Nonlinear Amplifier Research Articles

Principle and application of amplifier of fiber on fiber communication

As the most widely used and the most reliable way of communication in the world today, the development of optical fiber communication will inevitably affect the world. As an important component of fiber communication system, the development of fiber amplifier directly affects the development of fiber communication. The fiber amplifier is divided into semiconductor fiber amplifier, mixed with rare earth element fiber amplifier and nonlinear fiber amplifier. This paper aims to study the principle, function and equipment of the fiber optic amplifier. Some limitations and prospects for the future are also proposed.The principle, function and limitation of erbium-doped fiber amplifier are emphasized. It is a summary of the development of fiber amplifier in recent years, and it is convenient for other scholars to find and study the data of fiber amplifier. This paper summarizes the development of fiber amplifier in recent years, and explains the basic principles of fiber amplifier, so that other scholars to find the data of fiber amplifier, convenient for other scholars to study.

Designing an active electronically scanned array as part of onboard equipment of a high-speed radio communication channel

The active electronically scanned array being developed is designed to provide an all-weather high-speed radio communication channel “Spacecraft – Earth”. It is supposed to provide fast, inertia-free observation of space by swinging the antenna beam electrically, and, in fact, is a dynamic space-time filter of the spacecraft. The aim of the work is to identify the basic principles of functioning of the array as part of the spacecraft with inherent limitations in the mass-dimensional and energy characteristics of the onboard equipment and, at the same time, high requirements for the functional characteristics. This paper presents the calculation and the main results of designing an active electronically scanned array complying with the requirements for optimizing the parameters of the antenna system. To assess the effect of scanning on the phase characteristics of the chips, a nonlinear amplifier model was developed. A statistical analysis of the phase characteristics was carried out when the load resistance changed in accordance with the obtained distribution laws. When calculating the resulting directional pattern of the antenna array, destabilizing factors were taken into account in accordance with the results of the study of the prototypes of the antenna array being created. Phase errors were calculated, mainly determined by the errors of the terminal parts of the receiving paths. Measures were implemented to ensure the effect of such phase errors on the directional pattern of the array only on the far side lobes.

Milli-joule class femtosecond regenerative amplifier enabled by a narrowband fiber oscillator

We report on a room-temperature operated, Yb:CaF2 based, chirped-pulse regenerative amplifier system with a pulse duration of 300 fs and an output pulse energy of 2.0 mJ. A novel front end comprising a narrowband fiber oscillator and a nonlinear fiber amplifier is adopted to seed the regenerative amplifier. To achieve broadband spectral coverage for femtosecond pulse generation, nonlinear fiber amplification is implemented and spurs a 7-folded spectral extension. After the successive pulse stretching, spectral reshaping, regenerative amplifying, and compressing, optimum pulses with 300-fs duration and 6.7-GW peak power are obtained. Such intense pulses are capable of inducing laser filament at 0.4-mJ energy with a loosely focusing geometry. Our method demonstrates the potential of narrowband fiber lasers to enable femtosecond regenerative amplifiers and paves the way toward compact, robust, and cost-effective millijoule-class lasers.

Nonlinear mechanical behavior and stress amplification effect correction of thin plate welded structure considering initial deformation

With the continuous development of light weight of ships, thin plate welded structures are widely used in superstructure of large hull structures and high-speed boats. However, the thin-plate welded structure has a special nonlinear mechanical behavior because of its small stiffness, more complicated welding deformation. The nonlinear mechanical behavior of thin plate welded structure is mainly caused by large slenderness ratio and complex initial buckling deformation, which can be characterized and quantified by defining global deformation angle αG and local deformation angle αL. Because of the welding angle deformation and welding dislocation, there is obvious stress amplification effect at the welding corner, but the traditional stress amplification correction formula is only suitable for thick plate welding structure. Aiming at the nonlinear mechanical behavior and secondary bending moment effect of thin plate welded structure, an analytical model of thin plate welded structure with initial deformation is established by combining theoretical derivation and numerical method. The results show that the additional bending moment effect caused by local welding deformation angle cannot be ignored. Finally, combined with a series of fatigue tests, the additional bending moment caused by bending deformation and angular deformation of typical welded joints is analyzed, and the notch stress field and fatigue strength correction of thin plate welded structures with initial defects are realized.

Gain-managed nonlinear amplification of ultra-long mode-locked fiber laser.

In this study, we explored the gain-managed nonlinear (GMN) amplification of ultra-low repetition rate pulses in the range of less than 1 MHz. By seeding the developed 1040 nm ultralong fiber modelocked laser to the GMN amplifier, we achieved high gain and boosted the nonlinear pulse propagation effects. We demonstrated that GMN amplification of low repetition rate pulses provided amplification exceeding 32 dB and spectral broadening up to 91 nm at relatively low pump power levels. Achieving broadband 57 fs pulses with energy exceeding 55 nJ suggests that ultralong fiber lasers paired with GMN amplifiers can be effectively utilized as powerful tools for generating femtosecond broadband pulses at ultra-low repetition rates, with controllable spectral characteristics.

Combining observed linear basin amplification factors with 1D nonlinear site-response analyses to predict site response for strong ground motions: Application to Wellington, New Zealand

This study develops a method for estimating site amplification that combines instrumentally observed site-specific amplification factors with adjustment factors from nonlinear site-response analyses. This approach provides estimates of site response for large-strain motions based on observations and sophisticated nonlinear modeling. A database of weak-to-moderate intensity ground motions recorded in three basins of Wellington, New Zealand is used to study the observed site amplification. A subset of nine strong-motion stations was selected to perform nonlinear site-response analyses with scaled strong ground motions to assess the influence of nonlinearity on site amplification factors and demonstrate the approach. Different shear-wave velocity ( VS) profiles, constitutive models, and modeling approaches (e.g. one-dimensional (1D) site-response analyses vs empirical [Formula: see text]-based approaches) are used to quantify the sensitivity and modeling uncertainty in the nonlinear site-response analyses. It was found that for soft sites subjected to strong ground motions, there may be a decrease in spectral acceleration amplification factors for periods up to approximately 2 s, relative to the expected linear site response. For longer periods, there is little to no amplification from the effects of soil nonlinearity. However, at stiffer sites, which generally experience less basin amplification in observations, there may be moderate amplification at longer periods when nonlinearity is considered due to softening of the soil profile. Empirical ground-motion models were found to under-represent the observed amplification between basin sites and the nearby reference site, especially at intermediate to long periods, corresponding to resonant frequencies of these basin sites. In addition, the empirical nonlinear site amplification models ([Formula: see text]-based) were found to deviate from nonlinear analyses at large strains, where such models are poorly constrained due to such a limited number of observations.

Nonlinear effect amplification: Differential susceptibility of verbal overshadowing as a function of time to interference.

Nonlinear effect amplification: Differential susceptibility of verbal overshadowing as a function of time to interference.

Error Vector Magnitude as a Performance Standard for Antennas in the Millimeter-Wave Era: Part 2: Modeling, simulation, and measurement methods

The error vector magnitude (EVM) is a comprehensive measure of the amplitude and phase distortion of digitally modulated signals and a potential tool for characterizing the performance of active beamforming arrays, especially at millimeter-wave frequencies, because of the high level of integration and limited spacing between the radiating elements. A review of the EVM measurement process and fundamental principles for time-domain demodulation with a vector signal analyzer (VSA) and spectral correlation with a vector network analyzer (VNA) was presented in [1]. This article demonstrates how researchers have modeled and measured impairments from antenna and phased array signal transmission to characterize their influence on the EVM of single and multicarrier digital signals. It presents examples of simulation models and measurements of the distortion from ultrawideband (UWB) passive antenna transmission, power amplifier (PA) nonlinearities, and phased array beam squint and beam scan intersymbol interference (ISI). A brief survey of over-the-air (OTA) test ranges for EVM analysis is also provided. This overview of state-of-the-art EVM simulation and measurement methods is intended to help interested readers understand and enhance the EVM performance analysis methods applied to antennas and phased arrays in this new era of millimeter-wave communications.

Cooperative optical pattern formation in an ultrathin atomic layer

Spontaneous pattern formation from a uniform state is a widely studied nonlinear optical phenomenon that shares similarities with non-equilibrium pattern formation in other scientific domains. Here we show how a single layer of atoms in an array can undergo nonlinear amplification of fluctuations, leading to the formation of intricate optical patterns. The origin of the patterns is intrinsically cooperative, eliminating the necessity of mirrors or cavities, although introduction of a mirror in the vicinity of the atoms significantly modifies the scattering profiles. The emergence of these optical patterns is tied to a bistable collective response, which can be qualitatively described by a long-wavelength approximation, similar to a nonlinear Schrödinger equation of optical Kerr media or ring cavities. These collective excitations have the ability to form singular defects and unveil atomic position fluctuations through wave-like distortions.

Characterization of Site Amplification by a Parametric Study

ABSTRACT The reliability of V s30 and the performance of alternative time averaged shear wave velocities (V sz ) and shear wave travel times (T tz ) at various depths, z, were investigated for the estimation of site amplification and fundamental frequency (f 0) characterization by considering the linear and nonlinear soil behavior. The study revealed that alternative parameters performed better than V s30 and the best performing z parameters changed by switching from convex to concave theoretical profiles and by increasing ground motions. For a practical usage in site investigations, guidelines to estimate nonlinear soil amplification factor and fundamental frequency from the linear ones were presented.

Intracochlear overdrive: Characterizing nonlinear wave amplification in the mouse apex.

In this study, we explore nonlinear cochlear amplification by analyzing basilar membrane (BM) motion in the mouse apex. Through in vivo, postmortem, and mechanical suppression recordings, we estimate how the cochlear amplifier nonlinearly shapes the wavenumber of the BM traveling wave, specifically within a frequency range where the short-wave approximation holds. Our findings demonstrate that a straightforward mathematical model, depicting the cochlear amplifier as a wavenumber modifier with strength diminishing monotonically as BM displacement increases, effectively accounts for the various experimental observations. This empirically derived model is subsequently incorporated into a physics-based "overturned" framework of cochlear amplification [see Altoè, Dewey, Charaziak, Oghalai, and Shera (2022), J. Acoust. Soc. Am. 152, 2227-2239] and tested against additional experimental data. Our results demonstrate that the relationships established within the short-wave region remain valid over a much broader frequency range. Furthermore, the model, now exclusively calibrated to BM data, predicts the behavior of the opposing side of the cochlear partition, aligning well with recent experimental observations. The success in reproducing key features of the experimental data and the mathematical simplicity of the resulting model provide strong support for the "overturned" theory of cochlear amplification.

Widely tunable magnetorheological metamaterials with nonlinear amplification mechanism

This paper proposes the design of an active nonlinear metamaterial for broadband and tunable low-frequency wave attenuation governed by a lever-based nonlinear amplification mechanism and a varying stiffness of a magnetorheological elastomer (MRE) driven by an external magnetic field. The metamaterial is formed by periodical spring-lever-MRE resonators connected to a base beam. Its strongly nonlinear behavior is described by a nonlinear amplification factor that depends on a magnetic flux density, a lever ratio, and an excitation amplitude. We use the Galerkin method to theoretically study the tunability of a low-frequency bandgap in terms of the MRE properties and the nonlinear amplification conditions. The obtained results are validated in numerical simulations. We also explore the mechanisms for broadband low-frequency wave attenuation governed by the strongly nonlinear dynamics of the proposed metabeam. Our results show that the metabeam with a large lever ratio can achieve substantial shifts of the bandgap frequencies for reasonably small variations of excitation amplitudes, while the bandgap size can be actively changed by varying the magnetic flux density. Our metamaterial is thus a promising solution to realize adaptive and actively tunable wave-attenuating metastructures that could be beneficial for practical applications.

Nonlinear Optical Pulses in Media with Asymmetric Gain.

A generic novel model governing optical pulse propagation in a nonlinear dispersive amplifying medium with asymmetric (linear spectral slope) gain is introduced. We examine the properties of asymmetric optical pulses formed in such gain-skewed media, both theoretically and numerically. We derive a dissipative optical modification of the classical shallow water equations that highlights an analogy between this phenomenon and hydrodynamic wave breaking. These findings provide insight into the nature of asymmetric optical pulses capable of accumulating large nonlinear phase without wave breaking, a crucial aspect in the design of nonlinear fiber amplifiers.

Deep neural network based downlink power domain multi-user NOMA-OFDM signal detection

Non-orthogonal multiple access-based orthogonal frequency division multiplexing (NOMA-OFDM) is a promising waveform-based multiple access technology for future wireless networks for multiple-user symbol transmission (MUST) in the same time-frequency resource block. However, it differs in the power domain, enhancing its spectrum efficiency. This is essential to meet the high data rate required for ever-increasing connected devices and the Internet of Things (IoT). However, NOMA-OFDM systems suffer from impairments such as imperfect successive interference cancellation (SIC) caused by channel impairments like channel fading, carrier frequency offset, and non-linearity caused by non-linear power amplifiers. This paper identifies and addresses the key impairments mentioned in the NOMA-OFDM system and proposes DNN-based estimation in offline training and detection in online testing for downlink power domain multi-user NOMA-OFDM symbols. The reported 2 dB SNR gain compared to least square-SIC/minimum mean square error SIC-based methods is a significant finding and demonstrates the robustness of the proposed DNN-aided approach against various channel impairments.

Semi-Supervised MIMO Detection Using Cycle-Consistent Generative Adversarial Network

In this paper, a new semi-supervised deep multiple-input multiple-output (MIMO) detection approach using a cycle-consistent generative adversarial network (CycleGAN) is proposed for communication systems without any prior knowledge of underlying channel distributions. Specifically, we propose the CycleGAN detector by constructing a bidirectional loop of two modified least squares generative adversarial networks (LS-GAN). The forward LS-GAN learns to model the transmission process, while the backward LS-GAN learns to detect the received signals. By optimizing the cycle-consistency of the transmitted and received signals through this loop, the proposed method is trained online and semi-supervisedly using both the pilots and the received payload data. As such, the demand on labelled training dataset is considerably controlled, and thus the overhead is effectively reduced. Numerical results show that the proposed CycleGAN detector achieves better performance in terms of both bit error-rate (BER) and achievable rate than existing semi-blind deep learning (DL) detection methods as well as conventional linear detectors, especially when considering signal distortion due to the nonlinearity of power amplifiers (PA) at the transmitter.

A Low-Complexity Digital Predistorter for Large-Scale MIMO Systems With Crosstalk

Massive multiple-input multiple-output (MIMO) technology is a key enabler for future wireless communication systems. On the other hand, crosstalk is inevitable in the highly integrated large-scale antenna array. The nonlinearity of power amplifiers (PAs) coupled with crosstalk is much more complicated when the number of antennas is large. Digital predistortion (DPD) can compensate for the PA nonlinearity without sacrificing efficiency and is widely applied in both base stations and mobile devices. Extending existing solutions to the large-scale MIMO system usually suffers from performance degradation or greatly increased complexity. In this paper, we consider the nonlinearity with crosstalk for the large-scale MIMO scenario. A much simplified DPD model is proposed by ignoring the high-order crosstalk terms generated from the complete nonlinear model. Compared to existing solutions, the proposed DPD can compensate for both the nonlinear and linear crosstalk of the system. It achieves satisfactory linearization performance with much reduced computational complexity. The complexity of the proposed DPD is linearly related to the number of transmitter branches. Thus, it is scalable in the large-scale MIMO scenario. Moreover, the proposed DPD can be extended to the partially-connected hybrid beamforming system with crosstalk. Simulation results validate the effectiveness of the proposed DPD scheme.

How well do hearing aids amplify “speech glimpses” in multitalker mixtures?

Reductions in speech audibility are more detrimental in the presence of competing sounds, where there is little redundant speech information, than in quiet. Indeed, our previous work suggests that insufficient audibility of “speech glimpses” may partly explain the poor performance of listeners with hearing loss in multitalker mixtures. An implication of those results is that restoring audibility across the spectrum may be especially critical in such situations. Here we asked whether current hearing-aid amplification strategies adequately restore the audibility of speech glimpses. We used ideal time-frequency separation to isolate target speech glimpses from unaided and aided speech mixtures. We then measured intelligibility for the isolated glimpses and for the original mixtures. Participants were young adults with bilateral sensorineural hearing loss, and individualized non-linear amplification (NAL-NL2) was provided using the Oldenburg open Master Hearing Aid. Results show that amplification generally improved the audibility and intelligibility of the target speech glimpses. For some participants, the intelligibility improvements carried over to the mixtures. For others, the improvements were diminished in the mixtures, suggesting that there were counteracting effects. This approach may provide a useful way to unpack positive and negative effects of hearing-aid processing in multitalker mixtures.

Improper Gaussian Signaling for IRS Assisted Multiuser SWIPT Systems With Hardware Impairments

In this paper, we focus on intelligent reflecting surface (IRS) assisted multiuser simultaneous wireless information and power transfer (SWIPT) systems with hardware impairments (HWIs), which result from the aggregate effect of in-phase and quadrature-phase imbalance (IQI), power amplifier non-linearity, quantization distortion, phase noise, etc. Improper Gaussian signaling (IGS) is employed to combat the signal distortion incurred by HWIs and the interference from other users. We aim to maximize the minimum achievable information rate among all users by jointly optimizing the active beamforming vectors, passive reflecting coefficients, and power splitting coefficients, subject to the minimum harvested energy requirements of these users and the total power budget at the transmitter. Due to the intricate coupling between the reflecting coefficients and beamforming vectors, we propose a two-level iterative optimization algorithm to solve this non-convex problem. Based on the above, we also study the weighted rate-energy region maximization problem. Numerical results show that the use of IGS significantly outperforms traditional proper Gaussian signaling (PGS) in the considered systems and also affirm the effectiveness of the proposed optimization algorithm.

Joint time domain nonlinear post-distortion scheme for reconstruction of distorted signals

Reconstruction of distorted signals (RODS), initially proposed in the frequency domain (FD), has been proved to be with high efficiency in depressing the distortion caused by the nonlinear power amplifier (PA). However, multiple high-dimensional transformation matrices are needed to reconstruct the FD distortion matrix, so high complexity is required. In this paper, we propose a new unified time domain (TD) nonlinear post-distortion scheme based on RODS, where a joint distortion matrix containing both PA and multipath channel coefficients is presented. When carrying out the least square inverse operation, the nonlinearity as well as channel fading effect can be eliminated simultaneously. By adjusting the elements in the distortion matrix according to the characteristics of PA and multipath channels, the proposed TD-RODS can also be suitable for flat fading with memoryless or memory nonlinear PAs. Further, the equivalence between the TD- and FD-RODS is presented, and then computer simulations are adopted to verify our analysis. In the proposed TD-RODS, the nonlinear distortion matrix is constructed more straightforward in a more cost-efficiency way, thus the overall computations is effectively reduced.

Computer model of the transponder for the analysis of phase distortions of the signal

The article discusses issues related to the development of a computer model of an on-board relay complex with linear signal retransmission for the analysis of phase distortion of the signal. It is very important to know the phase distortion (foray) when determining the coordinates of the radio source by the phase method using a virtual antenna array in satellite communication systems. The literature review given in the article showed that it was not possible to conduct these studies on existing computer models. Based on the classical version of the block diagram of the on-board relay complex, a computer model was developed in the MATLAB R 2016b (Simulink) environment. The model includes a receiving device, an input and output multiplexer and power amplifiers. Mathematical models of Saleh and Gorbanni amplifiers implemented on traveling wave lamps and solid-state amplifiers, respectively, were taken as nonlinear amplifiers. Multiplexers are implemented in the form of bandpass filters connected in parallel. The hybrid divider and ferrite circulators were not included in the model. In the model, it is possible to investigate the dependence of the phase distortion of the signal on the characteristics of the structural blocks of the on-board relay complex. The computer model also provides for the possibility of studying the effect of noise on phase distortion.