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- 2019
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- anharmonic Bloch oscillations
- coupled mode method
- array of waveguides
- active harmonic filter
- Multifunctional VSC
- unity power factor operation
- power quality improvement
- grid-connected SPV system
- renewable energy sources
- Optoelectronic Information Science and Engineering
- Electrical Engineering and Automation
- Shevchenko Pridnestrovskii State University
- Malaviya National Institute of Technology
- Academy of Sciences of Moldova
- IIITD&M Kancheepuram
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In2Se3 nanosheets for harmonic mode-locked fiber laser
摘要： Two-dimensional materials with a sheet structure have excellent optical, electrical and mechanical properties, and have attracted much attention in recent years, especially In2Se3 (the N-type semiconductor compound), which has a rapid development in the fields of materials science and optical communication. In this paper, the nonlinear saturation absorption characteristics of In2Se3 are studied. The In2Se3 nanosheet dispersion can be used in ultrafast photonics applications. The nonlinear absorption is measured by power correlation method, and the modulation depth and saturation intensity are 3.8 % and 246.6 MW/cm2, respectively. More importantly, In2Se3 is used as a saturable absorber (SA) in a passively mode-locked erbium-doped fiber laser. The proposed mode-locked fiber laser is demenstrated with a center wavelength of 1529.4 nm, a fundamental frequency of 5.9 MHz, a spectral width of 3.96 nm, a pulse width of 1.38 ps, and a signal-to-noise ratio of 55 dB. For the first time, harmonic mode-locking with a high-repetition rate of 431 MHz is achieved when the pump power is 360 mW corresponding to 73rd-order harmonic mode locking. It can be seen that In2Se3 is indeed a new excellent photonic material, which can be used in fiber optic communication, SAs photonics,, laser material processing and light modulators.
关键词： harmonic mode-locked,high repetition frequency,mode-locked,In2Se3 SA
更新于2025-09-23 15:21:01
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Improved-efficiency quasi-two-stage current-source-mode SIMO LED driver
摘要： The paper presents a modularized control strategy of doubly fed induction generator (DFIG) system, including the grid-side converter (GSC) and rotor-side converter (RSC), under unbalanced and harmonic grid voltage. The sequence decomposition process and complicated control reference calculation can be avoided in the proposed control strategy. From the perspective of power grid friendly operation, the control targets of DFIG system in this paper are chosen as: 1) smooth active and reactive power injected into the power grid; 2) balanced and sinusoidal current injected into the power grid. The RSC and GSC can work as two independent modules and the communication between RSC and GSC can be removed. Furthermore, the third harmonic current component, dc-link voltage fluctuation, and electromagnetic torque pulsation under the different control targets are theoretically analyzed. Finally, the availability of the proposed modularized control strategy of DFIG system under unbalanced and distorted grid voltage is verified by experiment results.
关键词： unbalanced and harmonic grid voltage,modularized control,doubly fed induction generator (DFIG) system,smooth active and reactive power,Balanced and sinusoidal current
更新于2025-09-23 15:21:01
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Cooper minimum of high-order harmonic spectra from an MgO crystal in an ultrashort laser pulse
摘要： Cooper minimum structure of high-order harmonic spectra from atoms or molecules has been extensively studied. In this paper, we demonstrate that the crystal harmonic spectra from an ultrashort midinfrared laser pulse also exhibit the Cooper minimum characteristic. Based on the accurate band dispersion and k-dependent transition dipole moment (TDM) from the ?rst-principles calculations, it can be found that the harmonic spectra from the MgO crystal along the (cid:2)-X direction present a dip structure in the plateau, which is originated from the valley of TDM by examining the distribution of the harmonic intensity at the k space. The Cooper minimum feature in crystal high-order-harmonic generation (HHG) will pave a new way to retrieve the band information of solid materials by using HHG from the ultrashort midinfrared laser pulse.
关键词： transition dipole moment,ultrashort laser pulse,Cooper minimum,MgO crystal,high-order harmonic generation
更新于2025-09-23 15:21:01
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Harmonic Characterizations of Loaded Resonators for Waveguide Filters
摘要： A new method of controlling and predicting the harmonic responses, for spurious-free window improvement of millimeter-wave bandpass filters, with complete mathematical derivation, is presented in this paper. This method relies on loading a transmission line resonator with inverters, permitting the increase/ decrease of the harmonics-to-fundamental ratios, for predetermined inverter coupling values. It is a universal method based on circuit models and mathematical theories, independent of the fabrication implementation; only typical bandpass filter inverters are necessary. It does not affect or include the design of input/ output resonator ports, with materials and dimensions, introducing the least design complexity, cf. other earlier approaches. Resonators and bandpass filters using substrate integrated waveguide technology are designed, simulated, fabricated, measured and validated. The derived models, simulations and measured results are in good agreement. The control of the harmonic performance is demonstrated by comparing the measurements of two bandpass filters fabricated with-waveguides, in the millimeter-wave band 27.9 to 29.5 GHz. The inverter-loaded resonators, is analyzed versus a conventional iris filter operating with the TE10 mode. The comparisons of the simulations and measurements of the two filters demonstrate experimentally the possibility of the systematic control of the harmonics-to-fundamental ratios of the proposed theoretical analysis.
关键词： harmonic suppression,substrate integrated waveguide,Filters,higher-order modes,millimeter-wave,waveguide
更新于2025-09-23 15:21:01
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Sierpi??ski Fractals as Plasmonic Metastructures for Second-Harmonic Generation
摘要： Metallic Sierpiński fractal metastructures made of gold nanoprisms that exhibit compatibility for both surface-enhanced Raman spectroscopy and second-harmonic generation have been prepared by electron-beam lithography. A sequential series of Sierpiński patterns were investigated up to the eighth-order generation. The presence of localized surface plasmon modes in the visible spectral range is due to the arrangement of the individual triangles forming the Sierpiński geometry, and was first exploited for surface-enhanced Raman measurements after functionalization of the plasmonic platform with p-Nitrothiophenol. Due to the non-centrosymmetric arrangement of the individual nanoprisms within the Sierpiński pattern, second-harmonic generation (SHG) microscopy measurements were conducted to evaluate the second-order nonlinear optical activity and its relationship to the spatial distributions of electromagnetic enhancement over the surface of the metastructure. Functionalization of the surface with molecules with an electron withdrawing group appears to further enhance the surface SHG signal.
关键词： Metamaterials,Plasmonics,Fractal plasmonics,Surface-enhanced Raman,Second-harmonic generation
更新于2025-09-23 15:21:01
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Influence of intensity ratio of the two driving laser fields on the cutoff of the high-order harmonics
摘要： We investigate the high-order harmonic generation (HHG) of the helium atom at the various intensity ratios of the counter-rotating two-color circularly polarized laser fields. The results show that the cutoff energy of the harmonic spectra can be affected by changing the intensity ratios. By comparing the results from different intensity ratios, we find that the distances the electrons travel are short when the intensity ratio is increased. The dependence of the cutoff position in the HHG on the intensity ratios usually results from the classical trajectories of the electrons. As the intensity ratio increases, the electrons cannot be accelerated and it will gain less energy. As a result, the harmonic spectra are cut off at the lower energy. We compare the quantum and classical trajectories results to illustrate the reasons of the cut off dependence.
关键词： intensity ratios,cutoff energy,high-order harmonic generation,two-colour circularly polarized laser fields
更新于2025-09-23 15:21:01
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Homogenization of time-harmonic Maxwella??s equations in nonhomogeneous plasmonic structures
摘要： We carry out the homogenization of time-harmonic Maxwell’s equations in a periodic, layered structure made of two-dimensional (2D) metallic sheets immersed in a heterogeneous and in principle anisotropic dielectric medium. In this setting, the tangential magnetic field exhibits a jump across each sheet. Our goal is the rigorous derivation of the effective dielectric permittivity of the system from the solution of a local cell problem via suitable averages. Each sheet has a fine-scale, inhomogeneous and possibly anisotropic surface conductivity that scales linearly with the microstructure scale, d. Starting with the weak formulation of the requisite boundary value problem, we prove the convergence of its solution to a homogenization limit as d approaches zero. The effective permittivity and cell problem express a bulk average from the host dielectric and a surface average germane to the 2D material (metallic layer). We discuss implications of this analysis in the modeling of plasmonic crystals.
关键词： Jump condition on hypersurface,Time-harmonic Maxwell’s equations,Layered structures,Two-scale convergence,Homogenization
更新于2025-09-23 15:21:01
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Semi-integer harmonic generation from an argon atom by bichromatic counter-rotating circularly polarized laser field
摘要： We theoretically investigated the properties of the high-order harmonic generation from an argon atom by bichromatic counter-rotating circularly polarized (BCCP) laser field. The harmonic spectra are gradually splitting and the harmonic orders move towards the higher frequency. Meanwhile, the integer and semi-integer harmonic emission will be generated when the frequency ratios of right- and left-circularly polarized laser are semi-integer. The emission mechanism of the semi-integer-order harmonics have been investigated by using the rules of photon absorption and emission.
关键词： bichromatic counter-rotating circularly polarized laser field,photon absorption and emission,high-order harmonic generation,semi-integer-order
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE 3rd Conference on Energy Internet and Energy System Integration (EI2) - Changsha, China (2019.11.8-2019.11.10)] 2019 IEEE 3rd Conference on Energy Internet and Energy System Integration (EI2) - Harmonic Current Detection and Reactive Power Compensation Method for Photovoltaic System Based on FBD Method
摘要： In order to improve the equipment utilization of distributed photovoltaic power generation system, the harmonic and reactive currents generated by grid-connected photovoltaic can be accurately detected and compensated. A phase-locked loop based on second-order generalized integrator (SOGI-PLL) is introduced into the traditional FBD current detection method to separate the positive and negative sequence components of unbalanced voltage and detect the phase and frequency of reference voltage more accurately. The simulation results show that the algorithm can reduce the computational complexity and increase the detection accuracy and steady-state performance.
关键词： harmonic current detection,reactive power compensation,improved FBD method,grid-connected PV system,SOGI-PLL
更新于2025-09-23 15:21:01
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Ultrafast response of harmonic modelocked THz lasers
摘要： The use of fundamental modelocking to generate short terahertz (THz) pulses and THz frequency combs from semiconductor lasers has become a routine affair, using quantum cascade lasers (QCLs) as a gain medium. However, unlike classic laser diodes, no demonstrations of harmonic modelocking, active or passive, have been shown in THz QCLs, where multiple pulses per round trip are generated when the laser is modulated at the harmonics of the cavity’s fundamental round-trip frequency. Here, using time-resolved THz techniques, we show for the ?rst time harmonic injection and mode-locking in which THz QCLs are modulated at the harmonics of the round-trip frequency. We demonstrate the generation of the harmonic electrical beatnote within a QCL, its injection locking to an active modulation and its direct translation to harmonic pulse generation using the unique ultrafast nature of our approach. Finally, we show indications of self-starting harmonic emission, i.e., without external modulation, where the QCL operates exclusively on a harmonic (up to its 15th harmonic) of the round-trip frequency. This behaviour is supported by time-resolved simulations of induced gain and loss in the system and shows the importance of the electronic, as well as photonic, nature of QCLs. These results open up the prospect of passive harmonic modelocking and THz pulse generation, as well as the generation of low-noise microwave generation in the hundreds of GHz region.
关键词： harmonic modelocking,ultrafast response,THz QCLs,terahertz pulses,quantum cascade lasers
更新于2025-09-23 15:21:01