Pulse Dynamics Research Articles

Dynamics of optical pulses with the effect of second-order spatiotemporal dispersion

Dynamics of optical pulses with the effect of second-order spatiotemporal dispersion

Pair induced quenching in high concentration Holmium-doped fiber amplifiers

The spectrum required for future optical communication systems is being extended towards the C-, L- and U-bands, resulting in a significant interest in the spectral region around 2 μm wavelength. Since Holmium doped fiber amplifiers (HDFAs) provide amplification in this spectral region, they have become a focus of researchers working on doped fiber amplifiers. A major factor resulting in the performance degradation of HDFAs is the inhomogeneous energy transfer within Ho3+ ion-pairs in high-concentration Holmium-doped fibers (HDFs), an effect generally known as pair-induced quenching (PIQ). In this paper, we study the luminal and temporal dynamics of pulses of different repetition rates at 2.05 μm in high-concentration HDFs considering the effects of ion-pairs. Input pulses having repetition rates of 25 GHz and 500 kHz are generated using wavelength tunable actively mode-locked Holmium-doped fiber laser (AML-HDFL) based on a single ring cavity and bidirectional pumping. The characteristics of the pulses propagating through high-concentration HDF are analyzed based on different metrics such as average power, peak power, pulse energy, full-width at half maximum (FWHM), and time delay without and with ion-pairs for values of fraction of ion-pairs k = 0 and k = 10%, respectively. The results obtained at optimized length of HDF show that ion-pairs significantly degrade the average power, peak power, and energy of the output pulses for both of the repetition rates. For both k = 0 and k = 10%, the FWHM and shape of the output pulses remain same in the presence of the ion-pairs while, time delay of 4 ps and 19 ns is observed in the output pulses at repetition rates of 25 GHz and 500 kHz, respectively. The effects of increasing the pump and signal power on the average power and energy of the output pulses for k = 0 and k = 10% are also discussed for both repetition rates. This analysis provides important guidelines for designers of 2 μm fiber lasers and amplifiers based on high-concentration HDFs.

THz generation and spatiotemporal variation of two cross‐focused Gaussian laser pulses in plasma

AbstractThe impact of spatial and temporal evolution of nonlinear mixing of two Gaussian laser pulses propagating in plasma on generation of terahertz (THz) radiation have been investigated taking into account the ponderomotive nonlinearity. By calculating the modified electron density of plasma caused by the finite ponderomotive force of the pump lasers and using wave equation and paraxial ray approximation, two coupled governing equations for temporal and spatial pulse‐width parameters have been derived. The electric field of the THz wave as a result of nonlinear current density induced by the beat ponderomotive force of the pulses was extracted. Combined effects of initial laser and plasma parameters on the behavior of self‐compression and self‐focusing as well as THz radiation generation were investigated. The numerical results indicated a considerable spatiotemporal compression takes place within a specific range of laser intensity, exhibiting a saturation intensity point where the compression process reaches its maximum extent. It is observed that the generated THz radiation also strongly depends on the spatiotemporal dynamics of the pump pulses. The maximum THz amplitude corresponds to the strongest pump pulse compression extent.

Harnessing ultrawideband technology for enhanced communication and radar detection

This article explores the field of pulse dynamics in functional materials with an emphasis on their use in ultrawideband technology and its significance in high-frequency situations. For thirty years, a great deal of attention in the scientific and technical literature has focused on the production of high-power Gaussian pulses, which are necessary to improve radar detection capabilities. Most notably, using avalanche transistors in conjunction with Step Recovery Diodes has been shown to be an effective way to build pulse generators that support narrow pulse widths. Also describes the complex transistor-based circuitry used to generate pulses, which is based on the avalanche mode principle and requires careful pulse shaping. The balun device is a key component of this technology since it optimizes signal integrity by converting asymmetrical pulses into balanced ones. Step Recovery Diodes are also essential for fine-tuning pulse edges, which guarantees accurate temporal properties that improve communication efficiency. This article offers insights into the transformational potential of UWB technology by offering a thorough review of the technology, including prospective applications and regulatory implications. UWB technology is ready to completely transform the field, from making old communication paradigms obsolete to bringing in a new era of unheard-of communication capabilities. All things considered, this work advances our understanding of UWB technology and pulse dynamics in a sophisticated way, making it an invaluable tool for engineers, researchers, and legislators.

Airy pulse dynamics in semiconductor optical amplifier with dispersive gain

We analytically as well as numerically study the Airy pulse dynamics in semiconductor optical amplifier (SOA) with dispersive gain. The frequency dependent gain of the SOA not only modifies the temporal shape of the Airy pulse but also alters the peak power of the Airy pulse. The study finds that the trajectory of the Airy pulse can be manipulated by the gain induced dispersion and the linewidth enhancement factor. Moreover, the gain dispersion introduces upchirp during the propagation that suppresses the Airy pulse acceleration in anomalous group velocity dispersion while the acceleration is pronounced when the dispersion is normal.

Pulsed interactions unify reaction–diffusion and spatial nonlocal models for biological pattern formation

The emergence of a spatially organized population distribution depends on the dynamics of the population and mediators of interaction (activators and inhibitors). Two broad classes of models have been used to investigate when and how self-organization is triggered, namely reaction–diffusion and spatially nonlocal models. Nevertheless, these models implicitly assume smooth propagation scenarios, neglecting that individuals interact many times by exchanging short and abrupt pulses of the mediating substance. A recently proposed framework has made advances in properly accounting for these short-scale fluctuations by applying a coarse-graining procedure on the pulse dynamics. In this paper, we generalize the coarse-graining procedure and apply the extended formalism to new scenarios in which mediators influence individuals’ reproductive success or their motility. We show that, in the slow- and fast-mediator limits, pulsed interactions recover, respectively, the reaction–diffusion and nonlocal models, providing a mechanistic connection between them. Furthermore, at each limit, the spatial stability condition is qualitatively different, leading to a timescale-induced transition where spatial patterns emerge as mediator dynamics becomes sufficiently fast.

The periodic soliton solutions for a nonlocal nonlinear Schrödinger equation with higher-order dispersion

A nonlocal nonlinear Schr¨odinger (NNLS) equation with fourth-order dispersion and cubic-quintic nonlinearities has been studied analytically and numeri- cally. Under the constraint conditions, auxiliary functions are introduced, and explicit one- and two-soliton solutions are obtained by the Hirota bilinear method. Accord- ing to the solutions, the propagation dynamics of soliton pulses are investigated. The influences of different parameters on the dynamics of one- and two-soliton solutions have been analyzed. The results show that the two-soliton solution exhibits diverse dy- namic characteristics under the suitable parameter selections. In addition, the stability of one- and two-soliton solutions against the constraint conditions deviations and under the initial perturbations are also studied numerically.

Sub-gigahertz bandwidth all-optical tunable differentiator with high-energy efficiency based on a micro-ring resonator.

We propose and demonstrate a tunable fractional-order photonic differentiator (DIFF) that can process input pulses with a sub-gigahertz bandwidth. Our scheme utilizes the self-induced optical modulation effect observed in a silicon-on-insulator micro-ring resonator. Gaussian-like pulses with varying pulse widths between 7.5 and 20 ns are employed for differentiation, achieving an energy efficiency over 45%, to the best of our knowledge, which surpasses all previously reported schemes for input pulses with a sub-gigahertz bandwidth. We simulate the temporal dynamics of pulses to gain insight into the physical mechanisms underlying the differentiated outputs and provide a method for differentiation order adjustment, which is experimentally realized using an all-optical pump-probe technique.

Chirped self-similar optical solitons with cubic–quintic–septic–nonic form of self-phase modulation

This study investigates the dynamics of ultrashort light pulses in an inhomogeneous optical medium exhibiting all orders of nonlinearity up to the ninth order. The research focuses on exploring the existence and properties of self-similar solitons while varying cubic, quintic, septic, and nonic nonlinearities, group velocity dispersion, and loss or gain. It is found that the transmission system supports the existence of novel types of self-similar bright and dark pulses in the presence of various physical processes. Importantly, these self-similar localized waves exhibit a linear chirp, a crucial factor for achieving effective pulse amplification or compression. Based on the chirp property, the dynamical behaviors of these self-similar waveforms are discussed in a periodically distributed amplification system. The findings highlight that the shape and dynamics of these chirped self-similar pulses can be precisely controlled by selecting appropriate profiles for gain or loss, nonlinearity, and dispersion. Additionally, the research numerically discusses the interaction dynamics between two and three adjacent solitons.

Generation and observation of noise-like pulses in an ultrafast fiber laser at 1.7 μm

In this manuscript, we demonstrate the generation and real-time dynamics of noise-like pulses (NLPs) in a 1.7 μm ultrafast thulium-doped fiber laser with all-fiber structure. NLPs with a central wavelength of ∼ 1742.5 nm and a 3-dB spectral width of ∼ 10.95 nm could be observed with pulse energy up to 4.19 nJ. The dynamic characteristics of NLPs were explored by using time-stretch dispersive Fourier transformation technology, which shows that the NLPs actually consist of many chaotic small pulse envelopes with random and changeable energies. These experimental results indicate that NLPs are the intrinsic features of fiber lasers and hold significant importance for further academic research, which can contribute to the development and application of 1.7 μm fiber laser in fields such as biomedicine and short-range remote sensing.

Pulse buildup dynamics in a self-starting Mamyshev oscillator.

The Mamyshev oscillator (MO) can generate high-performance pulses. However, due to their non-resonant cavities, they usually are not self-starting, and there is almost no effort to reveal the pulse buildup dynamics of the MO. This paper investigates the dynamic of single pulse (SP) and multi-pulse formation in a self-starting MO. It indicated that both SP self-starting and multi-pulse self-starting can be obtained by adjusting the oscillator parameters. More importantly, increasing pump power could only result in bound state pulses (BSPs) if SP self-starting was formed. With the increase of the pump power, the pulse number in BSPs would increase. However, multiple pulses could not be formed only by increasing the pump power, and the BSPs obtained here underwent SP generated from noise, amplified, and then bounded, which is different from conventional passive mode-locked fiber lasers (CPMLFLs). On the other hand, if multiple pulses were self-initiated, BSPs, pulse bunch, and harmonic mode-locked pulses (HMLPs) could be obtained by adjusting the polarization state and pump power in the cavity. Furthermore, once any of the above states are formed, if the oscillator polarization state and filter interval are unchanged, only increasing the pump power from zero, the original state can still be obtained, which is consistent with the characteristics of the CPMLFLs. These findings will provide new insights into the pulse dynamics of self-starting MO, which will be significant for studying ultrafast laser technology and nonlinear optics.

Enhanced bi-LSTM for Modeling Nonlinear Amplification Dynamics of Ultra-Short Optical Pulses

Enhanced bi-LSTM for Modeling Nonlinear Amplification Dynamics of Ultra-Short Optical Pulses

Generation and Dynamics of Multiple Pulses in an Ultrafast Fiber Laser with a Single-Mode Fiber–Graded-Index Multimode Fiber–Single-Mode Fiber-Based Saturable Absorber

In this study, we have investigated the evolution process and dynamic characteristics of a multi-pulse regime in an erbium-doped fiber ring laser based on a single-mode fiber–graded-index multimode fiber–single-mode fiber (SMF-GIMF-SMF) structure as an optical modulator. By utilizing the excellent nonlinear optical absorption of the SMF-GIMF-SMF (SMS) device with a modulation depth of ~8.68%, stable single-pulse mode locking at the frequency of 9.84 MHz can be readily observed at low pump power. In addition, the single-pulse operation can evolve into a multiple-pulse regime on account of the peak-power-clamping effect via suitably raising the pump power and carefully regulating the polarization state. Further, the single-shot temporal evolution of multiple pulses is monitored, indicating that this state shows unique and interesting temporal characteristics with variable pulse separations and inconsistent pulse intensities, which, as far as we know, is the first such observation in ultrafast fiber lasers. Additionally, this study, based on the time-stretch dispersive Fourier transformation method, suggests that these multiple pulses consist of chaotic wave envelopes with erratic intensities and changeable pulse energy. We believe that these findings have profound implications for revealing fascinating nonlinear pulse dynamics in ultrafast fiber optics.

Effect of Stimulated Raman Self-Scattering on the Dynamics of Pulses in a Gradient Waveguide

Effect of Stimulated Raman Self-Scattering on the Dynamics of Pulses in a Gradient Waveguide

Progressive pulse dynamics in a mode-locked fiber laser

Progressive pulse dynamics in a mode-locked fiber laser

Efficient Physics-informed Neural Network for Ultrashort Pulse Dynamics in Optical Fibers

Efficient Physics-informed Neural Network for Ultrashort Pulse Dynamics in Optical Fibers

Linear filtration waves in a layered heterogeneous formation

Solutions to the problem of a filtration-wave pressure field in a layered inhomogeneous medium with a pressure pulse specified on the left boundary are obtained. The problem statement contains a two-dimensional wave equation in the central layer, a wave equation that takes into account the predominance of vertical motion in the environment, symmetry conditions in the center of the formation, equality of pressures and flows at the interfaces, the absence of disturbances of the filtration wave field at the initial moment of time and at an infinite distance from the source of disturbance. The article found an exact solution to the problem obtained using the Laplace–Carson and the Fourier transform of sine, an asymptotic solution and an exact solution for the special case of a homogeneous medium. It is shown that when the formal parameter tends to zero, the exact solution coincides with the main asymptotic approximation. The tendency of the thickness of the central layer to infinity reduces the solution for a layered inhomogeneous medium to an expression describing the pressure fields in a homogeneous medium. Spatiotemporal dependencies describing the dynamics of the pressure pulse in layered inhomogeneous and homogeneous media were constructed, and the general properties and features of linear filtration waves in layered inhomogeneous and homogeneous layers were studied.

Narrow-bandwidth picosecond dissipative soliton resonance in an all-anomalous-dispersion Er/Yb co-doped fiber laser

First, it is numerically demonstrated that narrow-bandwidth picosecond dissipative soliton resonance (DSR) pulses can be obtained in the all-anomalous-dispersion Er/Yb co-doped fiber (EYDF) laser, which is based on the nonlinear polarization rotation (NPR) mode-locking and narrow-band spectral filtering. The generated DSR pulses are characterized by a central peak on top of a rectangular pedestal temporally and two high-intensity spectral sidebands with less than 0.6-nm bandwidth. Second, the impacts of several key cavity parameters on characteristics of DSR pulses are investigated. Particularly, a new phenomenon of periodic evolution of the DSR pulse, featuring alternated high and low peak powers with the round-trips, is discovered by tuning filter bandwidth or net-cavity dispersion. Multi-pulse dissipative soliton (DS) and noise-like pulse (NLP) are also observed in the fiber laser. Finally, a 22.3-ps DSR pulse with 287.5-W peak power can be further compressed to 4.3 ps with 1126.5-W peak power by the dispersion compensation. This work further enriches the DSR pulse dynamics in the anomalous-dispersion region and paves a way to realize narrow-bandwidth picosecond DSR pulse fiber lasers.

Peculiarities of Pulse Dynamics in Stratified Incompressible Media

Peculiarities of Pulse Dynamics in Stratified Incompressible Media

Dynamics of pulsational mode in the EiBI gravity fabric

We systematically theorise a model formalism to investigate the linear pulsational mode dynamics excitable in self-gravitating dust molecular clouds (DMCs) in the framework of the Eddington-inspired Born-Infeld (EiBI) gravity. The adopted spherical DMC consists of thermalized lighter (non-inertial) electrons and ions, both treated analogously as the Boltzmann species, whereas the partially ionised heavier (inertial) dust grains as the constitutive neutral and charged dust fluids. The model closure comes from the coupling gravito-electrostatic Poisson equations governing the resultant potential distributions sourced in the material and charge density fields. Application of spherical normal mode (Fourier-based) analysis transforms the model DMC into a quartic linear dispersion relation with diverse atypical multi-parametric dispersion coefficients. A numerical platform is constructed for an illustrative dispersion analysis. It shows that the positive EiBI parameter, dust charge number, and cloud size act as stabilizing agents against the inward non-local self-gravity. In contrast, a negative EiBI parameter, dust mass, and equilibrium dust population density play destabilizing roles. The modal propagatory and oscillatory features are portrayed graphically and interpreted elaborately. The reliability of our calculation scheme is validated in light of the closely related results previously reported in the literature. The analyses presented here could be relevant in the context of understanding astrophysical structure formation dynamics through the self-gravitational canonical condensation processes in diverse real astronomic environs.