光子晶体光纤耦合器中的标量调制不稳定性

从光纤耦合器的耦合模方程出发,用偶奇超模对其进行重写,讨论了当输入条件使奇偶超模其中之一被单独激发时,在光子晶体光纤耦合器中的调制不稳定性.结果表明：光子晶体光纤耦合器中在正常和反常色散区均存在调制不稳定性,并且调制不稳定性与三阶色散项无关、与四阶色散项有关,给出了增益谱在不同色散区随输入功率的变化关系;当满足一定条件时,在光子晶体光纤耦合器中传播的准连续波可以分解成脉冲序列,由此可以分离和提取超短脉冲. 关键词： 光子晶体光纤耦合器 偶次超模 奇次超模 标量调制不稳定性     

色散缓变光纤耦合器中的调制不稳定性

用奇偶超模对光纤耦合器的耦合模方程重写.讨论了当输入条件使奇偶超模其中之一被单独激发时,色散缓变光纤耦合器中的调制不稳定性,结合调制不稳定性,分析了色散缓变光纤耦合器在准连续波条件下的非线性效应.结果表明：在正常和反常色散区存在新型调制不稳定性.当满足一定条件时,在色散缓变光纤耦合器中传播的准连续波光束可以分解成脉冲序列,并且脉冲几乎不展宽,由此可以分离和提取稳定的超短脉冲;当输入功率一定时,增益谱随着传输距离的改变,形态基本保持不变;当传输距离一定时,增益谱随着输入功率的增强,宽度变宽,强度增强.     

色散缓变光纤中飞秒光脉冲的调制不稳定性研究

研究了色散缓变光纤中飞秒光脉冲的调制不稳定性 ,发现当色散缓变光纤的色散参量满足一定关系式时 ,增益谱的谱宽最宽 ,获得了增益谱的表达式 ;三阶色散对调制不稳定性不起作用 ;自变陡效应使增益谱的谱宽变窄 ,振幅的增长速度减漫 ;拉曼效应改变了调制不稳定性的产生区域。     

色散缓变光纤史飞秒光脉冲的调制不稳定性研究

研究了色散缓变光纤中飞秒光脉冲的调制不稳定性,发现当色散缓变光纤的色散参量满足一定关系式时,增益谱的谱宽最宽,获得了增益谱的表达式;三阶色散对调制不稳定性不起作用;自变陡效应使增益谱的谱宽变窄,振幅的增长速度减慢;拉曼效应改变了调制不稳定性的产生区域。     

局部高斯变迹布拉格光纤光栅中的调制不稳定性

利用激光脉冲在光纤光栅中传播时所遵守的相干耦合非线性薛定谔方程,研究了激光脉冲在局部高斯变迹布拉格光纤光栅中传输时,在反常色散区和正常色散区所产生的调制不稳定性。结果表明在反常色散区和正常色散区都能产生调制不稳定性;在反常色散区,当输入功率达到一定数值、传输距离一定时,当f=-1禁带之上能带底时,调制不稳定性增益的强度最强、宽度最窄;当远离能带底时强度减弱、宽度变宽;在正常色散区,在产生调制不稳定性功率区域,调制不稳定性存在并从给定值一直持续到无穷;并且,在反常色散区和在正常色散区,增益谱都受到局部高斯变迹函数的制约。     

高斯变迹布拉格光纤光栅中的调制不稳定性

利用激光脉冲在光纤光栅中传播时所遵守的相干耦合非线性薛定谔方程,研究了激光脉冲在高斯变迹布拉格光纤光栅中传输时，在反常色散区和正常色散区所产生的调制不稳定性.结果表明在反常色散区和正常色散区都能产生调制不稳定性；在反常色散区，当输入功率达到一定数值时，产生明显的有规律的增益谱；在正常色散区，在产生调制不稳定性功率区域，调制不稳定性存在并从给定值一直持续到无穷；并且，在反常色散区和在正常色散区，增益谱都受到高斯变迹函数的制约. 关键词： 高斯变迹 布拉格光栅 调制不稳定性 增益     

光子晶体光纤中调制不稳定现象与超连续光谱的产生

研究了光子晶体光纤中调制不稳定性效应.从非线性薛定谔方程出发，计算和分析了光子晶体光纤中反常色散区以及正常色散区内的调制不稳定性现象，详细讨论了超短脉冲的脉宽、峰值功率、高阶色散和高阶非线性效应（如脉冲内喇曼散射、自陡峭效应）对调制不稳定性产生的影响.结果表明：二阶色散对调制不稳定性的影响要远大于三阶色散，同时也发现随着初始脉冲宽度的减小，调制不稳定性旁瓣增大但是强度有所降低.另外还发现高阶非线效应如自陡峭和喇曼效应会在不同程度上抑制调制不稳定性.     

保偏光纤中相近频率传输区域的调制不稳定性

利用激光脉冲在光纤中传播时所遵守的相干非线性薛定谔耦合方程,研究了保偏光纤中两相近频率的线偏振光，其偏振方向相互正交且平行于光纤的双折射轴，且偏振方向沿两个双折射轴的分量强度相等时，在同为反常色散区和正常色散区所产生的调制不稳定性.结果表明在反常色散区和正常色散区都能产生调制不稳定性；在正常色散区存在不同的调制不稳定性功率区域，对应不同的功率区域，导致增益谱表现出明显的不同，并且当输入功率一定时，波长差(或频率差)的变化导致增益谱的变化. 关键词： 相近频率传输区域 双折射 保偏光纤 调制不稳定性     

具有高阶色散项的交叉相位调制不稳定性分析

以包含了三、四阶色散项的耦合非线性薛定谔方程为基础,重点研究了三、四阶色散对交叉相位调制不稳定性的影响。结果表明：三阶色散对调制不稳定性不起作用;当满足一定条件时,由于四阶色散的影响,不仅在光纤的反常色散区,而且在光纤的正常色散区,交叉相位所致的调制不稳定性均发生在两个频谱区。当光纤各参量及两束入射光波功率一定时,光纤反常色散区第一区域的增益谱要比正常色散区第一区域的增益谱宽;同时,反常色散区第二区域的增益谱比正常色散区第二区域的增益谱更靠近零点;进一步对比反、正常色散区的这两个频谱区,发现两个频谱区的范围有确定的对应关系。     

非线性高双折射阶跃光纤中单一频率传输区域调制不稳定性

利用光脉冲在高双折射非线性光纤中传播时所遵守的相干耦合非线性薛定谔方程,研究了单一频率的线偏振光,当偏振方向沿两个双折射轴的分量强度相等时,其在阶跃式光纤中反常色散区和正常色散区所产生的调制不稳定性。结果表明,调制不稳定性这一过程不仅产生在反常色散区,而且产生在正常色散区,对于阶跃式光纤,矢量调制不稳定性还随级数不同发生变化。并且,反常色散区产生的增益谱不同于正常色散区,较之多一个增益谱区域。     

Modulation Instability in Non-Kerr-like Optical Fibers near the Zero Dispersion Point

Modulation instability (MI) in non-Kerr-like optical fiber near the zero dispersion point is analyzed. Taking into account the fourth order dispersion, new regions of MI are found. The action of the self-steepening is not the same for each region of MI and critical modulation frequency.     

Modulation instability of femtosecond pulses in fibres with slowly decreasing dispersion

In this paper,we investigate the modulation instability for generating femtosecond pulses in fibres with slowly decreasing dispersion.Higher-order dispersion and higher-order nonlinear effects are taken into account when the continuous wave or quasi-continuous wave evolves into sub-picosecond and femtosecond pulses by modulation instability in the optical fibres.Our research results show that the gain spectrum of the dispersion-decreasing fibres is much wider than that in conventional fibres.The third-order dispersion effect has no contribution to gain spectrum,while the self-steepening effect reduces the maximum value and gain bandwidth,and the Raman self-scattering effect widens the extent to which the modulation instability occurs.     

各向同性光纤中拉曼增益对光脉冲自陡峭的影响

运用数学解析法导出了关于拉曼增益与自陡峭综合效应的光脉冲传输方程,在此基础上引入洛伦兹模型将拉曼增益整合到非线性系数中来研究光脉冲中拉曼增益对自陡峭效应的作用,重点分析了高斯脉冲在各向同性光纤中传播时,拉曼增益对其自陡峭效应具体影响方式,结果表明拉曼增益会减弱自陡峭中后沿偏移程度,减小脉冲展宽,但不会影响其峰值大小.     

Dark soliton switching in an NLDC in the presence of higher-order perturbative effects

Dark soliton switching in a nonlinear directional coupler in the presence of intermodal dispersion, cross-phase modulation (CPM), third-order dispersion, Raman effect, and self-steepening effect is reported for the first time. It is shown that, with the exception of CPM, all of the other perturbative effects have almost no effect on the switching characteristics of the dark soliton switch, which is an improvement over the corresponding bright soliton switch. Although the CPM increases the critical power of dark soliton switching, the soliton pulse remains stable inside the coupler during its propagation.     

Self-phase modulation via similariton solutions of the perturbed NLSE Modulation instability and induced self-steepening

The perturbed nonlinear Schrodinger equation (PNLSE) describes the pulse propagation in optical fibers, which results from the interaction of the higher-order dispersion effect, self-steepening (SS) and self-phase modulation (SPM). The challenge between these aforementioned phenomena may lead to a dominant one among them. It is worth noticing that the study of modulation instability (MI) leads to the inspection of dominant phenomena (DPh). Indeed, the MI triggers when the coefficient of DPh exceeds a critical value and it may occur that the interaction leads to wave compression. The PNLSE is currently studied in the literature, mainly on finding traveling wave solutions. Here, we are concerned with analyzing the similarity solutions of the PNLSE. The exact solutions are obtained via introducing similarity transformations and by using the extended unified method. The solutions are evaluated numerically and they are shown graphically. It is observed that the intensity of the pulses exhibits self steepening which progresses to shock soliton in ultra-short time (or near t = 0). Also, it is found that the real part of the solution exhibits self-phase modulation in time. The study of (MI) determines the critical value for the coefficients of SS, SPM, or high dispersivity to occur.     

Localized Optical Waves in Defocusing Regime of Negative-Index Materials

We study optical localized waves on a plane-wave background in negative-index materials governed by the defocusing nonlinear Schrodinger equation with self-steepening effect. Important characteristics of localized waves,such as the excitations, transitions, propagation stability, and mechanism, are revealed in detail. An intriguing sequential transition that involves the rogue wave, antidark-dark soliton pair, antidark soliton and antidark soliton pair can be triggered as the self-steepening effect attenuates. The corresponding phase diagram is established in the defocusing regime of negative-index materials. The propagation stability of the localized waves is confirmed numerically. In particular, our results illuminate the transition mechanism by establishing the exact correspondence between the transition and the modulation instability analysis.     

On the modulation instability development in optical fiber systems

Extensive numerical simulations were performed to investigate all stages of modulation instability development from the initial pulse of pico-second duration in photonic crystal fiber: quasi-solitons and dispersive waves formation, their interaction stage and the further propagation. Comparison between 4 different NLS-like systems was made: the classical NLS equation, NLS system plus higher dispersion terms, NLS plus higher dispersion and self-steepening and also fully generalized NLS equation with Raman scattering taken into account. For the latter case a mechanism of energy transfer from smaller quasi-solitons to the bigger ones is proposed to explain the dramatical increase of rogue waves appearance frequency in comparison to the systems when the Raman scattering is not taken into account.