Pulse Dynamics Research Articles

Effect of shape and asymmetry of the voltage pulse on plasma sheath dynamics

In this paper, using particle-in-cell simulations and considering two symmetric voltage pulses with linear and exponential ramps, it is investigated how the voltage pulse shape affects the pulsed plasma sheath dynamics. Results show the formation, expansion, and shrinking of the sheath as well as the importance of the pulse shape in determining the sheath characteristics. The asymmetry effect of the pulse shape on the sheath evolution is also discussed. The ion kinetic energy and current density at the cathode surface are calculated. It is shown that the voltage change rate plays a significant role to determine the ion current density.

Experimental study of single-shot polarization dynamics of dual dissipative solitons

The state of polarization provides an additional dimension to the pulse dynamics of dissipative solitons. However, due to lack of appropriate measuring instruments, the polarization evolution of dual pulse vector solitons is still unclear. Here, for an erbium-doped fiber laser mode-locked with carbon nanotubes, we characterize the single-shot polarization evolution of dual dissipative solitons in detail using a high-speed wave-resolved measurement technique. For the different birefringence distributions in the laser cavity, the coupling between the orthogonal components of the vector soliton has a great influence on its physical properties, which may lead to various physical images of the vector soliton. We observed typical polarization-locked vector solitons and polarization attractors in the dual soliton pulses. We also observed that the polarization dynamics of the lead and tail vector pulses have similar evolution dynamics on the Poincaré sphere, while they have a distinct phase difference. By virtue of the difference of the processing SOPs between the leading and trailing pulses, we resolve three kinds of two solitons pulses with distinct relative phase evolutions. Our results enrich the vector soliton dynamics in fiber lasers.

Derivation new solitons and other solutions for higher order Sasa–Satsuma equation by using the improved modified extended tanh scheme

In this work, we utilize the improved modified extended tanh method to get optical solitons and other exact solutions for (3+1) dimensional Sasa–Satsuma model with third order dispersion that describe the dynamics of ultrashort pulses in the optical fibers. Many exact solutions are raised with the aid of the proposed method. These solutions include bright solitons, dark solitons, singular solitons, periodic wave solutions, hyperbolic wave solutions, Weierstrass elliptic solutions and Jacobi elliptic solutions.

Quantification of dissipative effects in a complex Ginzburg-Landau equation governed laser system by tracing soliton dynamics.

The concept of dissipative solitons has provided new insight into the complex pulse dynamics in mode-locked lasers and stimulated novel laser cavity designs. However, most of these studies are restricted to qualitative regimes, because it is difficult to quantify dissipative effects in a mode-locked laser. Meanwhile, the quantification of dissipative effects is a general problem that can be also encountered in other dissipative systems. In this paper, we demonstrate a method for quantifying dissipative effects in a mode-locked laser based on analyzing the soliton dynamics traced by time-stretch dispersive Fourier transform. As a result, we are able to quantitatively reproduce the evolution of the pulse that seeds mode-locking through simulations and gain a deeper understanding of the whole process. The obtained physical picture of mode-locking allows us to propose a simple method to quantify the energy threshold for mode-locking buildup and the stability of mode-locked states. A parameter is introduced to evaluate mode-locking conditions, which can serve as a criterion for designing mode-locked lasers. This work opens up new possibilities in the diagnosis and improvement of mode-locked lasers and studies of soliton physics.

Periodic and solitary waves generating in optical fiber amplifiers and fiber lasers with distributed parameters

We study self-similar dynamics of picosecond light pulses generating in optical fiber amplifiers and fiber lasers with distributed parameters. A rich variety of periodic and solitary wave solutions are derived for the governing generalized nonlinear Schrödinger equation with varying coefficients in the presence of gain effect. The constraint on distributed optical fiber parameters for the existence of these wave solutions is presented. The dynamical behaviour of those self-similar waves is discussed in a periodic distributed amplification system. The stability of periodic and solitary wave solutions is also studied numerically by adding white noise. It is proved by using the numerical split-step Fourier method that the profile of these nonlinear self-similar waves remains unchanged during evolution.

Generation and vector features of pulsating dissipative-soliton-resonance pulses in a figure-of-eight fiber laser

Pulsation, as one of the most distinctive nonlinear phenomena, exists in versatile fields. Pulsating solitons in dissipative optical systems have received considerable research interest due to their wealthy nonlinear dynamics and potential applications. Here, we demonstrate the generation of pulsating vector dissipative-soliton-resonance (DSR) pulses in an ytterbium-doped fiber laser based on a nonlinear amplifying loop mirror, for the first time. By decreasing the pump power, the stationary DSR pulse in the cavity could evolve into the pulsating DSR one, which undergoes periodic variations in its width and energy. In contrast to the conventional pulsating behavior with pulse peak power modulation, the pulsating DSR pulse maintains its peak power unchanged due to the strong peak-power-clamping effect. By utilizing a high-speed oscilloscope, the single-shot polarization-resolved temporal evolution of pulsating vector DSR pulses is monitored. By appropriately adjusting the net cavity birefringence through the intra-cavity polarization controllers, two types of pulsating vector DSR pulses, including the pulsating group-velocity-locked DSR (GVL-DSR) and pulsating polarization-locked DSR (PL-DSR) states, are achieved in the laser cavity. It is found that the two orthogonally polarized components have synchronized pulsating behaviors, but their central wavelengths can be the same or different. Our results would shed new light on the dynamics of DSR pulses.

Single-cavity dual-comb fiber lasers and their applications

Single-cavity, dual-comb lasers are those specially designed mode-locked lasers that can emit more than one, asynchronous ultrashort pulse trains with stable repetition frequency difference between them. Unlike the long-studied, widely-used femtosecond lasers generating one stable pulse train, systematic investigation on them and their potential dual-comb applications only began, based on the fiber laser platform, around a decade ago, despite sporadic and limited reports of similar lasing phenomena since the beginning of the mode-locked laser studies. From a historic perspective, the birth of this novel technology is the lucky outcome of the timely collision of perpetual search for novel pulsing laser dynamics and concerted pursuit of open-minded solutions for out-of-lab dual-comb systems in the 2010s. In this review article, first, the current schemes to implement single-cavity dual optical frequency comb fiber lasers and their applications are summarized, based on the concept of multiplexed mode-locked lasers. The characteristics of reported single-cavity, dual-comb fiber lasers are discussed as well as their applications in spectroscopy, ranging, Terahertz (THz) spectroscopy, and asynchronous optical sampling (ASOPS). Finally, the more recent development of single-cavity, multi-comb lasers is presented.

Dynamical system of optical soliton parameters by variational principle (super-Gaussian and super-sech pulses)

The parameter dynamics of super-sech and super-Gaussian pulses for the perturbed nonlinear Schrödinger’s equation with power-law nonlinearity is obtained in this article. The variational principle successfully recovers this dynamical system. The details of the variational principle with the implementation of the Euler–Lagrange’s equation to the nonlinear Schrödinger’s equation with power-law of nonlinearity described in this paper have not been previously reported.

Mathematical Model and Simulation of Blood Flow Dynamics in Renal Interlobar Artery of Patients with Human immunodeficiency Virus

Mathematical models were developed considering wall movement, blood pulsation and flow dynamics of the blood in the interlobar artery. The formulated models were based on the fact that the motion of blood vessel wall is not only influenced by pulsation, but also other physiological processes like heartbeat, breathing, and body posture. The Newton’s second Law of motion was employed in assembling the forces acting on the interlobar artery. The wall shear stress (WSS) was studied alongside, arterial walls to study the actual flow dynamics and investigate the blood flow behaviour. The results of the study were presented on both two – dimensional (2D) and three (3D) – dimensional graphs showing a more realistic interaction between the arterial wall and the blood flow in patients with HIV/AIDS. It was deduced that the blood flow velocity decreased with time across the varying frequency from 0.20Hz to 0.50Hz in the interlobar arterial channel.

Spectral pulsation dynamics of soliton molecules in ultrafast fiber lasers based on pump intensity modulation

<sec>This study employs real-time Fourier transform spectroscopy to investigate the pulsation dynamics of soliton molecules in a mode-locked erbium-doped fiber laser, by modulating pump intensity. By controlling the driving voltage of the pump source, we systematically observe and characterize the influence of external modulation signals on the amplitude, period, pulsation frequency, and the relative phase evolution among the pulsating soliton molecules in their spectra.</sec><sec>The results demonstrate that under specific conditions of pump intensity modulation, the pulsation period of soliton molecule spectra can be precisely regulated by the pump modulation frequency. At the same time, the amplitude of soliton molecule pulsations and the evolution of relative phase among the solitons are intricately tied to the pump modulation frequency. At lower modulation frequencies, such as 1 kHz, the relative phase among the pulses in the soliton molecule exhibits a sliding-type dynamics as a function of propagation time.</sec><sec>As the modulation frequency gradually increases to 5 kHz, a scenario emerges where three soliton molecules are generated. Notably, both the soliton spacing and relative phase undergo synchronous adjustments influenced by the pump modulation. With the modulation frequency further increasing, say, to 20 kHz, the relative phase evolution among the pulses within the soliton molecule gradually descends into chaos. This observation suggests the plausible existence of an inherent resonant frequency associated with pulsating soliton molecules, which has direct implications for their stability.</sec><sec>The findings of this research are of significance in advancing our comprehension of soliton molecule generation and enhancing their stability. In addition, they provide valuable insights into the broader domain of all-optical manipulation and applications of soliton molecules, and their application in pulse encoding in mode-locked laser systems.</sec>

Spectral pulsation dynamics of soliton molecules in ultrafast fiber lasers based on pump intensity modulation

This study employs real-time Fourier transform spectroscopy to investigate the pulsation dynamics of soliton molecules in a mode-locked erbium-doped fiber laser, utilizing pump intensity modulation. By manipulating the driving voltage of the pump source, we systematically observe and characterize the impact of external modulation signals on the amplitude, period, pulsation frequency, and the relative phase evolution among the pulsating soliton molecules within their spectra.The results demonstrate that, under specific conditions of pump intensity modulation, the pulsation period of soliton molecule spectra can be precisely regulated by the pump modulation frequency. Concurrently, the amplitude of soliton molecule pulsations and the evolution of relative phase among the solitons are intricately tied to the pump modulation frequency. At lower modulation frequencies, such as 1 kHz, the relative phase among the pulses within the soliton molecule exhibits a sliding-type dynamics as a function of propagation time.As the modulation frequency gradually increases, e.g., to 5 kHz, a scenario emerges where three soliton molecules are generated. Notably, both the soliton spacing and relative phase undergo synchronous adjustments influenced by the pump modulation. With further escalation of the modulation frequency, such as to 20 kHz, the relative phase evolution among the pulses within the soliton molecule gradually descends into chaos. This observation suggests the plausible existence of an inherent resonant frequency associated with pulsating soliton molecules, which has direct implications for their stability.The findings of this research hold significant relevance for advancing our comprehension of soliton molecule generation and enhancing their stability. Furthermore, they offer valuable insights into the broader domain of all-optical manipulation and applications of soliton molecules, as well as their utilization in pulse encoding within mode-locked laser systems.

Revealing the Evolution from Q-Switching to Mode-Locking in an Erbium-Doped Fiber Laser Using Tungsten Trioxide Saturable Absorber

Passively Q-switching and mode-locking technologies can generate short pulses with durations that differ by several orders of magnitude widely used in different applications. Recently, Q-switching and mode-locking realized in an identical laser cavity with saturable absorbers was reported. The analysis of pulse conversion is helpful for us to further understand the pulse dynamics of a laser. In this paper, the pulse evolution from Q-switching, Q-switched mode-locking to mode-locking, is demonstrated by using a tungsten trioxide saturable absorber in a ring-cavity erbium-doped fiber laser. Firstly, self-started Q-switching at 1563 nm is observed, the repetition rate continuously increases, and the duration decreases when the pump power increased. Then, with an adjusting intra-cavity state of polarization under a high pump power level, stable Q-switched mode-locking pulses evolved from Q-switching, are observed. The amplitude of the emerged pulse sequence with a period of 36.8 ns, determined by cavity length, is modulated by the Q-switched envelope with the period of 10.3 μs. By optimizing the intracavity polarization carefully, stable continuous wave mode-locking operation is achieved eventually. To the best of our knowledge, this is the first experimental demonstration of Q-switching and mode-locking, respectively, in an identical transition-metal-oxides-based pulsed fiber laser without modification of cavity structure.

Fast and slow optical rogue waves in the fiber laser

We reported an experimental study on fast and slow temporal scaling of rogue waves’ emergence in a long (615 m) ring cavity erbium-doped fiber laser. The criterion for distinguishing between the fast and slow rogue waves is a comparison of the event lifetime with the system’s main characteristic time estimated from the decay of an autocorrelation function (AF). Thus, compared with the AF characteristic time, fast optical rogue wave (FORW) events have lifetime duration shorter than the AF decay time, and they appeared due to the mechanism of the pulse-to-pulse interaction and nonlinear pulse dynamics. In contrast, a slow optical rogue wave (SORW) has lifetime duration much longer than the decay time of the AF, which results from the hopping between different attractors. Switching between regimes can be managed by adjusting the in-cavity birefringence.

Solitons solutions to the high-order dispersive cubic–quintic Schrödinger equation in optical fibers

In this paper, solitons solutions of higher-order dispersive cubic–quintic Schrödinger equationincluding third-order as well as fourth-order derivatives with respect to time, that describes the dynamics of ultrashort pulses in optical fibers are investigated in detail. In this respect,a solution procedure in the locality of applied mathematics called the hyperbolic function method is appliedusing multi-linear variable separation approach (MLVSA). As an outcome, a bunch of soliton solutions isderived in conjunction with plotting dark and periodic wave solutions. The credibility of the results is examined by setting each solution back into its governing equation. Through portraits, different forms of wave solutions are depicted. Moreover, the restrictions on the parameters are also given for the existence of the obtained solutions.

Acoustic solitons in a periodic waveguide: Theory and experiments

We study the propagation of high-amplitude sound waves, in the form of pulse-like solitary waves, in an air-filled acoustic waveguide of periodically varying cross section. Our numerical simulations, solving the compressible Navier–Stokes equations in two dimensions, as well as our experimental results, strongly suggest that nonlinear losses, originated from vortex shedding (at the segment changes) are crucial in the dynamics of high amplitude pulses. We find that, even in the presence of strong dissipation, the solitary wave roughly retains its characteristics (as described by the amplitude–velocity–width relations), obtained by the derivation and analysis of an effective Boussinesq equation. In addition, we propose a transmission-line based numerical scheme, able to capture well the experimental results. The proposed design offers a new playground for the study of the combined effects of dispersion, nonlinearity and dissipation in air-borne acoustics, while, due to its simplicity, it can be extended to higher dimensions.

Investigations on pulse dynamics and offset spectral filtering in Er-doped Mamyshev fiber oscillator

We have experimentally established an all fiber Er-doped Mamyshev oscillator that is self-started with an external seed laser. The Mamyshev fiber oscillator emitted pulses with a repetition rate of 6.54 MHz and pulse duration of 1.61 ps. Both the buildup dynamics and intracavity evolution dynamics are numerically modeledwith nonlinear Schrödinger equation. The impact of offset spectral filtering including frequency offset and spectrum bandwidth on the Mamyshev fiber oscillator is simulated. Numerical results show that these parameters can influence the physical properties of output pulses in Mamyshev oscillator, which is analogous to the saturable absorber. These findings provide a deep understanding of the significance of offset spectrum filtering in Er-doped Mamyshev fiber oscillators, as well as a foundation for the design of fiber lasers in practical applications.

Nanosecond pulsed discharge dynamics during passage of a transient laminar flame

This work presents an experimental study of a nanosecond repetitively pulsed dielectric barrier discharge interacting with a transient laminar flame propagating in a channel of height near the quenching distance of the flame. The discharge and the flame are of comparable size, and the discharge is favoured at a location where it is coupled with the reaction zone and burnt gas. The primary goal is to determine how the discharge evolves on the time scale of the flame passage, with the evolution driven by the changing gas state produced by the moving flame front. This work complements the large body of work investigating the effect of plasma to modify flame dynamics, by considering the other side of the interaction (how the discharge is modified by the flame). The hot gas produced by the combustion had a strong effect on the discharge, with the discharge preferentially forming in the region of hot combustion products. The per-pulse energy deposited by the discharge was measured and found to increase with the size of the discharge region and applied voltage. The pulse repetition frequency did not have a direct impact on the per-pulse energy, but did have an effect on the morphology and size of the discharge region. Two distinct discharge regimes were observed: uniform and filamentary (microdischarges). Higher pulse repetition frequencies and faster-cooling combustion products were more likely to transition to the filamentary regime, while lower frequencies and slower-cooling combustion products maintained a uniform regime for the entirety of the time the discharge was active. This regime transition was influenced by the ratio of the time scale of fluid motion to the pulse repetition rate (with no noticeable impact caused by the reduced electric field), with the filamentary regime preferentially observed in situations where this ratio was small. This work demonstrates the importance of considering how the discharge properties will change due to combustion processes in applications utilizing plasma assistance for transient combustion systems.

Interaction between double solitons in anti-PT symmetric synthetic photonic lattices

An anti-parity-time symmetry (anti-PT symmetric) double fiber loop synthetic photonic lattice is constructed theoretically by projecting the intensity of two loops and adjusting the phase and gain/loss distribution. Numerical studies on pulse dynamics show that the trajectories of double-pulse solitons may be manipulated by tuning the initial relative phases, pulse separation, nonlinearity, and non-Hermitian characteristics of the system. Our research may provide a new way to realize logic gate devices and optical switches in optical interconnection and optical communications.

Two-Layered Microfluidic Devices for High-Throughput Dynamic Analysis of Synthetic Gene Circuits in E. coli.

Escherichia coli is a common chassis for synthetic gene circuit studies. In addition to the dose-response of synthetic gene circuits, the analysis of dynamic responses is also an important part of the future design of more complicated synthetic systems. Recently, microfluidic-based methods have been widely used for the analysis of gene expression dynamics. Here, we established a two-layered microfluidic platform for the systematic characterization of synthetic gene circuits (eight strains in eight different culture environments could be observed simultaneously with a 5 min time resolution). With this platform, both dose responses and dynamic responses with a high temporal resolution could be easily derived for further analysis. A controlled environment ensures the stability of the bacterial growth rate, excluding changes in gene expression dynamics caused by changes of the growth dilution rate. The precise environmental switch and automatic micrograph shooting ensured that there was nearly no time lag between the inducer addition and the data recording. We studied four four-node incoherent-feedforward-loop (IFFL) networks with different operators using this device. The experimental results showed that as the effect of inhibition increased, two of the IFFL networks generated pulselike dynamic gene expressions in the range of the inducer concentrations, which was different from the dynamics of the two other circuits with only a simple pattern of rising to the platform. Through fitting the dose-response curves and the dynamic response curves, corresponding parameters were derived and introduced to a simple model that could qualitatively explain the generation of pulse dynamics.

Thermal effects in short laser pulses: Suppression of wave collapse

An envelope model for short laser pulses is proposed. These pulses are short compared to fluid motion timescales and long compared to electron thermalization timescales. Numerical simulation of the thermal blooming of laser pulses at powers near the boundary of the self-focusing regime is presented in this model. The model includes terms representing the contributions of thermal blooming and the Kerr effect. In the context of the model, thermal blooming and the Kerr effect compete; Kerr driving and thermal blooming suppressing wave collapse. The dynamics of pulses whose energies are near the collapse threshold are numerically simulated.