Multi Pulses Research Articles

Dynamic characteristics and conversion process of solitons in a Mamyshev oscillator

The Mamyshev oscillator (MO) can produce not only a single pulse (SP) but also multi-pulses (MPs). However, most of the research focuses on increasing the output pulse energy and reducing the pulse width, and only some studies reveal the characteristics of MPs output. More research is needed on achieving the conversion from MPs to SP by adjusting the oscillator parameters and determining what intermediate states will be experienced in the conversion process. Here, we study the dynamic characteristics of soliton and the conversion process between different output states of ultrafast MO. By adjusting the gain saturation energy and filter interval, we obtain the relationship between the number of MPs outputs and the oscillator parameters and observe the intermediate process from MPs pulsation to SP. The research results reveal the dynamic characteristics of non-equilibrium optical solitons, assisting in optimizing MO design.

Functional integration of handwritten digit recognition and encryption/decryption based on Pt/GaOx/TiN memristor array for a new data security system

In the age of big data, information security has become more and more essential for the Internet of Things. Since the software encryption algorithm can be easily hacked, the hardware security system has emerged as a reliable way to safeguard information. Here, a GaOx-based memristor array is experimentally demonstrated, which features a good multi-level storage capacity, 20 ns switching speed, and highly linear conductance modulation of over 500 states by multi pulses. An artificial neural network and an XOR circuit were further constructed based on this memristor array. This work connects memristor array-based handwritten digit recognition and data security circuit, forming a new data security management system for secure password input and transmission.

Ni-Silicide Ohmic Contacts on 4H-SiC Formed by Multi Pulse Excimer Laser Annealing

The formation of ohmic contacts by laser annealing approach is of great importance for SiC power devices, since it allows their fabrication on thin substrates, that is of crucial significance to reduce power dissipation. Ni silicide reaction under UV laser irradiation has been studied in detail with particular focus on single pulse approach, in order to describe the early stage of reaction process. The use of a multi pulse approach, for the formation of Ni silicide-based ohmic contacts by means of excimer laser annealing, has been investigated in this work. The reaction process has been characterized, as a function of number of pulses, by means of X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) analysis. Laser process simulations, formulated in the framework of phase field theory, have been performed in order to predict the evolution of material during reaction under annealing. Simulations show that reaction moves to Si-reach phases with the increasing on pulses, with a co-existence of Ni2Si and Ni3Si2 phases for the three pulses process. Moreover, simulations show critical differences, in terms of the uniformity of the distribution of the silicide phases along the film, between the single pulse and the multi pulses cases and the increasing of thickness of silicide phases with the pulse sequence. These predictions are in good agreement with the findings of XRD and TEM analyses. The electrical properties of the reacted layer have been evaluated on Schottky Barrier Diodes (SBD) devices, confirming the ohmic behaviour of multi pulse annealed samples.

An in-depth investigation into high fluence femtosecond laser percussion drilling of titanium alloy

High fluence femtosecond laser percussion drilling has a potential to produce micro holes for cooling purpose in turbine blades made of titanium alloys due to its short interaction time with the material. For an in-depth investigation, numerical simulation is carried out using 2D axi-symmetric two-temperature and heat conduction models in tandem, mimicking the laser percussion drilling. Moving mesh approach in finite element based COMSOL Multiphysics software is used to arrive at the crater geometry during the ablation process. The heat conduction model provides the value of surface temperature after each pulse. Taking temperature-dependent thermo-physical and optical properties with intraband absorption effect, the simulations are carried out on a 2 mm thick Ti6Al4V plate for 1–15 pulses with fluence in the range of 0.84 to 8.4 J cm−2. For comparison, the simulation results based on room temperature properties are also included. Validation experiments are carried out and the crater morphology is measured using laser scanning confocal microscope. The overall average absolute deviations of the results for crater diameter and depth are within 20% and 40% respectively. The proposed simulation approach is robust and can be used to investigate multi pulses laser ablation process in any other applications.

Femtosecond laser ablation and photo-induced effects of As40S60, Ga08As392S60 and Ga08As292Sb10S60 chalcogenide glasses

Laser induced damage thresholds (LIDTs) and photo-induced changes of As40S60, Ga0.8As39.2S60 and Ga0.8As29.2Sb10S60 chalcogenide glasses are investigated by femtosecond laser of 800 nm. As40S60 glass has the highest LIDT as well as 1452.3 mJ/cm2, the introduction of small amount of Ga and Sb into glass decreases the LIDTs to 957.1 mJ/cm2 for Ga0.8As39.2S60 and 705.9 mJ/cm2 for Ga0.8As29.2Sb10S60, respectively. Microstructure analysis reveals that the decrease of LIDT is tightly related to the decrease of high strength chemical bonds and formation of lower ones in glass matrix. After multi pulses induced damage occurred, the structure of glass matrix became more random and a half of S was replaced by O approximately. The damage mechanism was proposed and it is helpful to develop high LIDT chalcogenide glasses and the photo-induced effects are the basis of waveguide writing in chalcogenide glasses by femtosecond laser.

Stability and interaction of few-cycle pulses in a Kerr medium.

The different aspects of few-cycle pulse dynamics governed by the regularized short pulse equation (RSPE) are reported. It is shown that the RSPE provides an accurate description of the dynamics of the few-cycle pulse whose duration is larger than a single optical period when the few-cycle pulse's spectrum is in the medium's anomalous dispersion regime. The approximate solutions of the RSPE are constructed from the soliton solutions of the nonlinear Schrödinger (NLS) equation. We demonstrate numerically that the stability of these few-cycle pulses strongly depends on their pulse duration. Furthermore, the interactions of the two and three few-cycle pulses are studied. When pulse parameters are suitably chosen, we show the elastic collision, inelastic collision and repulsive interaction between these multi few-cycle pulses. It is revealed that the interactions of the multi few-cycle pulses rely heavily on their pulse duration.

Investigations on femtosecond laser modified micro-textured surface with anti-friction property on bearing steel GCr15

This work puts forward femtosecond laser modification of micro-textured surface on bearing steel GCr15 in order to reduce frictional wear and enhance load capacity during its application. Multi pulses femtosecond laser ablation experiments are established for the confirmation of laser spot radius as well as single pulse threshold fluence and pulse incubation coefficient of bulk material. Analytical models are set up in combination with hydrodynamics lubrication theory. Corresponding simulations are carried out on to explore influences of surface and cross sectional morphology of textures on hydrodynamics lubrication effect based on Navier-Stokes (N-S) equation. Technological experiments focus on the impacts of femtosecond laser machining variables, like scanning times, scanning velocity, pulse frequency and scanning gap on morphology of grooves as well as realization of optimized textures proposed by simulations, mechanisms of which are analyzed from multiple perspectives. Results of unidirectional rotating friction tests suggest that spherical texture with depth-to-width ratio of 0.2 can significantly improve tribological properties at low loading and velocity condition comparing with un-textured and other textured surfaces, which also verifies the accuracy of simulations and feasibility of femtosecond laser in modification of micro-textured surface.

TEMPORAL SOLITON: GENERATION AND APPLICATIONS IN OPTICAL COMMUNICATIONS

In general, the temporal and spectral shape of a short optical soliton pulse does not change during propagation in a nonlinear medium due to the Kerr effect which balances the chromatic dispersion. Microring resonators (MRRs) can be used to generate chaotic signals. The smaller MRR is used to form the stopping and filtering system. The employed optical material was InGaAsP/InP, which is suitable for use in the practical devices and systems. The tuning and manipulation of the bandwidth of the soliton signals is recommended to control the output signals. The MRRs can be applied to produce ultra-short pulses, where the medium has a nonlinear condition, thus, using of soliton laser becomes an interesting subject. Therefore, an ultra-short pulse in the scope of pico and femtoseconds soliton pulses can be utilized for many applications in engineering communications. In order to obtain smaller bandwidth of the optical soliton pulses, we propose integrating series of MRRs. In this study, 5 fs soliton pulse could be generated using a series of five MRRs. The soliton signals experience less loss during the propagation, where they are more stable compared to normal conventional laser pulses. Using the series of MRRs connected to an add/drop system, shorter soliton bandwidth and highly multi soliton pulses can be obtained. Therefore, generation of ultra-short multi picosecond (1.2 and 1.3 ps), could be performed, where the radius of the add/drop system has been selected to 50 and 300 µm respectively.

Optical Quantum Generation and Transmission of 57–61 GHz Frequency Band Using an Optical Fiber Optics

An optical panda ring resonator connecting to two microring resonators (MRRs) can be used to generate a high frequency optical soliton. The optical soliton pulse of 57-61 GHz can be generated and transmitted via an optical quantum transmission link. This system uses a Gaussian laser pulse propagating within a nonlinear MRRs system. The ultra-short single and multi soliton pulses within the range of 57-61 GHz can be generated and seen at the through and drop ports of the system. The transmission link consists of MRRs system, optical transmitter, connector, fiber optics, erbium doped fiber amplifier (EDFA), receiver and antenna which provide transmission of optical soliton via the wired/wireless communications. The fiber optic has a length of 1 km, where the wireless link covers a short distance optical communication of 10 m. Here, the transmitted optical soliton pulses can be received, detected and used by the users.

Методы широтно-импульсной модуляции мощных активных выпрямителей при несимметрии напряжения

Powerful main electric drive rolling mills are made, usually multi pulses using synchronous motor and frequency converters, consisting of active rectifier and autonomous voltage inverter. Such schemes allow the use of PWM techniques that provide low frequency switching power switches acceptable harmonic structure of the network current transformers and voltage at the point of common coupling. This is due to the property of three-phase systems, ensuring the absence of harmonic multiples of three. These properties are valid only if the symmetry of voltage, so unbalanced currents appear in all odd harmonic spectrum and the application of a low switching frequency becomes invalid. The article presents the results of a study on the mathematical model of the main drive of a cold rolling mill 2000 different methods of PWM in balanced and unbalanced modes. Methods PWM five switchings per quarter period (removing 11, 13, 23, 25 harmonics), with nine switching quarter period (removing 3, 5, 7, 9, 11, 13 harmonics), a method of switching the PWM a quarter of the period and the classical method of PWM. In symmetric modes of the most effective method SHE PWM with five switching quarter period. When the supply voltage unbalance similar results give the classic method of PWM and SHE PWM method with nine switching quarter period. The application of these methods in single-ended modes rather than the other.

Single and Multi Optical Soliton Light Trapping and Switching Using Microring Resonator

We propose a system of microring resonator (MRR) incorporating with an add/drop filter system under nonlinearity condition where trapping of single and multi optical soliton can be simulated and used to many applications in optical switching and signal processing. Nonlinear Kerr effect type of the light inside the MRR induces the chaotic behavior within the device. By using appropriate soliton input power and MRR parameters, continuous spatial and temporal signals are generated spreading over the spectrum. In this work, narrow single and multi pulse of solitons can be trapped within the proposed system. There are two forms of localized soliton pulses as spatial and temporal in which required security can be performed via ultra-short pulses of soliton where the high capacity can be obtained using multiple trapping techniques. Results obtained show that single temporal and spatial soliton pulse of 4.8 picosecond (ps), 17.5 picometer (pm), 712 femtosecond (fs), 0.34 nanometer (nm) and 84 fs could be trapped where multi soliton pulses with FSR of 1.45 nm, 3.6 nanosecond (ns) and FWHM of 40 pm, 140 ps are localized within the add/drop filter system.

Simulation Study on Multi-Pulse Phenomena of Atmospheric Pressure Argon Dielectric Barrier Discharge

In this paper, a one-dimensional discharge model is employed to study multi-pulse phenomena in Ar dielectric barrier discharge (DBD) under atmospheric pressure. The finite-element method is employed to solve the model. The influences of applied voltage amplitude and frequency as well as gas gap distance on the variation of multi discharge pulses are investigated and discussed. The simulation results show that, both the intensity of discharge current and the number of discharge pulses increase with the amplitude of applied voltage, and narrower gas gap is more favorable for the formation of multi pulses. It is revealed that Ar DBDs behave in glow discharge mode when the applied voltage and gas gap distance vary from 2 kV to 6 kV and from 1 mm to 3 mm, respectively. With the frequency decreasing from 250 Hz to 125 Hz, the intensity of discharge current weakens and the number of discharge pulses increases, and the discharges behave in the typical Townsend discharge mode.

Study of femtosecond ablation on aluminum film with 3D two-temperature model and experimental verifications

In this paper, a 3D two-temperature model is introduced to investigate femtosecond ablation on aluminum film. 3D temperature evolutions for both electrons and lattice are obtained, which present us a vivid view of the energy transformation process during femtosecond ablation. Simulated 3D ablation craters irradiated by a single pulse with different energy are acquired, from which we can easily and precisely predict crater depth and radius before ablation takes place. In the experiment we measure the radii of the craters ablated by pulses with different energy and numbers delivered from a chirped pulse amplification Ti: sapphire system. The threshold fluence for both single and multi pulses are obtained. Comparisons are made between results of the experiment and relative simulated calculations show the reliability of our proposed calculation model.

Dependence of Z-scan measurements on the spatiotemporal pulse parameters

We report the experimental results obtained by the closed-aperture Z-scan technique where Nd:YAG minilaser short pulses with different temporal pulse shapes have been used. It is shown that the nonlinear refractive index coefficient n2 of fused silica (one of the smallest among the condensed media) can be successfully measured using the pulses with durations of about 1 ns and energies less than 1 mJ. Very good compatibility between the values for the same samples of fused silica is obtained only if the temporal shapes of the used SBS-compressed, single longitudinal or multi longitudinal mode pulses are properly taken into account. It is also shown that spatial properties of the used beams should be taken account of properly. By these experiments we emphasize the significance of taking into account the temporal pulse shape profile for accurate determination of the nonlinear refractive index by the Z-scan technique. Keywords: Z-scan, pulse shape, nonlinear refractive index, fused silica

Generation of DSA for Security Application

A novel system of dark soliton array (DSA) for secured communication generated by using the multiplexed dark soliton pulses is proposed. The multi soliton pulses with relevant parameters are input into the micro ring resonators system with the radii of 10μm and 5μm. The dynamic dark solitons can be controlled and generated. The DSA are obtained by using a series micro ring resonators with parameters where in the wavelength range of _1 is 15016nm, _2 is 1518nm and _3 is 1520nm. For security applications, the DSA can be tuned and amplified. Thus, the use of DSA for high capacity transmission can be realized by using proposed secured system. In transmission, the long distance link of the multi variable network can be performed by this DSA.

Selective Patterning of ITO on flexible PET Substrate by 1064 nm picosecond Laser

Pulsed picosecond laser ablation of indium tin oxide (ITO) coated on flexible polyethylene terephthalate (PET) substrate has been investigated. Pulses with 355nm, 532nm and 1064nm wavelengths are performed for comparison. Laser irradiation from the front side and the back side are analyzed. The single pulse ablation threshold is found at 0.56J/cm2 from the study of the spot sizes varied according to pulse fluence. The overlap rate in multi pulses ablation of ITO layer is discussed during the scribing of lines. Optical microscopy, SEM, surface stylus and EDX analysis reveal that the ITO layer can be completely removed with little damage of the PET substrate using optimized parameters.

New Communication Bands Generated by Using a Soliton Pulse within a Resonator System

We propose a novel system of a broadband source generation using a common soliton pulse (i.e. with center wavelength at 1.55 ?m) propagating within a nonlinear microring and nanoring resonators system. A system consists of a micro ring resonator system incorporating an add/drop filter, whereas the large bandwidth signals can be generated, stored and regenerated within the system. By using the appropriate parameters relating to the practical device such as micro ring radii, coupling coefficients, linear and nonlinear refractive index, we found that the obtained multi soliton pulses have shown the potential of application for dense wavelength division application, whereas the different center wavelengths of the soliton bands can be obtained via the add/drop filter, which can be used to increase the channel capacity in communication network.

Multi‐soliton generation using a micro ring resonator system for DWDM based soliton communication

AbstractWe propose a new optical system that can be used to form the multi soliton pulses within the micro ring resonators. The system consists of two micro ring resonators and an add/drop multiplexer that can be integrated into a single system. The large bandwidth signal is generated by using a soliton pulse propagating in a Kerr type nonlinear medium. The tuned soliton pulses in either spatial or temporal modes are obtained by using the add/drop multiplexer. Results obtained have shown that the multi soliton pulses can be localized coherently within the micro ring waveguide. This is shown that the generation of the multi soliton pulses within the micro ring resonator is achieved, which is available for long distance communication with dense wavelength division multiplexing (DWDM). A significant increase in channel number and spacing is obtained, and the large free spectrum range (FSR) of 600 pm is achieved. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1374–1377, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24299

Ultrahigh-Speed Camera Study of a Plasma Source for a Repetitive and Miniature POS

The plasma opening switch (POS) is the fastest opening switch available for use in high-power pulsed systems. The present study reported in this paper arose during the development of a compact and repetitive radiation generator, in which a POS is to be used to produce very fast rising high-voltage multi gigawatt pulses. Since the present POS requires a relatively low opening current, which is about 50 kA with a rise time of about 50 ns, a careful study was required to ensure that the proper plasma conditions (such as density and velocity) were generated by the simultaneous operation of a number of plasma guns. Initially, a Faraday cup-based technique established accurately most of the plasma parameters produced by a single gun (density:1013 cm-3 ; velocity: 2.2 cm/mus ). However, an optical study, which is mainly based on picture frames taken by an ultrahigh-speed camera, was also necessary to obtain the overall dynamics of the plasma generated by a set of four guns. Principle results are presented.

Generation of Optional Pulse Shape by Yb Doped Fiber Laser System

We have demonstrated the generation of optional pulse shape by Yb doped fiber laser system. Yb fiber laser system operated the polarization-maintained pulsed at 1064 nm for single-transverse and -longitudinal mode using fiber Bragg grating (FBG), and this system generates optional pulse shapes that sliced up the Yb fiber oscillator by a LN (LiNbO3) intense modulator with 12.5-GHz bandwidth. The developed electronic-pulseshape generator supplies an arbitrary-voltage pulse to an integrated optic LN amplifier modulator which modulates the laser pulse. The output laser waveforms can obtain corresponding to the electronic waveforms such as rectangular, Gaussian and multi pulses with a 300-ps resolution.