Generation of excellent self-similar pulses in a dispersion-decreasing fiber

Pulses compression has been widely studied for a long time. In order to generate excellent self-similar pulses in a dispersion-decreasing optical fiber with normal group-velocity dispersion, the influence of initial pulse parameters on the properties of the self-similar parabolic pulses interaction are firstly investigated in the paper. We find that the phase of sinusoidal fit and asymptotic dark soliton change according to the changing of initial phase difference. Meanwhile, increasing the full-width at half-maximum and input energy or decreasing time-delay properly, the interaction between self-similar pulses enhances accordingly, which makes the interaction length shorter and reduce the lose of energy, resulting in high energy output. The results are beneficial in experimental studies by adjusting the initial parameters of pulses to generate high-quality self-similar pulse. It is important for Dense Wavelength Division Multiplexing (DWDM) transmission system which is in heavy demands of light source in wide-range wavelength.     

Parabolic pulse generation in a dispersion-decreasing solid-core photonic bandgap Bragg fiber

We analyze the interplay of nonlinearity and dispersion in a dispersion-decreasing photonic bandgap Bragg fiber as a new platform for generating parabolic pulses. A suitably designed linearly tapered, low-index-contrast, solid-core Bragg fiber - amenable to fabrication by conventional modified chemical vapor deposition technology - is shown to yield stable parabolic pulses. The fiber design was optimized through a simple and accurate transfer-matrix formalism and pulse evolution was studied by the well-known split-step Fourier method. Our study revealed feasibility of generating parabolic pulses in such a dispersion-decreasing Bragg fiber of length as short as 1 m. We have also studied the effect of third order dispersion on generated parabolic pulse, which is an important deteriorating factor in such applications. The effective single-mode operation of the proposed device is achieved through appropriate tailoring of the outer cladding layers.     

超短脉冲激光与钾原子的相互作用

采有耦合和非耦合表象,描述了超短脉冲激光与钾原子的相互作用。分析了进一步 激发光电离的过程,导出了跃迁终态随激光偏振组合的密切关键。     

利用ND-DDF放大器获得更佳线性啁啾抛物线脉冲

基于在正常色散渐减光纤（ND-DDF）或者正常色散光纤放大器，获得线性啁啾抛物线脉冲，提出并分析了利用ND-DDF放大器获得线性啁啾抛物线脉冲的优化方案．数值研究结果表明：与用ND-DDF或者正常色散光纤放大器获得线性啁啾抛物线脉冲的方案相比，利用ND-DDF放大器获得的抛物线脉冲的线性啁啾更为明显；研究还发现，增益影响着线性啁啾的大小和质量．计算表明，利用ND-DDF放大器产生的抛物线脉冲经啁啾补偿后可获得更大的压缩因子和更高的峰值功率．     

Distortion of parabolic pulse due to higher-order effects in a dispersion-decreasing fiber

Considering Third-order Dispersion (TOD) and Stimulated Raman Scattering effect (SRS) simultaneously, the properties of the self-similar parabolic pulse evolution in a dispersion-decreasing optical fiber with normal group-velocity dispersion are firstly investigated in our paper. Our results show that parabolic pulses are distorted and the characteristic of exactly self-similarity will be lost due to the High-order effects. When only the TOD is taken into account, the chirp still reveals highly linear but glows into asymmetric which causes the waveform appearing optical wave breaking. When only considering SRS, the pulse still reveals highly linear chirp only linearity range narrow down, resulting in delaying the self-similar evolution. When considering SRS and TOD simultaneously, parabolic pulses are distorted less and the characteristic of exactly self-similarity will be better due to SRS effect than only considering TOD effect. The highly linear chirp in optical pulse still allows for efficient and high-quality pulse compression by use of dispersion compensation technique.     

色散渐减光纤的脉冲压缩研究

介绍了色散渐减光纤的绝热孤子压缩(ASC)过程，分析结果表明利用线性渐减的色散渐减光 纤(DDF)对飞秒基态孤子进行绝热压缩可以得到高质量的压缩脉冲，但用于压缩的DDF长度很 长，因此又提出DDF的高阶孤子(1＜N≤21)脉冲压缩技术，以在较短的DDF长度下获得 较大压缩比和高质量的压缩脉冲. 关键词： 色散渐减光纤 绝热孤子压缩 脉冲压缩 高阶孤子     

色散渐减光纤中的脉冲展宽研究

讨论了高斯脉冲在五种不同群色散剖面光纤中的传播特性和初始啁啾对脉宽的影响。结果发现:与单模光纤相比,色散渐减光纤(DDF)中的脉冲展宽较慢,并能有效抑制展宽,当β2C>0时,脉冲展宽速度与无啁啾时相比较快,当β2C<0时,脉冲有一初始窄化过程,不同群色散函数对啁啾脉冲有不同的影响。     

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.     

Femtosecond parabolic pulse nonlinear compression with gas-filled hollow-core fiber

We study theoretically the spectral intensity evolutions of the femtosecond Gaussian and parabolic pulses with different initial pulse energies and compare the nonlinear compressions of these pulses based on a meter-long hollow-core fiber filled with neon for different initial pulse durations. The pulses are first coupled into gas-filled hollow-core fiber for spectrum broadening, then compressed by the optimal chirp compensation. The parabolic pulse possesses a shorter pulse duration, larger peak power, and cleaner wings than Gaussian pulse. The properties are useful for compressing the pulses and thus generating the high-energy, short-duration pulses.     

Distortion of ultrashort laser pulses in a spatial filter

By means of Collins diffraction integral, the propagation expression of an ultrashort laser pulse passing through a spatial filter is derived. The effects of the magnification of spatial filter on pulse broadening and distortion of pulse-front for the ultrashort optical pulse are analytically deduced and numerically simulated. It is found that pulse broadening and propagation time difference of a laser pulse getting through spatial filter is proportional to the magnification. As a conclusion, in an ultrashort pulse laser system with a large aperture, the effect of pulse broadening and distortion of pulse-front should be considered.     

Interaction of a parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser

We numerically investigate the formation and interaction of a parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser. Based on a lumped model, the parabolic-shaped pulse pair is obtained by controlling the intercavity average dispersion and gain saturation energy, Moreover, pulse repulsive and attractive motion are also achieved with different pulse separations. Simulation results show that the phase shift plays an important role in pulse interaction, and the interaction is determined by the inter-cavity average dispersion and gain saturation energy, i.e., the strength of the interaction is proportional to the gain saturation energy, a stronger gain saturation energy will result in a higher interaction intensity. On the contrary, the increase of the inter-cavity dispersion will counterbalance some interaction force. The results also show that the interaction of a parabolic-shaped pulse pair has a larger interaction distance compared to conventional solitons.     

Interaction of parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser

We numerically investigate the formation and interaction of parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser. Based on a lumped model, the parabolic-shaped pulse pair is obtained by controlling the inter-cavity average dispersion and gain saturation energy, Moreover, pulse repulsive and attractive motion are also achieved with different pulse separations. Simulation results show that the phase shift plays an important role in pulse interaction, and the interaction is determined by the inter-cavity average dispersion and gain saturation energy, i.e., the strength of the interaction is proportional to the gain saturation energy, the stronger gain saturation energy will result in higher interaction intensity. On the contrary, the increase of the inter-cavity dispersion will counterbalance some interaction force. The results also show that the interaction of a parabolic-shaped pulse pair has a larger interaction distance compare to the conventional solitons.     

Dynamics of parabolic pulses in an ultrafast fiber laser

We report experimental and numerical results on the dynamics and propagation of parabolic pulses in a passively mode-locked ytterbium-doped fiber laser. Experimental data and numerical simulations are shown to match. Particular importance is attached to the pulse-shaping process in the different sections of the resonator. The paramount role of the gain fiber and saturable absorber in the laser is explicated.     

Formation of parabolic pulses in inhomogeneous fiber optical amplifiers

The conditions for forming pulses with parabolic envelope asymptotics in inhomogeneous fiber optical amplifiers are investigated. The profile of normal group-velocity dispersion, which ensures formation of parabolic pulses with a reduced rate of frequency modulation, is determined. It is shown by numerical simulation that the presence of chirp in the input pulse may cause narrowing of the spectrum at a certain energy.     

Heat capacity and entropy of two electrons quantum dot in a magnetic field with parabolic interaction

The thermodynamic properties of two electrons in two dimensional parabolic GaAs quantum dot are studied where both the magnetic field and the e–e interaction are fully considered. The e–e interaction has been treated by a model potential which makes the Hamiltonian exactly solvable. The energy spectrum is used to calculate the canonical partition function, and then we obtain the thermodynamic properties; mean energy, heat capacity and entropy as a function of temperature (T) and magnetic field (B).A steep transition from zero to 4k_B is observed in the heat capacity as a function of temperature for small values of magnetic field and saturates within a small temperature range, also the heat capacity has a peak-like structure at low temperature, while for high magnetic field heat capacity develops a shoulder at 2k_B then it approaches the saturation value with further increase in temperature. The entropy increases with increasing temperature, but at higher temperature, it remains almost independent of the magnetic field. It is shown that, at low magnetic field values, the effect of magnetic field on heat capacity is tangible and it attains a constant value with further increase in magnetic field. Entropy is almost linearly proportional with increasing magnetic field strength.     

Experimental study on generation of high energy few cycle pulses with hollow fiber filled with neon

25 fs pulses with energy up to 0.8 mJ from a multi-pass amplifier system have been spectrally broadened from 460 nm to 950 nm due to strong self-phase modulation (SPM) effect in a gas filled hollow fiber. Using a set of chirped mirrors, the ultra-broadband dispersion compensation was achieved, and the compressed pulses reached their transform limit. Under optimized conditions we achieved pulses with duration of 5.1 fs and with energy of 400 μJ, corresponding to the peak power up to 80 GW. Supported by the National Natural Science Foundation of China (Grant Nos. 60608003, 60490280, 60225005 and 60621063)     

The quantum acoustomagnetoelectric field in a quantum well with a parabolic potential

The acoustomagnetoelectric (AME) field in a quantum well with a parabolic potential (QWPP) has been studied in the presence of an external magnetic field. The analytic expression for the AME field in the QWPP is obtained by using the quantum kinetic equation for the distribution function of electrons interacting with external phonons. The dependence of the AME field on the temperature T of the system, the wavenumber q of the acoustic wave and external magnetic field B for the specific AlAs/GaAs/AlAs is achieved by using a numerical method. The problem is considered for both cases: The weak magnetic field region and the quantized magnetic field region. The results are compared with those for normal bulk semiconductor and superlattices to show the differences, and we use the quantum theory to calculate the AME field in the QWPP.     

飞秒激光脉冲在正色散固体材料中的自压缩

实验研究了正色散固体介质中的激光脉冲自压缩现象,证明了无需任何外加色散补偿情况下，固体透明介质中的自聚焦传输过程可使高功率飞秒激光脉冲实现时域脉冲压缩，并详细研究了输出脉冲的时域和频域特性随入射脉冲强度的演化规律.实验结果表明脉冲自压缩量随入射脉冲强度的增加呈递增趋势，然而当入射光强增大到足以引起超连续谱及锥形辐射产生时，脉冲时域形状会发生分裂.此外还发现发散光束入射情况下同样可以观察到脉冲自压缩现象. 关键词： 超短激光脉冲 脉冲压缩 非线性传输     

Self-similar propagation of high-power parabolic pulses in optical fiber amplifiers

Self-similarity techniques are used to study pulse propagation in a normal-dispersion optical fiber amplifier with an arbitrary longitudinal gain profile. Analysis of the nonlinear Schr?dinger equation that describes such an amplifier leads to an exact solution in the high-power limit that corresponds to a linearly chirped parabolic pulse. The self-similar scaling of the propagating pulse in the amplifier is found to be determined by the functional form of the gain profile, and the solution is confirmed by numerical simulations. The implications for achieving chirp-free pulses after compression of the amplifier output are discussed.     

Generation of few-cycle laser pulses:Comparison between atomic and molecular gases in a hollow-core fiber

We numerically study the pulse compression approaches based on atomic or molecular gases in a hollow-core fiber.From the perspective of self-phase modulation(SPM), we give the extensive study of the SPM influence on a probe pulse with molecular phase modulation(MPM) effect. By comparing the two compression methods, we summarize their advantages and drawbacks to obtain the few-cycle pulses with micro- or millijoule energies. It is also shown that the double pump-probe approach can be used as a tunable dual-color source by adjusting the time delay between pump and probe pulses to proper values.