Modulation Operation Research Articles

(Invited) Recent Advances in the Research of Graphene Plasmonic Terahertz Laser Transistors

Electrons and holes in graphene behave as relativistic charged massless Dirac fermions due to the graphene unique gapless electronic band structure with a linear dispersion law. Dirac plasmons - the quanta of the plasma oscillation of the Dirac electrons - can dramatically enhance the interaction of terahertz (THz) photons with graphene. We have proposed an original current-injection graphene THz laser transistor, demonstrated single-mode THz laser oscillation at low temperatures [1-3], and discovered and demonstrated the THz giant gain enhancement effect by the graphene Dirac plasmons [4-8]. However, further breakthroughs are needed to realize room-temperature high-intensity THz lasing and ultrafast modulation operation for the next generation wireless 6G and 7G communications. In this paper, we will present new ideas on the operating principle and device structures of the THz graphene plasmonic laser transistors with a high radiation intensity and ultrafast modulation capability operating at room temperature.To dramatically improve the quantum efficiency and gain, we utilize the Coulomb drag effect in lateral n+ - i – n - n+ graphene diode/transistor structures with the ballistic injection of the graphene Dirac fermions [9-11]. Such injection strongly modifies the current-voltage characteristics producing “plasmonic gain” in the THz frequency range applicable for THz oscillations and amplifications. This phenomenon is associated with the specifics of the ballistic electron scattering on quasi-equilibrium electrons in graphene. Depending on the device structural parameters (in particular, the gated region length and its electron Fermi energy), the graphene diode/transistor structures can exhibit either S-shaped or monotonic current-voltage characteristics [9]. In the former case, the resulting hysteresis and current filamentation effects can be used for the implementation of the voltage-switching devices. The feedback between the amplified dragged electrons current and the injected ballistic electrons current can lead to the negative THz dynamic conductivity. The self-excitation of the THz plasma oscillations in the gated region enables the realization of the graphene transistor-based sources of THz radiation [11].To realize ultrafast modulation of lasing intensity/phase, we introduce actively controlling the parity and time-reversal (PT) symmetry [12] of the graphene Dirac plasmons (GDPs) in the dual-grating-gate graphene-channel field effect transistor (DGG-GFET) nanostructures for the ultrafast modulation of the lasing intensity and phase. [13]. The PT symmetry is expressed by a pair of complementary gain and loss elements. This gain–loss balance leads to the exceptional points at the real frequency axis in the exact PT-phase resulting in the extraordinary frequency response of “unidirectionality” [14]. The DGG-GDP metasurface, which consists of a unit cell comprising a pair of gain and loss regions and its periodical arrangement, promotes the GDP instability. The PT symmetry can be controlled (to be held or broken) by altering the gate or drain bias voltages. Our numerical simulations showed that the laser cavity Q values can be dynamically controllable in a DGG-GDP transistor structure [6] demonstrating 100-Gbit/s-class ultrafast modulation capabilities [13].The authors thank A.A. Dubinov, D. Yadav, T. Watanabe, T. Suemitsu, W. Knap, V. Kachorovskii, and V.V. Popov for their contributions. This work was supported by JSPS-KAKENHI No. 21H04546, and No. 20K20349, Japan. V. Ryzhii, M. Ryzhii, and T. Otsuji, J. Appl. Phys. 101, 083114 (2007).T. Otsuji et al., IEEE J. Sel. Top. Quantum Electron. 19, 8400209 (2013).D. Yadav et al., Nanophoton. 7, 741-752 (2018).A.A. Duvinov el al., J. Phys.: Cond. Matters 23, 145302 (2011).T. Watanabe et al., New J. Phys. 15, 075003 (2013).Y. Koseki et al., Phys. Rev. B 93, 245408 (2016).S. Boubanga-Tombet et al., Phys. Rev. X 10, 031004 (2020).S. Boubanga-Tombet et al., Front. Phys. 9, 726806 (2021).V. Ryzhii et al., Phys. Rev. Appl. 16, 014001 (2021).V. Ryzhii et al., Appl. Phys. Lett. 119, 093501 (2021).V. Ryzhii et al., Physica Status Solidi A 218, 2100535 (2021).M.-A. Miri and A. Alu, Science 363, eaar7709 (2019).T. Otsuji et al., Nanophoton. under review.H. Ramezani and T. Kottos, Phys. Rev. A 82, 04383 (2010). Figure 1

Electrochemical modulation of pore structure inside structural supercapacitor solid electrolyte

Solid electrolytes with a large number of pores can replace liquid electrolytes to effectively avoid liquid leakage as well as undertake electrochemical-mechanical functions. However, the influences of pore structure inside solid electrolytes on load transfer and capacitive nature of corresponding structural supercapacitors are usually contradictory. Here, electrochemical modulation is firstly applied to tune the pore structure of polyacrylic acid (PAA) cement electrolyte to solve the trade-off. Hierarchical network pore structure inside PAA cement electrolyte optimizes to an ideal state with an electrochemical modulation operation voltage of 1 V, achieving synchronous improvements in capacitance (increasing by 90%) and compressive strength (increasing by 20%) of corresponding structural supercapacitor. The important contribution of pore structure inside PAA cement electrolyte to capacitive nature of corresponding structural supercapacitor is introduced through experiments and molecular dynamics simulations. As the porosity, specific surface area and average pore size of pore structure inside PAA cement electrolyte increase to critical values, the capacitance of corresponding structural supercapacitor enhances to the maximum value. These surprising results provide a blueprint for optimizing pore structure inside structural supercapacitor solid electrolyte via electrochemical modulation.

Research on the Primary Frequency Modulation Operation of 650MW Nuclear Power Steam Turbine Unit in China

Research on the Primary Frequency Modulation Operation of 650MW Nuclear Power Steam Turbine Unit in China

Discrete vector-valued nonuniform Gabor frames

Gabor frames have interested many mathematicians and physicists due to their potential applications in time-frequency analysis, in particular, signal processing. A Gabor system is a collection of vectors which is obtained by applying modulation and shift operators to non-zero functions in signal spaces. In many applications, for example, signal processing related to Gabor systems, the corresponding shifts may not be uniform. That is, the set associated with shifts may not be a group under usual addition. We analyze discrete vector-valued nonuniform Gabor frames (DVNUG frames, in short) in discrete vector-valued nonuniform signal spaces, where the indexing set associated with shifts may not be a subgroup of real numbers under usual addition, but a spectrum which is based on the theory of spectral pairs. First, we give necessary and sufficient conditions for the existence of DVNUG Bessel sequences in discrete vector-valued nonuniform signal spaces in terms of Fourier transformations of the modulated window sequences. We provide a characterization of DVNUG frames in discrete vector-valued nonuniform signal spaces. It is shown that DVNUG frames are stable under small perturbation of window sequences associated with given discrete vector-valued nonuniform Gabor systems. We observed that the arithmetic mean sequences associated with window sequences of a given DVNUG frame collectively constitute a discrete nonuniform Gabor frame. Finally, we discuss an interplay between window sequences of DVNUG systems and their corresponding coordinates.

A Novel Multisensor Detection System Design for Low Concentrations of Volatile Organic Compounds

In this article, we investigate a novel multisensor odor detection system (electronic nose) for low-concentration volatile organic compounds (VOCs). In order to break through the limitation for detecting low concentration VOCs, we design a conformal symmetric preconcentration unit structure based on the finite element method. A typical application for exhaled breath is developed to investigate the proposed scheme. The designed preconcentration system can increase the concentration of the concentrated substance, so that the sensor can detect it. Besides, we choose the alveolar gas at the bottom of the human lung, which can better represent the health status of the human body, to carry out the effectiveness test of the system. In order to combine the gas acquisition system with the preconcentration system, this article further designs a cost-effective alveolar gas collection device by a doubled adaptive pulsewidth modulation (PWM) operation. Finally, the effectiveness of the preconcentration system is judged by the detection results of gas chromatography-mass spectrometry (GC-MS). We also use the classical algorithm to classify lung cancer and nonlung cancer patients, which proves the effectiveness of our proposed integrated design system and shows the potential of practical application of the system.

Reflection sensitivity of InAs/GaAs epitaxial quantum dot lasers under direct modulation

This paper reports on the reflection sensitivity under direct modulation operation of a 1.3 μm InAs/GaAs quantum dot laser that is epitaxially grown on silicon. The quantum dot laser exhibits a high tolerance to back reflections with low error transmission at 6 Gbps. This study paves the way for developing directly modulated isolator-free photonic integrated circuits based on quantum dot lasers.

112 Gb/s PAM-4 Silicon Photonics Receiver Integrated With SiGe-BiCMOS Linear TIA

We have developed a silicon photonics receiver integrated with a SiGe-BiCMOS linear transimpedance amplifier (TIA) using the flip-chip bonding technology to assist in resolving the I/O bottleneck problem in inter-chip data communication. The proposed device demonstrated optical 112 Gb/s four-level pulse amplitude modulation (PAM-4) operations and clear eye openings without any equalization for the pseudorandom binary sequence <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2^{\mathbf {15}}$ </tex-math></inline-formula> – 1 signal. The 3 dB bandwidth and transimpedance gain were designed to be 37.1 GHz and 60.1 dB <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\Omega } $ </tex-math></inline-formula> , respectively, at a supply voltage of 3.3 V. The consumption current of the linear TIA was 95.1 mA, and it resulted in a power consumption of 314 mW (2.8 pJ/bit). A linear TIA circuit is a key technology for PAM-4 operation; therefore, we discussed the linearity of our receiver response through eye diagrams and simulation. The measured eye diagrams agreed with the simulation results, and the proposed device maintained a linear response for up to 450 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\mu }\text{A}_{\mathbf {p-p}}$ </tex-math></inline-formula> input current. In addition, its operation rate of 112 Gb/s is the highest operation rate reported for a silicon photonics PAM-4 receiver based on flip-chip 3D integration with a germanium photodetector and a SiGe-BiCMOS linear TIA.

Mid-infrared Integrated Electro-optic Modulator Operating up to 225 MHz between 6.4 and 10.7 μm Wavelength

Mid-infrared spectroscopy is essential for identifying molecular species, while related electro-optic modulators are crucial for signal-to-noise enhancement via synchronous detection. Therefore, the development of integrated modulators is expected to have a major impact in compact and widespread sensing applications. In this work, we experimentally demonstrate a broadband integrated electro-optic modulator, based on a graded-index SiGe photonics platform and free-carrier plasma dispersion effect. Optical modulation is reported from 6.4 to 10.7 μm wavelength, showing an operational frequency up to 225 MHz. These results pave the way for the development of multimolecule on-chip spectroscopic systems, operating at the longest mid-infrared wavelengths.

A new Secure Speech Communication Scheme Based on Hyperchaotic Masking and Modulation.

This paper presents a new, effective, simple, and more secure speech communication technique based on the combination of hyperchaotic masking and modulation. One hyperchaotic system is used for both masking and modulation operations. Speech communication techniques based on only chaotic masking have weak resistance to several attacks. So, further encryption is applied using chaotic modulation. Second-level encryption has enhanced the security of speech communication, as evidenced by the performance metrics. The encryption correlation coefficient between the original signal and the encrypted signal after chaotic masking is 0.0101. However, the correlation coefficient has become 0.0007 after the second level of encryption. Again, the speech signal segmental spectral signal to noise ratio (SSSNR) is -32.5160 dB after the first level of encryption, but the SSSNR becomes - 47.2612 dB after performing chaotic modulation in the second level of encryption. The decryption process is achieved successfully and the original speech signal is retrieved. The required synchronization is performed using an active controller.

A 100 Gbaud On-off-Keying Silicon-Polymer Hybrid Modulator Operating at up to 110°C

We demonstrate 100-Gbaud on-off-keying (OOK) transmission driven at a low voltage using an electro-optic (EO) polymer modulator combined with a silicon Mach-Zehnder interferometer waveguide. Various types of organic- and polymer-based modulators have been reported to perform efficient EO modulation and high-speed data transmission at over 100 Gbaud. However, there are critical concerns regarding the practical application of polymer devices in terms of environmental stability. In particular, long-term thermal storage and stability during operation require improvements before EO polymer modulators can be applied in practical systems. We have developed an EO polymer with enhanced thermophysical stability and used it to fabricate an efficient EO polymer modulator. In this study we extend our earlier work on high-speed EO polymer modulators by performing fiber-link 100-Gbaud OOK transmission at various operating temperatures. A thermal stability test revealed that the EO polymer modulator can survive high-temperature exposure up to 110°C. Error-free signal transmissions over a distance of 2.0 km was successfully demonstrated with a driving voltage of 1.9 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> and a bit error rate below the 7% overhead forward error correction threshold. The driving voltage, bandwidth, bit error rate, and fiber-link performance of the device are presented.

Frames over finite fields: Basic theory and equiangular lines in unitary geometry

We introduce the study of frames and equiangular lines in classical geometries over finite fields. After developing the basic theory, we give several examples and demonstrate finite field analogs of equiangular tight frames (ETFs) produced by modular difference sets, and by translation and modulation operators. Using the latter, we prove that Gerzon's bound is attained in each unitary geometry of dimension d=22l+1 over the field F32. We also investigate interactions between complex ETFs and those in finite unitary geometries, and we show that every complex ETF implies the existence of ETFs with the same size over infinitely many finite fields.

Comparative analysis of leakage current suppression capability of forward‐clamped and reverse‐clamped H10 three‐phase inverters

Non-isolated inverters have the disadvantage of large leakage current, which will damage the equipment and personal safety. In order to solve this problem, this paper proposes two H10 three-phase inverter topologies named forward-clamped and reverse-clamped H10 inverters. Each of the topologies is composed of two DC bus switches, a clamping circuit and a traditional three-phase inverter, but the clamping method of these two topologies is different. A general control strategy combining carrier modulation and logic operation for these two topologies are proposed. The control strategy allows the common-mode voltage of these two topologies to vary between one third and two thirds of the DC bus voltage, but the frequency of the common-mode voltage of the reverse-clamped inverter is three times that of the forward-clamped inverter. The loop impedance of the reverse-clamped inverter increases significantly at high frequency, so the leakage current suppression capability is better. Simulation and experiment platforms of the inverter systems are built. The obtained results verify the correctness of the theoretical analysis.

A numerical model of a linear compressor for household refrigerator

Linear compressor is more efficient than conventional reciprocating compressor due to the absence of a crank mechanism. It can also realize capacity modulation, compactness and oil-free operation. A comprehensive numerical model of a linear compressor consisting of a thermodynamic model describing the in-cylinder pressure and temperature, a mechanical dynamics model describing movement the piston and valves and an electrical model describing the interaction of the voltage, current and back electromotive force of the linear motor was established to predict the compressor performance and to help achieve inherent capacity modulation. Experiments were conducted to validate the model using a prototype moving magnet linear compressor and remarkable accuracy is obtained. The measured and predicted piston displacement, current and shaft force agree well with the maximum error less than 10%. The predicted power factor, power consumption, stroke, mass flow rate and CoP show mean absolute percentage errors of 0.8%, 13.3%, 3.9%, 9.2% and 9.0%, respectively. As predicted, the resonant frequency can lead to lowest power consumption as well as the highest power factor and motor efficiency. At pressure ratio of 3.0, when the piston stroke increases by 1 mm, the mass flow rate increases by 0.66 g/s while the cooling capacity increases by 77.2 W. This can indicate the possibility of inherent capacity modulation.

Dependence of the integral characteristics of a nematic light modulator on the physical parameters of a liquid crystal

In the present work, the effect of physical constants of an LC material on the integral characteristics of a modulator operating in a waveguide mode in an LC structure with a twist angle of 270 and antisymmetric boundary conditions in the working cell was studied using the method of computer simulation. It is shown that, under antisymmetric boundary conditions, the small value of the total response time of the LC modulator is due to the absence of a “backflow” in the LC cell and the role of only half of the LC working gap thickness in the dynamics of switching between two states in such a device. In addition, it was found that in order to simultaneously achieve high contrast ratios and a short total response time of the device, it is necessary to choose an LC material with a high value of its dielectric anisotropy. In this case, there is an optimal set of elasticity constants for the LC material, which simultaneously realizes a high contrast ratio and a short total response time of the modulator.

Parametric Doppler correction analysis for wayside acoustic bearing fault diagnosis

Wayside acoustic system plays a crucial role in monitoring and diagnosing the status of train wheel bearings. However, due to the signal distortion caused by Doppler effect, the diagnosis accuracy will be seriously disturbed. In this manner, this paper proposes a model-driven Doppler distortion self-tuning method in theory, named as parametric Doppler correction analysis (PDCA). Different from traditional methods, such as instantaneous frequency tracking and Doppler distortion sparse representation, the proposed method aims to abstractly construct a physical model of acoustic signal distortion propagation based on Morse acoustic theory, where the acoustic forward propagation model and reverse reconstruction model are simultaneously built. The scheme consists of four basic steps. Firstly, the physical model with amplitude modulation operator and frequency shift operator is described for the distortion process. Secondly, the pseudo transition signal with the characteristics of energy accumulation and no distortion is obtained via a construction of frequency rearrangement operator and amplitude demodulation operator. Then, pseudo Doppler correction (PDC) is presented to solve the frequency distortion of the received signal, where a high energy accumulation for frequency distribution is designed as optimization function. Especially, quasi Newton algorithm L-BFGS is used to realize the adaptive learning for distortion parameters. Finally, through time-domain interpolation resampling (TIR) technique, the corrected signal can be analytically reconstructed with the optimal parameters. Applying the PDCA scheme to simulated signals and experimental signals, its validity is verified. The comparison with the instantaneous frequency ridge extraction approach further indicates the proposed model-driven method can reach a more accurate correction result in a faster and adaptive process.

Osmium Nanoparticles-Polypropylene Hollow Fiber Membranes Applied in Redox Processes.

Composite membranes play a very important role in the separation, concentration, and purification processes, but especially in membrane reactors and membrane bioreactors. The development of composite membranes has gained momentum especially through the involvement of various nanoparticles, polymeric, oxide, or metal, that have contributed to increasing their reactivity and selectivity. This paper presents the preparation and characterization of an active metal nanoparticle-support polymer type composite membrane, based on osmium nanoparticles obtained in situ on a polypropylene hollow fiber membrane. Osmium nanoparticles are generated from a solution of osmium tetroxide in tert-butyl alcohol by reduction with molecular hydrogen in a contactor with a polypropylene membrane. The composite osmium-polypropylene hollow fiber obtained membranes (Os-PPM) were characterized from the morphological and structural points of view: scanning electron microscopy (SEM), high resolution SEM (HR-SEM), energy dispersive spectroscopy analysis (EDAX), X-ray diffraction analysis (XRD), Fourier transform Infrared (FTIR) spectroscopy, thermal gravimetric analysis, and differential scanning calorimetry (TGA, DSC). The process performance was tested in a redox process of p-nitrophenol and 10-undecylenic (10-undecenoic) acid, as a target substance of biological or biomedical interest, in solutions of lower aliphatic alcohols in a membrane contactor with a prepared composite membrane. The characteristics of osmium nanoparticles-polypropylene hollow fiber membranes open the way to biological and biotechnological applications. These membranes do not contaminate the working environment, operate at relatively low temperatures, provide a large contact area between reactants, allow successive oxidation and reduction operations in the same module, and help to recover the reaction mass by ultrafiltration. The results obtained show that the osmium-polypropylene composite membrane allows the reduction of p-nitrophenol or the oxidation of 10-undecylenic acid, the conversion depending on the concentration in the lower aliphatic alcohol, the nature of the lower aliphatic alcohol, and the oxidant or reducing flow through the membrane contactor.

Windowed fractional Fourier transform on graphs: Properties and fast algorithm

A key challenge in the field of graph signal processing is to design proper transform methods to extract valuable information from signals on weighted graphs. This paper first defines convolution, translation and modulation operators in graph fractional domain, and proposes windowed graph fractional Fourier transform (WGFRFT). Related properties are proved. Then, a fast algorithm of WGFRFT is designed to increase flexibility. The robustness and superiority of the fast algorithm are verified via simulations with synthetic signals on graphs. Finally, an application to graph clustering is presented to show the practicability of WGFRFT.

Operation Design of Reaction Crystallization Using Homogeneity Evaluation for the Quality Improvement of Agglomerated Crystalline Particles

In the quality control of crystalline particles, the uniformity of the distribution of each characteristic, such as size and shape, is important. In particular, the problem in reaction crystallization is that the comprehensive uniformity of characteristic distributions is frequently reduced by the agglomeration phenomena. In this study, we designed an operation method to improve the comprehensive uniformity in a liquid–liquid reaction crystallization by evaluating the dynamic variation in the uniformity of particle size and crystal shape using homogeneity. The homogeneity of final particles increased when the supersaturation was lowered by intermittent operation with inner seed production. Since the ratios of the uniformities of particle sizes and crystal shapes constituting homogeneity varied dynamically, the intermittent operation was designed by focusing on individual uniformities. The uniformity of particle size for the final particles was increased via modulation operation using reverse addition for the dissolution of the microparticles. In the growth stage after the reverse addition, the uniformity of the shape of the final particles was increased by raising the number of times of adding solution for decreasing the supersaturation. In addition, we proposed suitable addition methods to improve comprehensive uniformity by controlling uniformity constituting homogeneity at each stage of intermittent operation.

DC Bus Voltage Regulation Strategy in Maritime DC Power System for Minimized Converter Loss

In a maritime dc power system, the rectified dc-bus voltage of a permanent magnet synchronous generator is generally regulated by the pulsewidth modulation (PWM) operation of an active ac/dc converter. This article proposes a dc bus voltage regulation strategy exploiting the six-step operation. Under the six-step operation, the switching loss of the converter can be significantly reduced, compared to the PWM operation. Moreover, due to the higher modulation index and the less flux-weakening current of the six-step operation, the conduction loss can also be reduced. By employing diode rectification mode at light load, the conduction loss induced by the non-negligible ripple current of the six-step operation could be minimized. This article implements a controller for the proposed dc bus voltage regulation strategy and verifies its validity with simulation and experimental setup. According to the simulation and the experimental test, the converter efficiency at the rated load is enhanced by 0.6% and 0.4%, and the converter loss is reduced by up to 70% and 19%, respectively.

High Baud Rate Transmission With Silicon Photonic Modulators

We review high baud rate operation of silicon photonic modulators with emphasis on short-reach and metro-haul applications. The current status of both devices and digital signal processing are discussed. The basic design of a typical carrier-depletion-based dual-drive traveling-wave Mach-Zehnder modulator (TW-MZM) is studied by simulation. Based on an all-silicon TW-MZM, we report the transmission experiments of high baud rate single sideband 4-ary pulse amplitude modulation (PAM-4) signals with linear equalization and artificial neural network based equalization, respectively. Our work indicates all-silicon modulators can address the requirements of future optical communication systems operating at 100 Gbaud.