Self-similar Pulses Research Articles

High Degree Picosecond Pulse Compression in Chalcogenide-Silicon Slot Waveguide Taper

In this paper, we propose and design a chalcogenide (As2S3)-based slot waveguide taper with exponentially decreasing dispersion profile to realize high-degree pulse compression of low-power chirped solitons. Based on the waveguide taper designed, pulse compression of fundamental solitons, and chirped 2-soliton breather are both investigated numerically. With self-similar pulse compression scheme, a 1 ps input pulse is compressed to 81.5 fs in 6 cm propagation. By using 2-soliton breather pulses, a 1 ps chirped pulse is compressed to 80.3 fs in just 2.54 cm. This is the first demonstration of the feasibility of high-degree nonlinear pulse compression in As2S3-based slot waveguide taper.

Study of parabolic self-similar optical pulse generation in single mode fibers using variational approximation for the LP01 mode

A number of single and two parameter variational approximations for the LP01 mode are reported in the literature which has been used to compute the various propagation characteristic parameters, such as, propagation constant, normalised dispersion, splice loss, bending loss etc. for single mode fibers. These studies are limited to optically linear fibers. To our knowledge, these variational approximations have not been used to study the nonlinear optical processes in such fibers. In the present work, using these variational approximations, the generation of self-similar parabolic pulses in graded-index single mode normal dispersive active fibers has been studied. The optimum length Lopt of the fiber, after which an input Gaussian pulse turns into a self-similar parabolic pulse, has been computed and the accuracies obtained from these variational approximations have been compared.

Influence of pumping schemes on the characteristics of self-similar pulses in a passively mode-locked fiber laser

Self-similar pulses are one of the domestic and international research hotspots in the field of nonlinear fiber optics because it can suppress optical wave breaking at high energies. The influence of pumping schemes on the characteristics of self-similar pulses in a passively mode-locked Yb-doped fiber laser is theoretically investigated. The temporal profile and optical spectrum of self-similar pulses in passively mode-locked fiber lasers of different pumping schemes are obtained in the simulation. This study focuses on analyzing the influence of gain bandwidth of gain fiber on the pulse duration, peak power, and single-pulse energy of self-similar pulses.

Self-similar pulse evolution in a fiber laser with a comb-like dispersion-decreasing fiber.

We demonstrate an erbium fiber laser with self-similar pulse evolution inside a comb-like dispersion-decreasing fiber. We show numerically and experimentally that the comb-like dispersion-decreasing fiber works as well as an ideal one, and offers major practical advantages. The existence of a nonlinear attractor is verified by the invariant pulse chirp over a wide range of net cavity dispersion in experiments. The laser generates 1.3 nJ pulses with parabolic shapes and linear chirps, which can be dechirped to 37 fs. Comb-like dispersion-decreasing fiber should enable the generation of high-energy few-cycle pulses directly from a fiber oscillator.

On the Efficiency of Parabolic Self-Similar Pulse Evolution in Fiber Amplifiers with Gain Shaping

We numerically and experimentally demonstrate the influences of gain fiber length, initial pulse center wavelength, duration, chirp, and temporal profile for efficient parabolic self-similar evolution, accounting for the strong gain shaping effect in fiber amplifiers under high gains. A spectrally resolved numerical model allowing for realistic descriptions of the variable wavelength-dependent gain is developed. The results predict the specific regions of the initial center wavelength and the duration for the self-similar evolution, which move toward a longer center wavelength and a broader duration range with the increasing gain fiber length. For short-length high-gain amplifiers, a proper negative initial chirp can not only resist the gain-shaping deformation and facilitate the self-similar evolution but also provide a broadband output. In addition, a triangular initial profile is found to be of minimum sensitivity to the detrimental gain shaping and optimum for efficient self-similar evolution. The experimental results confirm the numerical predictions. The studies of the fast parabolic pulse formation in short-length high-gain amplifiers presented here demonstrate the potential for performance scaling of femtosecond fiber amplifiers, few-cycle pulse sources, high-power frequency combs, and related applications.

Stable Similariton Generation in an All-Fiber Hybrid Mode-Locked Ring Laser for Frequency Metrology.

Ultrashort pulse lasers constitute an important tool in the emerging field of optical frequency metrology and are enabling unprecedented measurement capabilities and new applications in a wide range of fields, including precision spectroscopy, atomic clocks, ultracold gases, and molecular fingerprinting. We demonstrate the generation of stable 127-fs self-similar pulses at a central wavelength of 1560nm with 7.14-mW average output power. Similariton lasers have a low repetition rate deviation in the averaging time interval [Formula: see text], a low relative intensity noise [Formula: see text] (30Hz to 10kHz), a narrow single comb line width of 32kHz, and high reliability. Thus, such lasers are highly promising for further development of the stabilized combs and open up a robust and substantially simplified route to synthesizing low-noise microwaves.

Influence of gain coefficient on the self-similar pulses propagation in a dispersion-decreasing fiber

This paper first investigates the influence of the dispersion-decreasing optical fiber structure on the self-similar pulses interaction and compression. The dynamic of the evolution of a pair of self-similar pulses in a dispersion-decreasing optical fiber with normal group-velocity dispersion (ND-DDF) under different gain coefficient g0 of DDF is analyzed, and the chirp evolution is also studied to analyze the propagation characteristic of self-similar pulses. The numerical simulations show that the change of gain coefficient g0 of DDF can impact directly on the linear chirp of the self-similar pulses. We find out that the smaller g0 can generate better high-quality femto-second pulses than the higher g0 after pulses compression. Finally, we got a pair of ultra-short pulses with a FWHM of 124fs at g0=0.015m−1, indicating efficient and high-quality pulse compression.

Ultrafast fiber lasers based on self-similar pulse evolution: a review of current progress

Self-similar fiber oscillators are a relatively new class of mode-locked lasers. In these lasers, the self-similar evolution of a chirped parabolic pulse in normally-dispersive passive, active, or dispersion-decreasing fiber (DDF) is critical. In active (gain) fiber and DDF, the novel role of local nonlinear attraction makes the oscillators fundamentally different from any mode-locked lasers considered previously. In order to reconcile the spectral and temporal expansion of a pulse in the self-similar segment with the self-consistency required by a laser cavity’s periodic boundary condition, several techniques have been applied. The result is a diverse range of fiber oscillators which demonstrate the exciting new design possibilities based on the self-similar model. Here, we review recent progress on self-similar oscillators both in passive and active fiber, and extensions of self-similar evolution for surpassing the limits of rare-earth gain media. We discuss some key remaining research questions and important future directions. Self-similar oscillators are capable of exceptional performance among ultrashort pulsed fiber lasers, and may be of key interest in the development of future ultrashort pulsed fiber lasers for medical imaging applications, as well as for low-noise fiber-based frequency combs. Their uniqueness among mode-locked lasers motivates study into their properties and behaviors and raises questions about how to understand mode-locked lasers more generally.

Generation of 8 nJ pulses from a normal-dispersion thulium fiber laser.

We report a study of a mode-locked thulium (Tm) fiber laser with varying normal dispersion. It is difficult to reach the high-energy dissipative-soliton regime due to the anomalous dispersion of most fibers at 2 μm. With large normal dispersion, the laser exhibits elements of self-similar pulse evolution, and is the first Tm fiber laser to achieve the performance benefits of normal-dispersion operation. The laser generates 7.6 nJ pulses, which can be dechirped to 130 fs duration. The resulting peak power is 4 times higher than that of previous Tm fiber lasers.

Self-similar soliton-like solution for coupled higher-order nonlinear Schrödinger equation with variable coefficients

Self-similar soliton-like solution of a kind of coupled higher-order nonlinear Schrödinger equation with variable coefficients describing the optical soliton pulses propagating in inhomogeneous optical fiber media is investigated in this paper. The balance principle and the F-expansion technique are used to obtain the exact bright and dark self-similar soliton-like solutions analytically. As an example, we present a periodic distributed amplification system to investigate the pulse evolution characteristics by using the split-step Fourier method and the Runge–Kutta method. It is found that the self-similar soliton-like optical pulses can propagate stably in the given coupled system.

High-energy dissipative solitons generation from a large normal dispersion Er-fiber laser.

We report on a passively mode-locked erbium-doped fiber laser featuring a large normal dispersion and emitting high-energy dissipative solitons. Mode-locking is stabilized by the combined actions of a high nonlinearity amplitude modulator and a narrow band spectral filter. The laser routinely delivers highly chirped pulses with more than 38 nJ energy that can be compressed down to 700 fs duration using bulk gratings. Numerical simulations confirm the experimental results and reveal the self-similar pulse evolution along the normal dispersion fibers included inside the cavity.

Silica based highly nonlinear fibers to generate parabolic self-similar pulses

Three different silica based normal dispersion fibers are designed to identify the best possible one for efficient parabolic pulse generation. Two of them resemble commonly used single core fibers and optimized in such a way that one has lower dispersion and nonlinear coefficient whereas the other possesses higher dispersion and lower nonlinearity. A silica based multi-cladded highly nonlinear fiber (ND-HNLF) is designed as well by successfully restricting its effective area to a very lower value. The comparative analysis among the three fibers suggests that the ND-HNLF would be the best choice for fiber optic manufacturers for parabolic similariton formation due to its smaller optimum length, no effect of higher order dispersion, high nonlinearity and less input power requirement. From our proposed ND-HNLF, a highly nonlinear dispersion decreasing fiber (HN-NDDF) is also designed and optimized by properly varying different fiber parameters as a function of fiber length. Our study also reveals that the HN-NDDF with a typical property of virtual gain would be beneficial for producing parabolic self-similar pulses at smaller optimum lengths with adequate spectral broadening in comparison to that of ND-HNLF.

Dynamics of self-similar pulse generated in normal dispersion-decreasing fiber

Self-similar pulse can be generated in a normal dispersion-decreasing fiber. We show that the dynamics of self-similar pulse evolution is governed by the different spectrum broadening mechanisms in the different stages, which is confirmed by the typical pulse spectral structures with amplitude noise added.

Average cavity description of self-similar lasers

A purely analytical model treating an average cavity description of a passive self-similar optical resonator is developed. The model introduces an energy area theorem which provides an analytical framework for understanding energy scalability in passive self-similar systems. A qualitative link between self-similar pulses in fiber and solid state systems is explained by the analytical model through the nature of the saturable characteristics of the saturable absorber. The derived expressions for the field amplitude and chirp parameter of the pulse match well with simulation and offer insight into the mechanics of passive self-similar resonator design.

Self-similar erbium-doped fiber laser with large normal dispersion

We report a large normal dispersion erbium-doped fiber laser with self-similar pulse evolution in the gain fiber. The cavity is stabilized by the local nonlinear attractor in the gain fiber through the use of a narrow filter. Experimental results are accounted for by numerical simulations. This laser produces 3.5 nJ pulses, which can be dechirped to 70 fs with an external grating pair.

Study on the influences of system parameters on bound self-similar pulse pairs in a passively mode-locked fiber laser

This paper is devoted to research the characteristics of the bound self-similar pulses formed in a passively mode-locked Yb-doped fiber laser. The parabolic shape bound self-similar pulses with linear chirps are observed in the fiber laser. The influences of the small signal gain and the inter-cavity average group velocity dispersion (GVD) on pulse separation, pulse duration, peak power and single pulse energy of the bound self-similar pulse pairs are investigated in-depth. The simulation results contribute to the study of the stable transmission of bound state pulses.

Generation of parabolic similaritons in tapered silicon photonic wires: comparison of pulse dynamics at telecom and mid-infrared wavelengths

We study the generation of parabolic self-similar optical pulses in tapered Si photonic nanowires (Si-PhNWs) at both telecom (λ=1.55 μm) and mid-infrared (λ=2.2 μm) wavelengths. Our computational study is based on a rigorous theoretical model, which fully describes the influence of linear and nonlinear optical effects on pulse propagation in Si-PhNWs with arbitrarily varying width. Numerical simulations demonstrate that, in the normal dispersion regime, optical pulses evolve naturally into parabolic pulses upon propagation in millimeter-long tapered Si-PhNWs, with the efficiency of this pulse-reshaping process being strongly dependent on the spectral and pulse parameter regime in which the device operates, as well as the particular shape of the Si-PhNWs.

Self-similar soliton-like beam generation and propagation in inhomogeneous coupled optical fiber media system

In this paper, we present a theoretical model of coupled nonlinear Schrödinger equation with variable coefficients describing the self-similar soliton-like optical pulse propagating in the coupled inhomogeneous optical fiber system. The exact self-similar bright soliton-like solution and its propagation characteristics under different perturbation conditions are studied in detail. It is found that, within the range of appropriate parameters, stable propagation of the calculated self-similar bright soliton-like optical pulse can be obtained.

Nonlinear pulse reshaping in a designed erbium-doped fiber amplifier with a multicladded index profile

A multicladded normally dispersive erbium-doped fiber amplifier (ND-EDFA) is designed for a short length to operate at the wavelength of 1550 nm with a dispersion of −6.5 ps/km nm and parabolic pulse generation through the proposed fiber is studied. The proposed ND-EDFA shows a flattened gain spectrum in C -band. The nonlinear Schrödinger equation is solved numerically in presence of fiber gain, nonlinearity, and dispersion to investigate the pulse propagation through the proposed fiber. While continuous wave (CW) sources are considered, parabolic self-similar pulses with structure factor of 0.072 are created at suitable values of optimum fiber length when input pulse properties and fiber parameters are optimized accordingly. Side by side with a low repetition rate laser source, the pulse propagation equation is controlled by the gain dispersion term and dipole relaxation time, such that the evolution of Gaussian pulses may lead to nonparabolic regime. The effects of pulse parameters like power level, pulse width, and dipole relaxation time on the propagation of input Gaussian pulses through the so-designed ND-EDFA are investigated. Our results depict that the pulses with same input energy reshape into exactly parabolic shape for CW laser source or nonparabolic profile for a laser source with low repetition rate.

Generation of the self-similar parabolic pulses by designing comb-like profiled dispersion fiber based on alternately arranged single-mode fibers and dispersion-shifted fibers

Based on the nonlinear Schrödinger equation and the linearly chirped parabolic pulse generation in the dispersion decreasing fiber with normal dispersion, a novel scheme for the generation of the self-similar parabolic pulse via a comb-like profiled dispersion fiber with normal group-velocity dispersion has been proposed and the corresponding model is established. We study, analytically and numerically, the evolution of the self-similar parabolic pulse in comb-like profiled dispersion fiber with dispersion profile close to that of the dispersion decreasing fiber, and the influence of different initial energies and pulse widths on the linearly chirped parabolic pulse formation in the comb-like profiled dispersion fiber. The results show that the evolution of the self-similar parabolic pulses can realized in the comb-like profiled dispersion fiber, the results of which are in good agreement with these of the dispersion decreasing fiber, and the best-matched scheme of designing and optimizing comb-like profiled dispersion fiber will help to obtain the ideal similaritons.