Phase Mismatch Research Articles

An Improved Phase Noise Reduction in Millimeter-Wave FBMC Systems

The next generation mobile network needs to have a spectrum above the 30 GHz radio band. The 5G system is a promising technology for future communication systems. It has been used in Device-to-Device (D2D) communications, IoT, Machine type communications (MTC), and wireless backhaul. The 5G is expected to have speeds of hundreds of times and satisfy the requirements of larger traffic density, low latency, connective density, higher capacity & reliability, data rate, super high mobility, etc. It is expected to have applications such as HD video, virtual reality & augmented reality, online games, and cloud desktops. For this, Millimeter wave (Mmwave) has been used for fifth-generation mobile networks. The millimeter wave has a frequency range from 30 to 300 GHz. When the usage of frequency is above 60 GHz, the band will acquire RF impairments such as PAPR, Phase noise, non-linearity, and phase and quadrature timing mismatch (IQTM). This article shows the Phase noise reduction in MIMO FBMC systems using Extended Kalman filter techniques.

Vortex light bullets in rotating Quasi-Phase-Matched photonic crystals

We present a methodology for the generation of stable vortex light bullets (LBs) in rotating Quasi-Phase-Matched (QPM) photonic crystals with quadratic nonlinearity. The photonic crystal is designed with a checkerboard structure, which is feasible to realize by using contemporary technological advancements. Within this framework, square- and rhombus-shaped LBs are observed, both of which are constructed as four-peak vortex mode. The control parameters include the effective phase mismatch, power, rotating frequency, and the size of checkerboard cells. These parameters play key roles in determining the distribution and stability domains of vortex LBs. In contrast to the stable vortex solitons observed in two-dimensional (2D) quadratic systems, the LBs investigated in the 3D rotating system exhibit narrower stability domains within the system’s parameter space. The rotating frequency results in the transition of LBs from quadrupole to traditional vortex modes. Potential applications of this research lie in the field of optical communications and information processing.

Topological polarization beam splitter based on directional coupling between asymmetric valley photonic crystal waveguides.

Compared with symmetric directional couplers (DCs), asymmetric DCs constructed by two or over two different parallel waveguides offer a more flexible structure and allow for easier expansion of mode channels. In this Letter, we propose a kind of asymmetric topological DC based on two different valley photonic crystal waveguides (VPCWs). According to the coupled-mode theory, phase matching induces the complete coupling for the guide modes of two different VPCWs, whereas significant phase mismatching indicates no coupling occurs. Furthermore, the asymmetric topological DCs exhibit backscattering immunity and anti-disturbance robustness owing to the topological edge states (TESs), which greatly improve the performance of asymmetric DCs. We further design a new, to the best of our knowledge, kind of topological polarization beam splitter (TPBS) at the communication wavelength of 1550 nm by ensuring that the transverse electric mode satisfies the phase matching condition, while the transverse magnetic mode is phase-mismatched. The simulated results demonstrate that the proposed TPBS exhibits highly effective polarization separation and is robust against defects. This design holds significant potential for applications in optical communication systems.

Transceiver impairment robust and joint monitoring of PDL, DGD, and CD using frequency domain pilot tones for digital subcarrier multiplexing systems

Optical performance monitoring is vital for enabling dynamically reconfigurable optical networks. This paper introduces a monitoring scheme that is robust to transceiver impairments for coherent digital subcarrier multiplexing (DSCM) systems that simultaneously monitors polarization-dependent loss (PDL), differential group delay (DGD), and chromatic dispersion (CD). In the proposed scheme, a pair of frequency domain pilot tones (FPTs) are inserted into the X and Y polarizations of the transmitted dual-polarization signal. Both the signal and the FPTs endure identical channel impairments during fiber transmission. At the receiver side, the transmitted FPTs are extracted to monitor the channel impairments. We begin by establishing a simplified system model using a single frequency tone to analyze the effects of system impairments on the frequency domain pilots. Based on this model, CD, PDL, and DGD are jointly and accurately estimated. In addition, the influences of temporal, amplitude, and phase mismatches between in-phase (I) and quadrature (Q) components of transceivers on channel impairment monitoring are completely eliminated. This achieves a channel impairment monitoring scheme that is robust to transceiver impairments. Experimental verification shows that the proposed scheme can jointly and accurately estimate a wide range of CD, PDL, and DGD. Additionally, the proposed monitoring scheme demonstrates strong robustness against transceiver impairments, rapid polarization fluctuations, and amplified spontaneous emission (ASE) noise.

Generating first-order optical vortex beams by photonic crystal slabs

Optical vortices, which are beams with helical wavefronts and spiral phase mismatches, have garnered considerable attention in various fields. In this study, we theoretically proposed and experimentally implemented a simple method for generating first-order optical vortices. To generate first-order vortex beams using the polarization field in the momentum space of photonic crystal slabs, topological half charges are required. We propose a method to divide the polarization vortex in the momentum space by breaking symmetry, which results in Dirac points or circularly polarized points. This approach enables the transformation of topological integer charges into topological half-integer charges, thereby facilitating the generation of first-order vortex beams. This approach extends the application of bound states in continuum and topological photonics.

Characterizing electric fields in semiconductor devices: effect of second-harmonic light interference.

Characterizing electric fields in semiconductor devices using electric field-induced second-harmonic generation (EFISHG) has opened new opportunities for an advanced device design. However, this new technique still has challenges due to the interference between background second-harmonic generation (SHG) and EFISHG generated light. We demonstrate that interference effects can effectively be eliminated during EFISHG measurements by focusing the laser from the transparent substrate side of a GaN PN diode, enabling straightforward quantitative electric field analysis, in contrast to PN junction interface side measurements. A model based on wave generation and propagation is proposed and highlights the incoherence between background SHG and EFISHG light. This incoherence may be attributed to the depth of focus of the incident laser and phase mismatch between incident and SHG light.

Ultra-broadband detection of coherent infrared pulses by sum-frequency generation spectroscopy in reflection geometry.

We have newly developed, to the best of our knowledge, a detection method for broadband infrared pulses based on sum-frequency generation spectroscopy in reflection geometry, which can avoid a restriction of the detection bandwidth originating from the phase mismatch that is inevitable for the upconversion in transmission geometry. Using a GaAs crystal, we successfully demonstrated the ultra-broadband detection of the infrared pulses generated from a two-color laser-induced air plasma filament in a region from 300 to 3300 cm-1. With the advantage of ultra-short infrared pulses, the present detection method holds promise for application to time-resolved, ultra-broadband vibrational spectroscopy.

Investigation of the role of yttrium sesquioxide nanoparticles on the properties of zinc oxide ceramics

In this work, zinc oxide (ZnO) ceramics were synthesized containing 0-5wt% of cubic yttrium sesquioxide (Y 2 O 3) nanoparticles with solid state sintering technique at 1150°C. The secondary phase of Y 2 O 3 did not enter into the crystalline zinc oxide. The Y 2 O 3 acts as an inhibitor of grain growth. The absorption of the free charge carriers by the Y 2 O 3 phase influences the infrared transmissions. The minimization of the phase mismatch while transferring the electric signal caused lower losses when Y 2 O 3 was added to the zinc oxide matrices. The presence of the cubic sesquioxide at the grain boundary contributes to the interfacial polarization at lower frequencies when an alternating field is applied to the ceramics. These properties are anticipated to show a wider range of physical, optical and dielectric properties of ZnO: Y ceramics for optoelectronic applications.

Dispersion mismatch correction for evident chromatic anomaly in low coherence interferometry.

The applications of ultrafast optics to biomedical microscopy have expanded rapidly in recent years, including interferometric techniques like optical coherence tomography and microscopy (OCT/OCM). The advances of ultra-high resolution OCT and the inclusion of OCT/OCM in multimodal systems combined with multiphoton microscopy have marked a transition from using pseudo-continuous broadband sources, such as superluminescent diodes, to ultrafast supercontinuum optical sources. We report anomalies in the dispersion profiles of low-coherence ultrafast pulses through long and non-identical arms of a Michelson interferometer that are well beyond group delay or third-order dispersions. This chromatic anomaly worsens the observed axial resolution and causes fringe artifacts in the reconstructed tomograms in OCT/OCM using traditional algorithms. We present DISpersion COmpensation Techniques for Evident Chromatic Anomalies (DISCOTECA) as a universal solution to address the problem of chromatic dispersion mismatch in interferometry, especially with ultrafast sources. First, we demonstrate the origin of these artifacts through the self-phase modulation of ultrafast pulses due to focusing elements in the beam path. Next, we present three solution paradigms for DISCOTECA: optical, optoelectronic, and computational, along with quantitative comparisons to traditional methods to highlight the improvements to the dynamic range and axial profile. We explain the piecewise reconstruction of the phase mismatch between the arms of the spectral-domain interferometer using a modified short-term Fourier transform algorithm inspired by spectroscopic OCT. Finally, we present a decision-making guide for evaluating the utility of DISCOTECA in interferometry and for the artifact-free reconstruction of OCT images using an ultrafast supercontinuum source for biomedical applications.

Wideband N-Path-Based Phased-Array Receiver With Gain and Phase Mismatch Calibration

Wideband N-Path-Based Phased-Array Receiver With Gain and Phase Mismatch Calibration

Hybrid Coupler Used as Tunable Phase Shifter Based on Varactor Diodes.

This paper describes the design of a hybrid coupler with a continuously variable output phase difference. This is achieved by using reconfigurable transmission lines with electrically tunable lengths controlled by two biasing voltages through varactor diodes placed across the coupler branches. The design of the coupler is based on the quadrature hybrid structure for the case where the output phase difference is 90° and on the asymmetric structure for the other cases. The proposed coupler can achieve a tunable output phase difference from 52° to 128°, while keeping a coupling coefficient of -3 dB (± 0.5 dB) over the entire desired frequency band. To validate the simulated results, a prototype working at 3.5 GHz was fabricated and tested. The measurement results show good correspondence with the simulation results, especially when the output phase difference is 90°, while a phase mismatch of less than 7° was observed for the other cases. The presented coupler would be a great asset for antenna feeding arrays, especially the Butler matrix.

Характеристики обнаружения когерентной системы при рассогласовании квадратурных каналов

Introduction – The operation of an adaptive coherent detection system is considered. The structure of a processing device is presented, containing a series-connected shaper of quadrature signal components that convert high-frequency input radio signals to video frequency, an adaptive multi-channel coherent storage device with threshold devices. Goal – To study the influence of amplitude and phase mismatches of quadrature channel parameters, which are inevitable in practice, on the operation of an adaptive coherent detection system. Formulation of the problem – Determine the spectral-correlation characteristics of the processed signals when the parameters of the quadrature channels are mismatched. Assess the influence of amplitude and phase deviations of the parameters of quadrature channels on the characteristics of a coherent detection system. Method – The complex variable method is used, in which the input high-frequency signals are represented at the video frequency by a pair of complex conjugate real components, shifted in phase by ninety degrees. Results – A model of the processed signal is presented at the video frequency, taking into account possible mismatches in the parameters of quadrature channels in practice. Expressions are obtained and graphs of the spectral density of the complex signal are plotted separately for the amplitude and phase mismatch of the quadrature channels. It is shown that the mismatch of quadrature channels leads to the appearance in the spectrum of the output signal of phase detectors of a component at a frequency that is the mirror frequency of the signal, which leads to an increase in the probability of false detection. The results of calculations of the probability of false detection of a signal depending on the deviation of the transmission coefficients of the quadrature channels and the phase mismatch of the reference voltages of the quadrature channels are presented. Conclusion – The significant influence of amplitude and phase mismatches of the parameters of quadrature channels on the spectral-correlation characteristics of the complex signal is shown. The mismatch of the parameters of the quadrature channels leads to deterioration in the detection characteristics of the coherent processing system. The research methodology used allows us to develop requirements for the quality of tuning quadrature channels.

Kinetic-magnetohydrodynamic hybrid simulation of infernal modes in circular tokamak plasmas with effects of kinetic thermal ions

Effects of the kinetic thermal ions (KTIs) on ideal infernal modes and resistive infernal modes have been investigated by using magnetohydrodynamic (MHD) simulation without KTIs and kinetic-MHD hybrid simulation with KTIs. For the ideal infernal modes, the pressure profile is significantly flattened at the saturated state for both the models with and without the KTIs. As the beta value decreases, the ideal infernal modes are stabilized while the resistive infernal modes are still unstable. For the resistive infernal modes, while the saturated pressure profile is significantly flattened in the MHD simulation without KTIs, the pressure profile is not flattened at the saturated state in the kinetic-MHD hybrid simulation with KTIs. The suppression of the saturation level by the effects of the KTIs results from the phase mismatch between the radial velocity and perturbed pressure mode structures. This indicates that KTIs play an essential role for the suppression of pressure profile flattening due to slowly growing resistive MHD instabilities.

Heterophase Intermetallic Compounds for Electrocatalytic Hydrogen Production at Industrial-Scale Current Densities.

Heterophase nanomaterials have sparked significant research interest in catalysis due to their distinctive properties arising from synergistic effects of different components and the formed phase boundary. However, challenges persist in the controlled synthesis of heterophase intermetallic compounds (IMCs), primarily due to the lattice mismatch of distinct crystal phases and the difficulty in achieving precise control of the phase transitions. Herein, orthorhombic/cubic Ru2Ge3/RuGe IMCs with engineered boundary architecture are synthesized and anchored on the reduced graphene oxide. The Ru2Ge3/RuGe IMCs exhibit excellent hydrogen evolution reaction (HER) performance with a high current density of 1000 mA cm-2 at a low overpotential of 135 mV. The presence of phase boundaries enhances charge transfer and improves the kinetics of water dissociation while optimizing the processes of hydrogen adsorption/desorption, thus boosting the HER performance. Moreover, an anion exchange membrane electrolyzer is constructed using Ru2Ge3/RuGe as the cathode electrocatalyst, which achieves a current density of 1000 mA cm-2 at a low voltage of 1.73 V, and the activity remains virtually undiminished over 500 h.

Quadratic phase mismatch in multisoliton interferograms based on time-stretched dispersive Fourier transformation

Quadratic phase mismatch in multisoliton interferograms based on time-stretched dispersive Fourier transformation

Effect of Phase Shifting on Real-Time Detection and Classification of Power Quality Disturbances

Power quality improvement and Power quality disturbance (PQD) detection are two significant concerns that must be addressed to ensure an efficient power distribution within the utility grid. When the process to analyze PQD is migrated to real-time platforms, the possible occurrence of a phase mismatch can affect the algorithm’s accuracy; this paper evaluates phase shifting as an additional stage in signal acquisition for detecting and classifying eight types of single power quality disturbances. According to their mathematical models, a set of disturbances was generated using an arbitrary waveform generator BK Precision 4064. The acquisition, detection, and classification stages were embedded into a BeagleBone Black. The detection stage was performed using multiresolution analysis. The feature vectors of the acquired signals were obtained from the combination of Shannon entropy and log-energy entropy. For classification purposes, four types of classifiers were trained: multilayer perceptron, K-nearest neighbors, probabilistic neural network, and decision tree. The results show that incorporating a phase-shifting stage as a preprocessing stage significantly improves the classification accuracy in all cases.

Dynamics of a vibrating screen with two motor-vibrators

A method for calculating a vibrating screen with two motor vibrators is proposed. The first part of the article is devoted to the issue of synchronizing the rotation of the rotors of both drives. Their opposite rotation creates a directed force passing through the center of gravity of the screen and perpendicular to the plane of the vibrator axes. The interaction of forces in this plane determines the phase mismatch of the rotation angles of the vibrators θ. An expression is obtained for determining the angle θ depending on the frequency of their rotation vibrators ω. It is shown that at ω > 100 rad/s, motor-vibrators operate in self-synchronizing mode. In the second part of the article a dynamic calculation of the screen was carried out. Linear vibrations in the vertical plane of symmetry of the screen and rotational vibrations around a perpendicular to this plane are investigated. The Lagrange equation of the second kind is compiled without considering inelastic resistances. They are considered at the last stage of the calculation in the form of the imaginary part of the complex modulus of elastic bonds. The amplitude-frequency characteristic of the screen was constructed considering the rotation mismatch angle of the vibrators θ. Stabilization of the oscillation amplitude at high frequencies is shown.

Optical to terahertz frequency conversion using near zero-index nonlinear hybrid waveguides

Terahertz communications has emerged as an excellent candidate for the next generation of wireless communication networks. Despite of significant advances, one still looks for a high-efficiency terahertz source using nonlinear optics, such as optical refraction and difference-frequency generation. Concurrently, recent years have witnessed significant progress in metamaterials-assisted nonlinear optical processes. In this study, we propose a theoretical approach using near zero-index nonlinear hybrid waveguides to realize a high generation efficiency of terahertz waves via on-chip difference-frequency generation. Remarkably, thanks to the simultaneous realization of near zero-index both at terahertz and telecom frequencies, such a nonlinear hybrid waveguide can overcome two major bottlenecks in the conversion from optical wave to terahertz waves: phase mismatch and weak nonlinear optical-terahertz waves interactions, resulting in a high conversion as 2.2 × 10−3W−1 just within the propagation length of several terahertz wavelengths. Our results demonstrate the feasibility of an on-chip terahertz source, offering unique properties such as high integration and ultra-low power consumption for terahertz communication systems.

Analysis of Phase Mismatch for Mercurous Bromide-Based Non-Collinear AOTF Design in Spectral Imaging Applications.

The spectral and spatial characteristics of Acousto-Optic Tunable Filters (AOTFs), such as a tuning curve, spectral resolution, angular aperture, and diffraction efficiency, are determined by the device's acousto-optic crystal configuration and piezoelectric transducer. For high-throughput spectral imaging applications, it is essential to enlarge the spectral bandwidth and angular aperture during the design phase of AOTFs. Thus, phase mismatch due to incident angle or wavelength was studied analytically using phase diagrams in this paper. Additionally, a performance parameter analysis model was established based on the use of mercurous bromide crystals for large angular aperture AOTF device design, and the impact of crystal and transducer design parameters on the spectral bandwidth and angular aperture was evaluated. This also experimentally validates the diffraction capability of AOTFs made from mercurous bromide crystal, which possess a broad spectral transmission ability ranging from visible to long-wave infrared.

The single-cycle biphotons generated by SPDC in chirped QPM PPKTP crystal

In this paper, we have studied the process of monochromatic pump light in linearly chirped Periodically Poled [Formula: see text] (PPKTP) nonlinear crystal to generate single-cycle biphotons under Quasi-Phase-Matching (QPM) conditions through a Spontaneous Parametric Down-Conversion (SPDC). A detailed analysis of the phase mismatching function reveals that in PPKTP crystals, for the proper frequency range, the phase mismatching [Formula: see text] is stable and relatively close to 0 due to the relatively stable refractive index, and therefore has a good phase matching effect. Even when the chirp rate becomes small, it is able to produce single-cycle biphotons due to the near-perfect phase matching. Of course, as the chirp rate increases, the frequency response range becomes wider, the temporal width is narrower, and the number of cycles is smaller.