rotating conveyor roller attached to the flattened parts of its axis in the cut-outs of the conveyor idler support. On the structurally modified support of the conveyor idler consisting of the insertion of a plastic element placed between the roller axis and the support cut-out, the vibration acceleration values of the rotating roller from symmetric analysis were measured and compared with the values from asymmetric analysis of the traditional roller axis placement in the steel support. The size of the peripheral speed of the roller was determined, during the experimental measurements, by controlling the speed of the electric motor using a frequency converter. The obtained results of the measured values of vibration velocities in three mutually perpendicular planes showed a reduction in vibration values of about 15% when using plastic holders. The paper aims to present one of the possible technical solutions that can limit the vibration values transmitted to the supporting structure of the conveyor belt, generated by the rotating casing of the conveyor roller.

2637.5 nm Mid-infrared SrWO4 Raman laser intracavity-pumped by an actively Q-switched Ho:YAG laser

We first report a 2.6 µm mid-infrared SrWO4 Raman laser, intracavity-pumped by an actively Q-switched Ho:YAG laser. The 2122 nm fundamental laser was generated from the Ho:YAG laser, which was resonantly pumped by a 1908 nm continuous wave Tm:YLF laser. Based on the stimulated Raman scattering effect of SrWO4 crystal, the fundamental wavelength of 2122 nm was converted into the Raman wavelength of 2637.5 nm, corresponding to the Raman shift of 921 cm−1. The output characteristics of SrWO4 Raman laser were investigated at various repetition frequencies. The maximum average output power was 720 mW at the 6.6 W absorbed pump power and 4 kHz repetition frequency. The maximum single pulse energy and peak power were 196 μJ and 10.9 kW at the 5.6 W absorbed pump power and 3 kHz repetition frequency, respectively. The pulse Raman laser near 2.6 µm has potential applications in material processing, spectroscopy, remote sensing, and nonlinear frequency conversion.

The frequency control system of the screw unit with a solid rotor

This paper examines the features of construction and hardware implementation of the work control system of the screw-type multifunctional energy converter (MFEC). MFEC is an atypical electric machine, which is an induction motor with an external hollow solid rotor. Due to the presence of a ferromagnetic rotor, when power is supplied to the stator winding, the rotor is heated due to eddy currents and simultaneously rotates. In this way, it is possible to combine several functions at the level of the principle of operation in one device. However, such an electric machine as MFEC requires a special approach to management and ensuring the stability of operation. Thus, the task is complicated by the mechanical connection of several MFEC rotors into a single structure. The task of the control system includes not only ensuring a low speed of rotation of the general rotor of the MFEC, but also ensuring the value of the torque at the nominal level without losing the intensity of heating the rotor. Prerequisites for the practical solution of the given problems are preliminary theoretical studies of the authors and simulation modeling. The practical implementation of theoretical developments is considered in detail in this work. In particular, one MFEC module is supposed to be powered by a frequency converter in the mode of maintaining the specified rotation speed. The power supply of the second MFEC module is provided by an unregulated three-phase power source, which creates a torque opposite to that of the first MFEC module. The characteristics of this mode of operation, its purpose and influence on the initial characteristics of the screw unit are explained in detail in the relevant sections of this paper.

Electrically and all-optically switchable nonlocal nonlinear metasurfaces.

Nonlocal effects on metasurfaces play an important role to achieve high-Q spectral selectivity, beneficial for development of multifunctional, multispectral integrated optics. In addition, they enhance the optical interaction and promote a variety of nonlinear effects, including frequency conversion and stimulated scattering. Active tuning of nonlocal nonlinearity is highly desirable for sensing and signal processing but was hardly explored until now. Here, we show drastic electric and all-optical tunability of nonlocal second-harmonic generation (SHG) from nonlinear metasurface, functionalized with a twisted nematic liquid-crystal (LC) layer. The addition of LC results in the emergence of strong nonlocal SHG, due to a surface lattice resonance of the system. We demonstrate a notable enhancement of SHG on resonance, more than 25 dB electrical switching amplitude, and all-optically induced phase transition imprinted on SHG. Our results on dynamic nonlocal effects introduce a very promising route for active nonlinear optical metadevices at the nanoscale.

Instantaneous Square Current Signal Analysis for Motors Using Vision Transformer for the Fault Diagnosis of Rolling Bearings

Using vibration signals for bearing fault diagnosis can generally achieve good diagnostic results. However, it is not suitable for practical industrial applications due to the restricted installation and high cost of vibration sensors. Therefore, the easily obtainable motor current signal (MCS) has received widespread attention in recent years. Meanwhile, traditional fault diagnosis methods cannot meet the diagnostic accuracy requirements because of the low signal-to-noise ratio (SNR) of the MCS. Committed to achieving bearing fault diagnosis through MCS, a rolling bearing fault diagnosis method, ISCV-ViT, based on the MCS and the Vision Transformer (ViT) model, is proposed. In particular, a signal processing method based on the instantaneous square current value (ISCV) is proposed to process the MCS directly obtained through a frequency converter into time-domain images. Then, the ViT model is applied for bearing fault diagnosis. Finally, experimental verification is carried out based on the public bearing dataset of Paderborn University (PU) and the bearing dataset of Shenzhen Technology University (SZTU). The analysis of the experimental results demonstrates that the average accuracy of the ISCV-ViT for the two datasets is up to 96.60% and 94.87%, respectively.

Quantum frequency conversion using 4-port fiber-pigtailed PPLN module.

Quantum frequency conversion (QFC), which involves the exchange of frequency modes of photons, is a prerequisite for quantum interconnects among various quantum systems, primarily those based on telecom photonic network infrastructures. Compact and fiber-closed QFC modules are in high demand for such applications. In this paper, we report such a QFC module based on a fiber-coupled 4-port frequency converter with a periodically poled lithium niobate (PPLN) waveguide. The demonstrated QFC shifted the wavelength of a single photon from 780 to 1541 nm. The single photon was prepared via spontaneous parametric down-conversion (SPDC) with heralding photon detection, for which the cross-correlation function was 40.45 ± 0.09. The observed cross-correlation function of the photon pairs had a nonclassical value of 13.7 ± 0.4 after QFC at the maximum device efficiency of 0.73, which preserved the quantum statistical property. Such an efficient QFC module is useful for interfacing atomic systems and fiber-optic communication.

Inverter Heat Pumps as a Variable Load for Off-Grid Solar-Powered Systems

The capacity of electric air conditioning and heating systems is growing rapidly, as is the nameplate capacity of PV power plants. While the demand for cooling has a positive correlation with solar irradiance, the demand for heating has an opposite relation. In this study, different approaches to design (aggregation; thermal, battery, and implicit storage) and control (frequency conversion; variable and adaptive load) and their effects on the efficiency of an off-grid active thermal stabilisation system based on a solar-powered heat pump are analysed. The case considered is a permafrost thermal stabilisation system in Norway. It is shown that proper layout and control of the system with an adaptive load can reduce capital expenditures and the total cost of ownership by 30–40%. Increases in the capacity factor and cooling stability of the systems with aggregated and variable loads are studied. The downside is that there is an increase in the compressor’s operation time by 50% with a variable load and by 25% per unit with aggregation, which means more frequent replacement in terms of motor hours. The approaches considered are applicable in a wide range of solar-powered facilities with a positive correlation between solar irradiation and energy demand, but the results are quite case-sensitive. The prospects of using excess refrigerant and soil for thermal energy storage instead of traditional electrochemical batteries are considered.

Photonic generation of triangular waveform with tunable symmetry based on channelized frequency synthesis.

A symmetry tunable triangular waveform photonic generator based on channelized frequency synthesis is proposed and studied. The generator adopts a multichannel system architecture and harmonic amplitude control algorithm to physically isolate each subchannel. In a single subchannel, quadrature phase shift keying modulation and coherent dual-wavelength balanced detection are used to realize optical upconversion and suppress mixing interference in the process of frequency conversion. Therefore, the model has the characteristics of a high-order Fourier series fitting tunable function waveform output. The analysis results show that the Fourier series harmonic coefficients can be adjusted flexibly by the multivariable joint regulation algorithm. The relationship between the variables is analyzed and discussed. The feasibility of the scheme is verified by optical simulation; when the rms error (RMSE)≤0.03, a 20%-80% tunable symmetry triangular waveform can be obtained.

A Turn-Ratio-Changing Half-Bridge CLLC DC–DC Bidirectional Battery Charger Using a GaN HEMT

This paper presents a 250 kHz bidirectional battery charger circuit using a GaN HEMT. The charger is subjected to a high-/low-side constant voltage at 200 V/20 V. The charger circuit is a hybrid of the LLC and flyback circuit topologies. Both the power output analysis and efficiency control of this circuit are simplified when the magnetization current is minimized using the low-resistance GaN HEMT. The switching frequency is controlled to match the series resonance in a way that is analogous to conventional LLC circuit controls, while the duty ratio that determines the power output and the dead time, which determines the zero voltage switching, is controlled in an analogous manner to the flyback circuit control. The charging and discharging modes were altered by applying a double-throw relay that changes the transformer turn ratio, which is different from conventional LLC designs using the switching frequency adjustment. A nominal turn ratio with Np = 35 and Ns = 3.5 for a 200 V/20 V converter can only produce an internal series resonance with no current flowing in any charging direction. The proposed circuit using a transformer with multiple windings (Np = 35, Ns,F = 4, and Ns,R = 3) was fabricated to deliver 125 W output power from the power grid battery to the vehicle battery in the forward (charging) mode and 90 W in the reverse (discharging) mode. The conversion efficiency was calculated to be as high as 97% in the forward mode and 95% in the reverse mode. The high conversion efficiency is due to the characteristics of the GaN HEMT, including low resistive and switching losses. The equations derived in this paper associate these losses with the series resonant frequency and power conversion rate, which highlight the advantages of using a GaN HEMT in this CLLC design.

Microwave photonic dispersion immune self-interference cancellation scheme for a radio over fiber based in-band full duplex communication link

A microwave photonic scheme for multi-functional radio over fiber based in-band full duplex communication links to realize deep self-interference cancellation, long range transmission, and efficient signal recovery is proposed. In the proposed scheme, double sideband modulation helps avoid applying electrical couplers or optical filters and is beneficial to improve the frequency conversion efficiency. By virtue of the intermediate frequency signal amplitude regulation mechanism induced by fiber dispersion, the conditions of dispersion induced power fading compensation, amplitude matching, and phase reversion between self-interference and reference signals can be satisfied through joint DC bias tuning. The high precision delay matching in the optical domain is advantageous to the deep self-interference cancellation performance in a wide frequency range compared to its electrical counterparts. Furthermore, the deterioration of signal quality and self-interference cancellation performance caused by fiber dispersion is avoided. Experimental analyses show that a single tone signal in a wide frequency range of 2–20 GHz can be cancelled over 60 dB. A broadband signal with bandwidth of 50 MHz in the C-band, X-band, and K-band can be cancelled over 35 dB. Furthermore, the recovery performance of the signal of interest with different modulation formats and different signal to interference ratios is investigated, showing high quality signal transmission and efficient signal recovery. The capability of dispersion induced power fading compensation is also verified, and the spurious-free dynamic range is measured to be 88.47dB⋅Hz2/3.

Plasmonic Metasurfaces with Quality Factors Up to 790 in the Visible Regime

AbstractPlasmon metasurfaces supporting surface lattice resonances (SLRs) have emerged as an exciting platform for manipulating nanoscale light‐matter interactions in expanding applications. Although great progress has been achieved, the quality factors of plasmonic metasurfaces remain quite limited especially in the visible regime, hindering practical applications. This study reports an SLR‐based plasmonic metasurface with an ultrahigh quality factor that reaches 1427 in theory and 790 in experiments at 712 nm, a 240% increase over the state of the art. The quality factor of the out‐of‐plane SLR in periodic gold or silver nanorods is augmented by an order of magnitude through reducing the nanorod height from 100 to 50 nm. With these findings, this work is expected to pave the way for realizing high‐performance nanolasers, nonlinear frequency converters, and biosensors based on ultrahigh‐Q plasmonic metasurfaces.

CMOS spectrophotometric microsystem for malaria detection.

Optical spectrophotometry has been explored to quantify Plasmodium falciparum malaria parasites at low parasitemia, with potential to overcome the limitations of detection in the current diagnostic methods. This work presents the design, simulation and fabrication of a CMOS microelectronic detection system to automatically quantify the presence of malaria parasites in a blood sample. The designed system is composed by an array of 16 n+/p-substrate silicon junction photodiodes as photodetectors and 16 current to frequency (IF) converters. An optical setup was used to individually and jointly characterize the entire system. The IF converter was simulated and characterized in Cadence Tools using UMC 1180 MM/RF technology rules, featuring a resolution of 0.01 nA, a linearity up to 1800 nA and a sensitivity of 4430 Hz/nA. After fabrication in a silicon foundry, the photodiodes' characterization presented a responsivity peak of 120 mA/W (λ = 570 nm) and a dark current of 7.15 pA at 0 V. Regarding the IF converter, it exhibited high linearity (R2 ≈ 0.999) up to 30 nA, with a sensitivity of 4840 Hz/nA. Furthermore, the microsystem performance was validated using RBCs (Red Blood Cells) infected with P. falciparum and diluted at different parasitemia (12, 25 and 50 parasites/μL). The microsystem was able to distinguish between healthy and infected RBCs, with a sensitivity of 4.5 Hz/parasites.μL-1. The developed microsystem presents a competitive result, when compared to the gold standard diagnosis methods, with increased potential for malaria in field diagnosis.

A Temperature Compensated Voltage Controlled Relaxation Oscillator for Frequency Modulated DC-DC Charge Pump Regulation

Relaxation oscillators with wide dynamic range are required for low power frequency modulated switch mode DCDC regulator designs. In this brief, a temperature compensation technique with variable threshold control for Voltage Controlled Relaxation Oscillator (VCRO) is presented. The voltage to current conversion circuit reduces the drift in the frequency gain across temperature by introducing a PMOS-NMOS current gain compensation scheme. The current gain circuit also allows absolute control on the minimum value of control voltage after which VCRO starts doing voltage to frequency conversion. This restricts the amplifier to go out of saturation which is inherently generating the control voltage for VCRO. Measurement results show that across temperature range of -40 oC to 150 oC, the oscillator achieves a temperature stability of 187 ppm/oC at 18MHz and 171 ppm/oC at 92.5MHz respectively. Implemented in 90nm process node, it occupies 57μm×32μm area while dissipating 2.61 nW/KHz from a 1.5V supply.

Research on harmonic resonant fault mechanism and suppression measures of oilfield power grid based on fast mode analysis method

In recent years, with the use of electric drilling rig, electric fracturing pump, and other equipment, the harmonic resonance problem of oilfield power grid is becoming more and more serious. In view of the high time and space complexity and long calculation time of the traditional harmonic resonance analysis method, the improved power iteration method is combined with the traditional modal analysis method, and the harmonic resonance problem of the oilfield power grid is analyzed by the fast modal analysis method. At the same time, a new set of harmonic resonance amplification index is derived and verified, and the harmonic content amplification times in the resonant influence region and different busbars are revealed. And then a passive filter is used to suppress harmonic resonance, and the effectiveness of the scheme is verified by field tests. The results show that, in the frequency range of 0–1000 Hz, the resonant frequency points in the oil field are mainly related to the rectifier pulse number of the drilling rig and the frequency conversion device for fracturing. The proposed fast modal analysis method has the advantages of fast convergence speed and memory saving, which is helpful to accurately detect the harmonic resonance region caused by the multi-pulse frequency conversion device, and the harmonic resonance can be effectively suppressed by installing a filter at the main excitation bus of the resonant frequency.

Merging Effective Medium Concepts of Spatial and Temporal Media: Opening new avenues for manipulating wave-matter interaction in 4D

While wave-matter interactions can be tailored in space via spatial inhomogeneities in material parameters, temporal and spacetime media are becoming increasingly popular as they may enable the full control of electromagnetic (EM) waves in four dimensions (4D). Here, expanding our previous work on the effective medium concept of temporal media, we develop more general effective medium theories that combine spatial multilayered media with temporal multistepped changes of the permittivity. This work represents a combination of spatial and temporal inhomogeneities in a single structure. As the temporal modulation is applied within certain spatial multilayers (not all the layers), our approach may relax the need for temporally modulating the whole medium where the wave travels while still achieving frequency conversion (a key feature of temporal multistepped media). The theoretical formulation and closed-form expressions for the effective permittivity of such spacetime effective media are presented. The proposed structure is studied via numerical simulations, demonstrating the possibility of designing spacetime effective media using a combination of temporally and spatially modulated materials. The increased degrees of freedom provided by our approach may open new possibilities for manipulating wave-matter interaction in 4D.

Joint DOA-Distance Estimation Method for Radar Using a Novel Time-Domain Wideband Synthesis System

In this paper, a joint direction of arrival (DOA) and distance estimation (JDDE) method using a novel time-domain wideband synthesis signal system is proposed. In contrast to traditional time-domain synthesis methods, which transmit sub-pulses separately, a uniform linear array is used, and all stepped linear frequency modulated (SLFM) sub-pulses are transmitted simultaneously. The echo signal is mixed with each transmitted signal of the corresponding antenna and filtered to separate the single-frequency components from different targets and array elements for synthesis. Single-frequency components have different frequencies and discontinuous phases due to wave-way differences. To solve the problem that single-frequency components cannot be synthesized directly, the frequency and phase of single-frequency components need to be calibrated, including frequency conversion and phase shift, which require DOA information of the targets. Consequently, a high-precision DOA algorithm that employs phase difference fitting, along with the corresponding generic phase unwrapping algorithm, is designed for the characteristics of the arrays and signal system in this paper. After obtaining the DOA information, the wideband synthesis algorithm is applied to synthesize the single-frequency components to obtain high-resolution ranging results. The theoretical analysis and simulation results show that the method has high distance resolution and JDDE accuracy. In a multi-target environment, the number of targets is not limited by the number of antennas. In addition, unlike traditional wideband synthesis methods, the method utilizes multiple transmitting antennas to send SLFM signal pulses simultaneously rather than sequentially, which enhances the response speed of the radar.

PFDIR – A Wideband Photonic-Assisted SAR System

The next generation of synthetic aperture radar (SAR) systems will need transmit and receive analog signals over a wide frequency range with large bandwidth to fulfil the increasing demands. Since the performance of the digital microwave component is deteriorated at increasing frequency, radio frequency (RF) front-end with the capability of frequency conversion is needed for frequency beyond a few gigahertz. However, for the widely employed RF mixers, the inherent imperfect of I-V characteristics of nonlinear devices, generates many undesired mixing spurs which restricts on the instantaneous bandwidth and the spurious-free dynamic range (SFDR). At Aerospace Information Research Institute Chinese Academy of Sciences, a photonic-assisted front-end with functions of signal generation and deramp processing has been conceived and implemented in an experimental deramp-on-receive CW SAR system. The system is called PFDIR (Photonic-Assisted Front-End Deramp-on-Receive Imaging Radar) and is envisaged to obtain SAR imaging at high resolution. In current stage, the Ku-band system with a bandwidth of 5.72 GHz, corresponding to a relative bandwidth of 37.8%, operates well with a fixed two-horn antenna. The configuration of the photonic front-end and the system design are described. Ground-based tests and airborne imaging results with geometrical resolution down to 5 cm are presented.

Extraordinary Five-Wave Mixing in a Zinc Oxide Microwire on a Au Film.

Coherent multiwave mixing is in demand for optical frequency conversion, imaging, quantum information science, etc., but has rarely been demonstrated in solid-state systems. Here, we observed three- and five-wave mixing (5WM) in a c-axis growth zinc oxide microwire on a Au film with picosecond pulses in the near-infrared region. An output 5WM of 4.7 × 10-7 μW, only 2-3 orders smaller than the three-wave mixing, is achieved when the excitation power is as low as 1.5 mW and the peak power density as weak as ∼107 W/cm2. The excitation power dependence of 5WM agrees well with the perturbation limit under the low intensity but exhibits a strong deviation at a high pumping power. This extraordinary behavior is attributed to the cooperative resonant enhancement effect when pumping in the near-infrared range. Our study offers a potential solid-state platform for on-chip multiwave mixing and quantum nonlinear optics, such as generating many-photon entangled states or the construction of photon-photon quantum logic gates.