Effects of high-order dispersions on dark-bright vector soliton propagation and interaction

The dynamics of dark-bright vector solitons is investigated in a birefringent fiber with the high-order dispersions,and their effects on vector soliton propagation and interaction are analyzed using the numerical method.The combined role of the high-order dispersions,such as the third-order dispersion (TOD) and the fourth-order dispersion (FOD),may cause various deformation of the vector soliton and enhance interaction.These effects depend strictly on the sign of the high-order dispersions.Results indicate that the disadvantageous effects can be reduced effectively via proper mapping of the high-order dispersions.     

色散缓变光纤中飞秒孤子压缩与稳定传输

运用数值方法研究了色散缓变光纤中飞秒基本孤子的传输特性，发现基本孤子脉冲不仅能被压缩，而且压缩光脉冲能保持脉宽不变转输即稳定传。光脉冲压缩过程中，发现三阶色散效应有较大的影响。适当地选取色散缓变光纤结构参数可能获得高质量的超短压缩光脉冲。对压缩光脉冲稳定伟机理探索表明，光纤二阶色散纵向变化率，三阶色散与喇曼自散射效应共同作用导致压缩光脉冲稳定传输。     

Dark Bound Solitons and Soliton Chains for the Higher-Order Nonlinear Schrödinger Equation

Dark bound solitons and soliton chains without interactions are investigated for the higher-order nonlinear Schrödinger (HNLS) equation, which can model the propagation of the femtosecond optical pulse under some physical situations in nonlinear fiber optics. Via the modulation of parameters for the analytic solutions, different types of dark bound solitons and soliton chains can be derived for the HNLS equation. In addition, stabilities of those structures are checked through numerical simulations. Our discussions are expected to be helpful in interpreting those new structures, and applied to the long-distance transmission of the femtosecond pulses in optical fibers.     

色散缓变光纤对飞秒基孤子的压缩效应

本文报道飞秒光脉冲在色散缓变光纤中的传输特性研究,首次研究自变陡效应、喇曼自频移效应分别对飞秒弧子压缩的影响。选取色散缓变光纤结构参数,可以得到脉宽为10飞秒的高质量(无底座)的超短光脉冲。     

Third- and fourth-order active dispersion compensation with a phase modulator in a terabit-per-second optical time-division multiplexed transmission

Broadening of the pulse waveforms by the higher-order dispersion of a transmission line is a critical limiting factor in achieving terabit-per-second optical time-division multiplexed (OTDM) transmission with femtosecond pulses. We show that the third- and fourth-order dispersion of a transmission line can be simultaneously compensated for by use of a phase modulator. In this method, sinusoidal phase modulation applied to the linearly chirped pulse before transmission compensates for the phase shift caused by the third- and fourth-order dispersion of the transmission line. The pulse broadening of a 380-fs pulse after a 70-km transmission in a 1.28-Tbit/s OTDM experiment was as small as 20 fs.     

Soliton formation in the propagation of phase-modulated femtosecond pulses through an optical fiber with a cubic nonlinearity

A way of soliton self-formation upon propagation of femtosecond light pulses through an optical fiber with a cubic nonlinearity is described with allowance for the dispersion of the nonlinear response of the medium. For soliton formation to occur, a low-frequency phase modulation of the initial pulse is necessary. Several solitons formed in this way differ in both maximal intensities and group velocities. The duration of an individual soliton may be several (up to ten) times smaller than the initial duration of the input pulse.     

高阶效应对光纤系统中孤子和艾里脉冲传输特性影响的数值研究

以变系数耦合高阶非线性薛定谔方程为理论模型,采用分步傅里叶方法,讨论了孤子和艾里脉冲在光纤中的传输特性。研究表明三阶色散、自频移和自陡峭效应导致孤子和艾里脉冲所分离出的俘获孤子的中心位置发生偏移,且三阶色散会影响俘获孤子的强度,并讨论了两脉冲的中心位置及强度对艾里脉冲截断系数的依赖关系。     

Sub-100 fs SDPF optical soliton compressor for diode laser pulses

We report our studies on a fiber-optic soliton compressor for generation of sub-100 femtosecond (fs) optical pulses out of picosecond (ps) diode laser pulses. The soliton compressor is rather simple and composed of a 15 ～ 20 m-long step-like dispersion profiled fiber (SDPF) in conjunction with a single Er-doped fiber amplifier (EDFA). Careful design of such a SDPF compressor was performed, leading to demonstration of 20-fs class compression performance, and experimental investigation was carried out in detail on the optical pulse propagation in the compression processes. In addition, nonlinear fiber loops were applied to suppression of pulse pedestals, resulting successfully in high quality optical pulses of the 100-fs range.     

Combined nonlinear effects for UV to visible wavelength generation in a photonic crystal fiber

We experimentally study the combined nonlinear effects,including four-wave mixing,stimulated Raman scattering,soliton dynamics,and cross-phase modulation by coupling femtosecond pulses around 850 nm into the normal dispersion region near the zero-dispersion wavelength in the fundamental mode of a homemade silica photonic crystal fiber. The nonlinear optical dynamics at different stages are demonstrated,and the discrete ultraviolet(UV) to visible wavelengths widely separated from the pump wave are generated by the interaction of several nonlinear effects involved. The UV to visible wavelengths can be used as short pulse sources for multiphoton ionization,fluorescence spectroscopy,and biochemical imaging.     

Self-action of light beams in nonlinear media: soliton solutions

The behaviour of light beams in nonlinear media (self-focussing of optical beams as well as self-modulation and transmission of optical pulses) is considered in the case when the nonlinear polarization contains susceptibilities of third- and fifth-order. The soliton solutions are obtained for the nonlinear equations deduced.     

四阶色散对飞秒高斯脉冲传输的影响

推导了考虑二、三、四阶色散的高斯脉冲传输方程;利用计算机数值模拟的方法,研究了四阶色散(FOD)对飞秒高斯脉冲在单模光纤中传输特性的影响.模拟结果显示：只有在入射脉冲宽度窄到飞秒量级时,即对应传输速率很高的情况下,FOD对脉冲的影响才明显;FOD导致脉冲形状发生了畸变,畸变特点不同于二、三阶色散;随着初始脉宽逐渐减小,FOD所致的飞秒高斯脉冲畸变经历了一个脉冲仅仅展宽,到展宽脉冲的两翼出现“底座”,到展宽脉冲的两翼出现具有微小振荡“底座”的变化过程.     

Breathers and localized solitons for the Hirota–Maxwell–Bloch system on constant backgrounds in erbium doped fibers

In nonlinear erbium doped fibers, the Hirota–Maxwell–Bloch system with higher order effects usually governs the propagation of ultrashort pulses. New soliton solutions for this system are constructed on the constant backgrounds including one and two breathers and first and higher order localized soliton solutions. Considering the influence of higher order effects, propagation properties of those soliton solutions are discussed.     

飞秒强激光脉冲在等离子体中的自压缩

文章从激光等离子体相互作用的非线性薛定谔方程出发,理论研究了飞秒强激光脉冲在等离子体中的自压缩行为.结果表明在一定范围内随着激光脉冲宽度、激光强度的增大以及等离子体密度的减小,飞秒强激光脉冲在等离子体中传播的自压缩现象越明显.另外通过适当设定参量得到了近似稳定传播的基孤子.     

Highly nonlinear optical fibre loop mirror for reshaping femtosecond pulses from a soliton-compressed electro-absorption modulator source over a wide repetition rate and wavelength range

Highly nonlinear fibre (HNF) applied to a nonlinear optical fibre-loop mirror (NOLM) proves very effective for high quality femtosecond pulses shaping. The HNF exhibiting about four times larger nonlinearity than either dispersion flattened fibre or dispersion-shifted fibre excites higher-order soliton propagation enabling significant pulse compression, while shortening the loop length required for efficient switching, which advantageously reduces both the detrimental higher-order chromatic dispersion effects and sensitivity to environmental perturbations. A short NOLM consisting of a 60 m HNF demonstrates effective reshaping and compression of 254–394 fs pulses from a fibre-soliton compressed electro-absorption modulator source to produce pedestal-free and transform-limited 186–243 fs pulses over a wide wavelength (1550–1570 nm) and repetition-rate (6.8–18 GHz) range.     

较高阶非线性抽运-探测过程中的空间效应

在飞秒抽运一探测光谱技术中,空间分辨的探测光信号反映了在不同空间位置的材料的非线性效应。当抽运光强度增大时,探测光信号中会出现明显的高阶特别是五阶非线性效应。利用劈裂算子方法直接解决了一维非线性传播方程的问题。在数值模拟中,研究了在不同抽运强度和位置下的抽运一探测过程中的五阶非线性效应。在足够高的抽运场下,探测信号出现清晰的振荡,显示了三阶和五阶非线性效应之间的干涉。当空间位置离抽运场中心足够远时,五阶比三阶非线性效应的衰减快得多,对其物理机制和趋势进行了定性的讨论。     

Amplitude and phase measurements of femtosecond pulse splitting in nonlinear dispersive media

Frequency-resolved optical gating is used to characterize the propagation of intense femtosecond pulses in a nonlinear, dispersive medium. The combined effects of diffraction, normal dispersion, and cubic nonlinearity lead to pulse splitting. The role of the phase of the input pulse is studied. The results are compared with the predictions of a three-dimensional nonlinear Schr?dinger equation.     

周期量级飞秒脉冲电场在非线性克尔介质中的传输

采用时间转换法研究了周期量级飞秒脉冲电场在非线性克尔介质中的传输.由于周期量级飞秒脉冲电场的脉宽小于介质拉曼响应的特征时间,在传输过程中脉冲电场会发生剧烈的变形和分裂,并在频谱上观察到了强烈的拉曼感应频移和色散波.由于周期量级脉冲电场依赖于载波包络相位,发现在脉冲电场传输过程中,主脉冲电场和色散波电场的相位线性地依赖于初始脉冲的载波包络相位.     

Control of interaction between femtosecond dark solitons in inhomogeneous optical fibers

In this paper, we present exact femtosecond one- and two-dark soliton solutions for a variable-coefficient higher-order nonlinear Schrödinger equation via modified Hirota method. The propagation and interaction of femtosecond dark solitons are investigated in inhomogeneous fiber systems. Elastic collision, bound oscillation and parallel propagation can be achieved in both Gaussian distributed parameter system and exponentially periodic distributed parameter system by choosing the appropriate distributed parameters and soliton parameters. The results may be beneficial to the realization of interaction control of femtosecond dark solitons in communication systems.     

Adaptive control of femtosecond pulse propagation in optical fibers

Nonlinear effects present fundamental obstacles to the propagation of femtosecond pulses of detectable energy in single-mode optical fibers, inducing severe distortion even after a very short (a few meters) propagation distance. We show here that adaptive pulse shaping can overcome these limitations by synthesizing pulses that are self-correcting for higher-order nonlinear effects when they are launched in the fiber. This approach would not only affect optical communications but also yield benefits in various disciplines requiring optimized fiber-based femtosecond pulse delivery, for example, nonlinear imaging techniques such as multiphoton microscopy, material processing, and medical diagnostics.