Parabolic Self-similar Pulses Research Articles

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.

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.

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.

Pulse generation without gain-bandwidth limitation in a laser with self-similar evolution.

With existing techniques for mode-locking, the bandwidth of ultrashort pulses from a laser is determined primarily by the spectrum of the gain medium. Lasers with self-similar evolution of the pulse in the gain medium can tolerate strong spectral breathing, which is stabilized by nonlinear attraction to the parabolic self-similar pulse. Here we show that this property can be exploited in a fiber laser to eliminate the gain-bandwidth limitation to the pulse duration. Broad (∼200 nm) spectra are generated through passive nonlinear propagation in a normal-dispersion laser, and these can be dechirped to ∼20-fs duration.

一种基于两段光纤链路的抛物自相似脉冲压缩方法

一种基于两段光纤链路的抛物自相似脉冲压缩方法

基于非线性渐增原理获得抛物线型自相似脉冲的研究

基于非线性渐增原理获得抛物线型自相似脉冲的研究

Efficient dispersion tailoring by designing alternately arranged dispersion compensating fibers and fiber amplifiers to create self-similar parabolic pulses

The parabolic similariton pulse formation by alternate arrangements of passive and active dispersion compensating fibers (DCFs) is presented here. These combinations of passive and active DCFs with constant core radii and constant nonlinearities are suggested as equivalent profiles of a dispersion tailored fiber amplifier in normal dispersion regime. The dispersion tailored fibers, usually known as dispersion decreasing fibers (DDFs) in normal dispersion regime, are capable of producing linearly chirped parabolic self-similar pulses. The DDF is designed and optimized with proper choice of fiber parameters so that considerable variation of nonlinearity can be achieved, which in turn enhances the effective gain coefficient of the fiber. Inclusion of this nonlinear variation along the DDF amplifier length leads to obtain the simulated output pulses with very small misfit parameters with respect to perfect parabolic pulse at sufficiently reduced optimum length. At the same time to avoid the fabrication difficulties of the DDF, the alternately arranged passive and active DCFs are suggested as suitable alternatives of the DDF. The performances of the cascaded systems for generation of self-similar parabolic pulses are compared with that of the DDF amplifier as well as combined systems consisting of DCFs with equal gain. The results show that the proposed alternately arranged cascaded system with less pumping requirements, are efficient enough to produce similar parabolic pulses as compared to the previously designed DDF, even when considerable amount of splice loss at each joint is included.

Dispersion managed self-similar parabolic pulses

We describe the propagation of a parabolic self-similar pulse in an anomalous dispersive nonlinear fibre. Given the capacity of a linearly chirped parabolic pulse to retain its typical shape over a short propagation distance, we introduce the concept of dispersion managed self-similar pulses and outline potential benefits in terms of spectral broadening enhancement.