Asymmetric Modulation Research Articles

Modulation for Redox States of Single-Walled Carbon Nanotubes: Effect of Wrapping Conjugated Polymers.

Controlling the redox states of single-walled carbon nanotubes (SWNTs) is important for the optimization of their real performances in various fields. By means of in situ photoluminescence (PL) spectroelectrochemical measurements, we report a successful modulation for the redox parameters (redox potentials and electrochemical band gap) of (6,5) and (7,5)SWNTs with a simple change in conjugated polymers (CPs) non-covalently wrapped on the nanotubes. The large shift in the band gap (187 meV for (6,5)SWNTs and 101 meV for (7,5)SWNTs) was connected to the prominent difference in the interactions between the CPs and SWNTs as suggested by molecular dynamics (MD) simulations, while a striking difference in the 𝜋-electrons states of CP/SWNTs enabled the tuning of SWNTs' electronic states. Asymmetrical modulation for the reduction potential (LUMO) and oxidation potential (HOMO) of the SWNTs was observed as well. Our results can be promising for a simple but precise control of the electric states of SWNTs.

Asymmetric coordinative modulation boosting the activity and thermal stability of Pt1/CeO2 for CO oxidation under harsh condition

Supported metal catalysts play a central role in chemical industry, but it remains a formidable challenge to realize high activity while maintaining atomically dispersed status to maximize atom efficiency under harsh conditions. Herein, a novel strategy of constructing asymmetric coordination Pt active sites via coating N-doped carbon onto ceria supported Pt single atoms (Pt1/CeO2@CN) is proposed, through which superior low-temperature CO oxidation activity and satisfactory thermal stability are achieved simultaneously. Experimental and density functional theory results confirm that the unique asymmetric N2-Pt1-O2 coordinative configuration on Pt1/CeO2@CN tailors the electronic properties of Pt 5d states, increasing the turnover frequency by 15 times for CO oxidation at 120 °C compared with that on Pt1/CeO2 and sustaining the atomically dispersed status of Pt at as high as 400 °C under H2-containing atmosphere. This strategy suggests a promising avenue to fabricating highly active and stable supported metal catalysts for practical applications under harsh conditions.

Dual-polarization carrier-assisted differential detection with asymmetric twin-SSB modulation and simplified receiver structure

Carrier-assisted differential detection (CADD) is a promising solution for high-capacity and cost-sensitive short-reach application scenarios, in which the optical field of a complex-valued double-sideband (CV-DSB) signal is reconstructed without using a local oscillator laser. In this work, we propose a polarization division multiplexed asymmetric twin single-sideband CADD (PDM-ATSSB CADD) scheme to realize the optical field recovery of the PDM CV-DSB signals. The polarization fading is solved by using a pair of optical bandpass filters (OBPFs) to suppress the unwanted other polarized offset carrier and signal, and the dual-polarization optical field is recovered by the CADD receiver. An asymmetric twin-SSB signal is used to relax the sharpness requirement of optical filter edges. We also propose a joint signal-signal beat interference (SSBI) iterative mitigation algorithm, which can effectively mitigate intra- and inter-polarization SSBI. The proposed PDM-ATSSB CADD scheme is validated for 30 Gbaud PDM asymmetric twin-SSB 16-ary quadrature amplitude modulation signals. We illustrate the parameter optimization process for PDM-ATSSB CADD, including optical delay and the number of iterations. The impacts of phase noise and relative intensity noise for laser and polarization impairment on PDM-ATSSB CADD are evaluated through numerical simulation. Compared with the PDM-symmetric-TSSB CADD (PDM-STSSB CADD), the required frequency gap to reach the 7% FEC threshold can be reduced by 1 GHz, and the OSNR sensitivity is improved by about 3 dB. Moreover, two simplified PDM-ATSSB CADD schemes are proposed and discussed, which could be considered hardware-efficient and integrative candidates for metro and inter-data center interconnects.

Noncirculating current series resonant converter with pulse frequency modulation

SummaryIn this paper, an asymmetric pulse frequency modulation (APFM) is applied to the full‐bridge series resonant converter with a secondary LC resonant tank. Different from the traditional PFM, the upper and lower switches have complementary gate drivers and the lower switches have constant on time of half‐resonant period in this paper. Thanks to the resonant tank moved to the secondary side with the adopted APFM, the maximum magnetic flux density Bm of a high‐frequency transformer (HFT) is only concerned with the fixed resonant frequency rather than the variable switching frequency. Hence, the switching frequency can be widely regulated, as well as the voltage gain. Furthermore, the circulating current flowing back to the input voltage source in the traditional LC series resonant converter can be eliminated by the APFM, leading to a low resonant current peak value. The operation principles and characteristics of the adopted method are analyzed in detail. Finally, a 500 W/70–120 V to 300 V/21–180 kHz prototype is built, and the experimental results verified the theoretical analysis well.

Asymmetric convolutional modulation network for efficient image super-resolution

Thanks to the effectiveness of large kernel convolutions in acquiring large receptive fields, lightweight single image super-resolution (SISR) approaches based on large kernel designs have achieved significant performance. However, these state-of-the-art methods still require high computational costs, and their model efficiency remains to be improved. To address these challenges, we propose an asymmetric convolutional modulation network (ACMN) for efficient image super-resolution. In detail, we design an asymmetric convolutional modulation unit (ACMU) that combines large kernel design and modulation mechanism for adaptively selecting representative features from a large receptive field. Furthermore, we adopt depth-wise asymmetric convolutions to further reduce computational burden. To supplement the local context information and promote inter-channel interaction, we further develop a channel shuffle feedforward network (CSFN) to extract local feature information and facilitate inter-channel information interaction. Experimental results demonstrate that our ACMN outperforms other state-of-the-art efficient SR methods with fewer parameters and Multi-Adds.

Meta-Signal Processing with Data/Pilot Combining for Beidou B2 Signals

Beidou Navigation Satellite System (BDS) third generation satellites currently broadcast Open Service (OS) signals into two closely spaced Radio Frequencies (RFs) in the B2 band. These are the B2a and B2b signal components, which form the current implementation of the Asymmetric Constant-Envelope Binary Offset Carrier (ACE-BOC) modulation. The B2a signal features both a data and a pilot channel, whereas the B2b component is data only with data symbols of 1 ms duration. The absence of a pilot channel and the fast data rate make the processing of the B2b component challenging. Tracking performance can, however, be improved by jointly processing the B2a and B2b components. In this respect, meta-signal approaches are investigated for jointly processing the B2a and B2b signals. Two meta-signal tracking architectures are proposed: the first considers the pilot channel of the B2a component and the data channel of the B2b signal. The second exploits all the power available and also implements data/pilot combining on the B2a channel. Both architectures allow the extension of the integration time beyond the data symbol duration using non-coherent approaches. Theoretical results are supported by simulations and real data analysis performed using a custom Software Defined Radio (SDR) receiver. Simulation and experimental results clearly show the benefits of the meta-signal approach, which can be effectively adopted for the processing of asymmetric modulations such as the current implementation of the ACE-BOC, which lacks a pilot channel on the B2b component.

Refractive index sensing characteristics of long-period gratings in linearly arranged three-core fiber

We demonstrate the refractive index (RI) sensing characteristics of long-period gratings (LPGs) in linearly arranged three-core fiber (TCF), which are fabricated using arc discharge technique. Due to the asymmetric index modulation during fabrication, the RI sensitivity of TCF-LPGs in the 0° grating inscription direction is greater than that in the 90° grating inscription direction. The spectral and RI sensing characteristics of TCF-LPGs in the 0° grating inscription direction with different grating periods have been investigated experimentally. In the RI range from 1.4538 to 1.4589, the resonance at 1533.3 nm for TCF-LPGs with grating period of 465 μm could achieve the RI sensitivity of 15943.3 nm/RIU, which could be optimized to 18160.7 nm/RIU at 1676.3 nm as the TCF-LPGs with grating period of 600 μm. Moreover, the proposed TCF-LPGs exhibit notably greater RI sensitivity compared to arc-discharged LPGs in conventional single-mode fibre, presenting substantial advantage in RI sensing. And, changing the polarization state of the incident light enhances the RI sensitivity of TCF-LPGs.Additionally, the influence of bending or temperature interference on the RI sensitivity of TCF-LPGs is minimal, ensuring that interference with RI measurements can be neglected. The proposed sensor boasts cost-effectiveness, simplicity in structure, and high sensitivity to RI, showing substantial potential for applications in chemical and biological sensing.

Self-compression of laser pulses induced by asymmetric self-phase modulation aided by backward Raman scattering in periodic density-modulated plasma.

Here a mechanism for self-compression of laser pulses is presented, based on period density-modulated plasma. In this setup, two pump beams intersect at a small angle within the plasma. This interaction is facilitated by the ponderomotive ion mechanism, which causes a modulation in the density of plasma with long wavelengths and low amplitude. This modulation enhances the backward Raman scattering of the probe pulse. The trailing edge of the probe experiences greater energy loss, resulting in a steeper intensity gradient. This, in turn, induces an asymmetric self-phase modulation, which elevates the instantaneous frequency. It is notable that the laser in plasma exhibits opposite group velocity dispersion compared to traditional solid-state media. This unique property allows laser pulses to undergo dispersion compensation while broadening the spectrum, ultimately leading to self-compression. The 2D-PIC simulations demonstrate these phenomena, highlighting how period density-modulated plasma contributes to an asymmetric spectral distribution. The intricate interplay among self-phase modulation, group velocity, and backward Raman scattering results in the self-compressing of the laser pulse. Specifically, the pulses are compressed from their Fourier transform limit duration of 50 fs to a significantly reduced duration of 8 fs at plasma densities below 1/4 critical density, without the transverse self-focusing effects.

Dual-Side Asymmetric Duty Modulation Based on Accurate Soft-Switching Characteristics Modeling for DAB-Based DC Microgrid

Dual-Side Asymmetric Duty Modulation Based on Accurate Soft-Switching Characteristics Modeling for DAB-Based DC Microgrid

Upgraded architecture of TWDM-PON with type B protection for capacity and budget improvement

The next-generation mobile fronthaul system based on technologies beyond 5G requires optical access networks with excellent disaster resistance. For passive optical networks (PONs), also known as economical optical access networks, the Type B protection method that considers disaster resistance is a practical conventional approach to address transceiver and link failure. However, the transmission capacity upgrade and effective utilization of optical power of time wavelength division multiplexing (TWDM)-based-PON with Type B protection have not been extensively studied. In this study, we intend to upgrade the architecture by applying Type B protection to a 40 Gbit/s-class TWDM-PON that uses the uplink C band/downlink L band specified by NG-PON2. To improve the downlink capacity, we have considered a bidirectional asymmetric modulation transmission system to introduce a dual-polarization quadrature phase-shift keying system for the downlink C band. The downlink coherent signal is transmitted by selecting either the primary or secondary link using the optical switch. There are no major drawbacks with either the primary or secondary link. Moreover, we have numerically and experimentally clarified the impact of improving the reception power by receiving a burst single-input multi-output in the uplink under the condition of no link failure. Additionally, we describe the bidirectional transmission feasibility of C-band asymmetric modulation under link failure and reflection. We have found that bidirectional transmission at the same wavelength is possible by allowing a specific penalty even for asymmetric symbol rate/polarization/modulation formats. A principle verification experiment revealed that SIMO reception could be improved by a 1.5 dB budget on the uplink. The method of upgrading the TWDM-PON system can be changed while effectively using NG-PON2 technology until the future coherent PON method is completely introduced.

Creating Anti-Chiral Exceptional Points in Non-Hermitian Metasurfaces for Efficient Terahertz Switching.

Non-Hermitian degeneracies, also known as exceptional points (EPs), have presented remarkable singular characteristics such as the degeneracy of eigenvalues and eigenstates and enable limitless opportunities for achieving fascinating phenomena in EP photonic systems. Here, the general theoretical framework and experimental verification of a non-Hermitian metasurface that holds a pair of anti-chiral EPs are proposed as a novel approach for efficient terahertz (THz) switching. First, based on the Pancharatnam-Berry (PB) phase and unitary transformation, it is discovered that the coupling variation of ±1 spin eigenstates will lead to asymmetric modulation in two orthogonal linear polarizations (LP). Through loss-induced merging of a pair of anti-chiral EPs, the decoupling of ±1 spin eigenstates are then successfully realized in a non-Hermitian metasurface. Final, the efficient THz modulation is experimentally demonstrated, which exhibits modulation depth exceeding 70% and Off-On-Off switching cycle less than 9ps in one LP while remains unaffected in another one. Compared with conventional THz modulation devices, the metadevice shows several figures of merits, such as a single frequency operation, high modulation depth, and ultrafast switching speed. The proposed theory and loss-induced non-Hermitian device are general and can be extended to numerous photonic systems varying from microwave, THz, infrared, to visible light.

Asymmetric two-dimensional diffraction grating via a vortex field in an inverted-Y-type atomic system

We propose a theoretical scheme to realize a two-dimensional (2D) diffraction grating in a four-level inverted-Y-type atomic system coupled by a standing-wave (SW) field and a Laguerre–Gaussian (LG) vortex field. Owing to asymmetric spatial modulation of the LG vortex field, the incident probe field can be lopsidedly diffracted into four domains and an asymmetric 2D electromagnetically induced grating is created. By adjusting the detunings of the probe field and the LG vortex field, the intensities of the LG vortex field and the coherent SW field, as well as the interaction length, the diffraction properties and efficiency, can be effectively manipulated. In addition, the effect of the azimuthal parameter on the Fraunhofer diffraction of the probe field is also discussed. This asymmetric 2D diffraction grating scheme may provide a versatile platform for designing quantum devices that require asymmetric light transmission.

Closed-Form Continuous Asymmetrical Hybrid Modulation, Ensuring Wide ZVS Range and Seamless Transients for DAB Converters

Closed-Form Continuous Asymmetrical Hybrid Modulation, Ensuring Wide ZVS Range and Seamless Transients for DAB Converters

Power quality improvement of PWM AC Chopper fed capacitor run induction motor using BFO, PSO and CSO Algorithm

This paper exhibits performance enhancement of PWM AC chopper fed capacitor run induction motor by using optimization algorithm. The PWM AC chopper utilizes enhanced asymmetrical pulse width modulation technique by incorporating four pulses in quarter cycle. The switching instants are obtained optimally by bacteria foraging optimization, particle swarm optimization and cuckoo search optimization algorithm. The power quality parameters considered in this paper are total harmonic distortion of current, total harmonic distortion of voltage, power factor and efficiency. The simulation result shows that proposed algorithm shows better performance compared to other optimization techniques.

Hybrid transmission of PS-GS4QAM and QPSK data in the form of a PS-16QAM mm-wave signal enabled by optical asymmetrical dual-SSB modulation

The independent optical dual-single-sideband (dual-SSB) signal generation and detection can be achieved by an optical in-phase/quadrature (I/Q) modulator and one single photodiode (PD). The dual-SSB signal is able to carry two different information. After PD detection, the optical dual-SSB signal can be converted into an electrical millimeter-wave (mm-wave) signal. Therefore, the optical dual-SSB signal generation and detection technique can be employed in the radio-over-fiber (RoF) system to achieve higher system spectral efficiency and reduce system architecture complexity. However, the I/Q modulator's nonideal property results in the amplitude imbalance of the optical dual-SSB signal, and then the crosstalk can occur. Moreover, after PD detection, the generated mm-wave signal based on the optical dual-SSB modulation has a relatively low signal-to-noise ratio (SNR), which restricts the system performance. In this paper, we propose an optical asymmetrical dual-SSB signal generation and detection scheme based on the probabilistic shaping (PS) technology, to decrease the influence of the optical dual-SSB signal’s amplitude imbalance and to enhance the system performance in the scenario of the limited SNR. The dual-SSB in our scheme is composed of the left sideband (LSB) in probabilistic-shaping geometric-shaping 4-ary quadrature amplitude modulation (PS-GS4QAM) format and the right sideband (RSB) in quadrature phase-shift keying (QPSK) format. The transmitter digital signal processing (DSP) generates a dual-SSB signal to drive the optical I/Q modulator. The I/Q modulator implements an electrical-to-optical conversion and generates an optical dual-SSB signal. After PD detection, the optical dual-SSB signal is converted into a PS-16QAM mm-wave signal. In our simulation, compared with the normal 16QAM scenario, the PS-16QAM scenario exhibits a ∼1.2 dB receiver sensitivity improvement at the hard-decision forward error correction (HD-FEC) threshold of 3.8×10−3. Therefore, in our experiment, based on the PS technology, we design a dual-SSB signal including a 5 Gbaud LSB-PS-GS4QAM at −15 GHz and a 5 Gbaud RSB-QPSK at 20 GHz. After 5 km standard single-mode fiber (SSMF) transmission and PD detection, the dual-SSB signal is converted into a 5 Gbaud PS-16QAM mm-wave signal at 35 GHz. Then, the generated PS-16QAM signal is sent into a 1.2 m single-input-single-output (SISO) wireless link. In the DSP at the receiver end, the dual-SSB signal can be recovered from the mm-wave signal, and the PS-GS4QAM and QPSK data carried by the dual-SSB signal can be separated. The bit error rates (BERs) of the LSB-PS-GS4QAM and the RSB-QPSK in our experiment can be below the HD-FEC threshold of 3.8×10−3. The results demonstrate that our scheme can tolerate the I/Q modulator’s nonideal property and performs well in the scenario of a relatively low SNR.

Switching of topological phase and topological channel via asymmetric hopping modulations in a one-dimensional superconducting circuit lattice

We propose a theoretical scheme for a one-dimensional superconducting circuit lattice system to achieve that topological phase transition and topological multi-channel transfer, which is adjusted by the asymmetric hopping modulations. The system consists of an array of coupled superconducting microwave cavities, the hopping between its can be modulated by the qubits. Here, we explore topological stages by introducing parameters to expand the hopping modulation range. We found that the energy bands in the system exhibit different structural characteristics, which can achieve topological phase switching. Meanwhile, the edge modes can undergo a flipping process, which can not only realize dual-channel topological quantum information transfer, but also can achieve four-channel. Furthermore, it is noted that the defect can induce new topological phases, which can be optimized by adjusting the hopping parameters, while disorder can only cause band fluctuations and inversions, but does not change the position and period of edge states, verifying that the edge state transport is robust. The results obtained in this work can be applied to the storage and transmission of quantum information, and have a guiding role in the future development of quantum technology.

Kinetic behavior of secondary electrons in a magnetized voltage-driven discharge using combined rf/dc sources

This study employed particle-in-cell/Monte Carlo simulations, along with test particle methods, to examine the characteristics of secondary electrons (SEs) in a voltage-driven discharge using combined rf/dc sources and operates in the presence of a magnetic field. The behavior of SEs is significantly influenced by the magnetic field, leading to the emergence of complex branches in temporal electron energy probability distributions and spatiotemporal electron density distributions within the sheath. The number of branches is directly correlated to the cyclotron period. Moreover, the application of a direct current (dc) source thickens the sheath at the dc biased electrode while attenuating the sheath on the opposite side. This leads to an asymmetrical modulation of the kinetic behavior of SEs in the two sheaths, ultimately resulting in a substantial increase in electron energy on the side of the dc biased electrode.

A Symmetric Sixth-Order Step-Up Converter with Asymmetric PWM Achieved with Small Energy Storage Components

This research explores an improved operation of a recently studied converter, the so-called two-phase sixth-order boost converter (2P6OBC). The converter consists of a symmetric design of power stations followed by an LC filter; its improved operation incorporates an asymmetric pulse width modulation (PWM) scheme for transistor switching, sometimes known as an interleaved PWM approach. The new operation leads to improved performance for the 2P6OBC. Along with studying the 2P6OBC, one of the contributions of this research is providing design equations for the converter and comparing it versus the interleaved (or multiphase) boost converter, known for its competitiveness and advantages; the single-phase boost topology was also included in the comparison. The comparison consisted of a design scenario where all converters must achieve the same power conversion with an established maximum switching ripple, and then the stored energy in passive components is compared. Although the 2P6OBC requires a greater number of components, the total amount of stored energy is smaller. It is known that the stored energy is related to the size of the passive components. Still, the article includes a discussion of this topic. The new operation of the converter offers more streamlined, cost-effective, and efficient alternatives for a range of applications within power electronics. The final design of the 2P6OBC required only 68% of the stored energy in inductors compared to the multiphase boost converter, and 60% of the stored energy in capacitors. This result is outstanding, considering that the multiphase boost converter is a very competitive topology. Experimental results are provided to validate the proposed concept.

Asymmetric optical properties and bandgap shift of pre-strained flexible ZnO films

Strain engineering has been extensively explored to modulate the various intrinsic properties of flexible inorganic semiconductor films. However, experimental characterization of tensile and compressive strain-induced modulation of optoelectronic properties and their differences has not been easily implemented in flexible inorganic semiconductor films. Herein, the strain-dependent structural, optical, and optoelectronic properties of flexible ZnO films under pre-tensile and pre-compressive strains are systemically investigated by a Mueller matrix ellipsometry-based quantitative characterization method combined with x-ray diffraction and first-principle calculation. With extended prestress-driven deposition processing under bi-direction bending modes, pre-tensile and pre-compressive strains with symmetric magnitudes can be achieved in flexible ZnO films, which allows precise observation of the strain-driven asymmetric modulation of optoelectronic properties. When the applied prestrain varies approximately equally from 0% (baseline) to −0.99% (compression) and 1.07% (tensility), respectively, the relative changes for the c-axis lattice constant are 0.0133 and 0.0104 Å, respectively. Meanwhile, the dependence factors of the bandgap energy on the pre-compression and pre-tensile strains were determined as −0.0099 and −0.0156 eV/%, respectively, and the complex refractive index also presents an asymmetric varying trend. With the help of the strain–stress analysis and the first-principle calculation, the intriguing asymmetric strain-optical modulation effect could be attributed to the biaxial strain mechanism and the difference in the deformation potential between the two prestrain modes. These systematic investigation consequences are thus promising as a basis for the booming applications of the flexible inorganic semiconductor ensemble.

A Full-Power-Range Optimization Scheme Under Double-Side Asymmetrical Phase-Shift Modulation in DAB-Based Distributed Energy Storage System

For distributed energy storage system, dual-active-bridge (DAB) is often employed as interface among photovoltaic port, storage system and load. Efficient DAB operation will be beneficial to energy conversion efficiency. Nevertheless, for conventional DAB modulation, many problems exist including that wider soft-switching range is always accompanied with high peak current. In order to overcome these problems, a double-side asymmetrical phase-shift modulation (DAPM) is proposed, which combines phase-shift modulation on the primary side and variable-duty modulation on the secondary side. Based on DAPM, a full-power-range optimization scheme is employed to reduce current stress and widen zero-voltage-switching (ZVS) range. Consequently, most of DAPM modes can realize all semiconductors ZVS. ZVS ranges are widened dramatically with lower peak current and lower root-mean-square (RMS) current. Within entire power range, compared with conventional DAB modulations, DAPM modes can achieve lowest RMS current, lowest peak current and widest ZVS ranges. Finally, a DAB-based prototype is established to verify effectiveness of proposed DAPM.