Supercontinuum manipulation based on the influence of chirp on soliton spectral tunneling

The soliton spectral tunneling(SST) effect, as a soliton spectral switching phenomenon, enables a soliton to tunnel through a spectrally limited regime of normal dispersion in the fiber with multiple zero dispersion wavelengths(ZDWs).Since initial chirp can affect the behavior of pulse evolution, we numerically study the influence of chirp on the SST in the process of supercontinuum(SC) occurring in a photonic crystal fiber(PCF) with three ZDWs. The linear chirp is imposed by a phase modulation of input pulse while maintaining a constant pulse duration. Interestingly, it is found that the spectral range and flatness can be flexibly tuned by adjusting the initial chirp value. More specifically, positive chirp facilitates soliton self-frequency shifting(SSFS), making the soliton quickly transfer from one anomalous dispersion regime to another accompanied by the generation of dispersive waves(DWs). In this case, the SST effect further expands the spectral range by enhancing both the red-shift of the fundamental soliton and the blue-shift of DWs, thus generating a broader SC. However, negative chirp suppresses the SST effect, resulting in a smoother SC at the expense of bandwidth.Therefore, the findings in this work provide interesting results relating to the influence of initial chirp on the SST to generate a considerably smoother and broader SC, which is extremely useful in many applications, such as wavelength conversion and SC generation.     

Effect of dark soliton on the spectral evolution of bright soliton in a silicon-on-insulator waveguide

The spectral evolution of bright soliton in a silicon-on-insulator optical waveguide is numerically simulated using the split-step Fourier method. The power and input chirp of the dark soliton and the second-order dispersion are varied to investigate the effect of dark soliton on the spectrum of bright soliton. The simulations prove that the dark soliton modifies the spectral shape of the bright soliton. Further, the variation in the power of dark soliton affects the splitting of bright soliton. Furthermore, the chirped dark soliton can improve the spectral width and flatness. The variation in the dispersion of dark soliton modifies the phase matching of the bright soliton and the dispersive wave emission, thereby affecting the spectral evolution.     

Minimization of self-steepening of ultra short higher-order soliton pulse at 40 Gb/s by the optimization of initial frequency chirp

In this paper, the decay of first- and second-order ultra short pulses of the order of 50 fs due to self-steepening (SS) effect has been numerically investigated for a 40 Gb/s optical soliton system including the impact of third-order dispersion (TOD). It has been observed that the prechirp (both positive and negative) in the pulse can counteract the SS effect and improve compensation performance for the distortions .The critical positive prechirp value is found to be 1.4 and the negative prechirp is 1.2, beyond which the soliton pulse is unstable.     

Impact of higher-order effects on dissipative soliton in metamaterials

We study the influence of higher-order effects such as third order dispersion (TOD), fourth order dispersion (FOD), quintic nonlinearity (QN), self steepening (SS) and second order nonlinear dispersion (SOND) on the dynamics of dissipative soliton (DS) in metamaterials. Considering each higher-order effect as a perturbation to the system and following Lagrangian variational method, we demonstrate stable dynamics of DS as a result of the interplay between different higher-order effects. We also perform numerical analysis to confirm the analytical results.     

负折射介质中可控自陡峭效应对孤子传输的影响

研究了具有非线性极化的负折射介质中孤子脉冲的传输特性,着重分析了在常规非线性传输模型中不曾出现的由负折射介质色散磁导率导致的可控自陡峭效应对孤子传输的影响.结果表明,与正自陡峭效应一样,负自陡峭效应同样造成孤子脉冲的非对称、中心偏移和高阶孤子衰减,但脉冲偏移的方向与正自陡峭效应情形相反.此外,利用可控自陡峭效应可以从某种程度上抵消三阶色散效应导致的孤子脉冲偏移,从而实现孤子脉冲中心的无偏移传输.     

Self—Steepening and Thired—Order Dispersion Induced Optical Solitons in Fiber

Usually,one considers only the group velocity dispersion(GVD)-and self-phase modulation(SPM)-induced solitons in optic soliton communication while other higher order effects such as the third-order dispersion(TOD),self-steepening(SS),and stimulated Raman scattering are considered only perturbatively,In this paper,we study the existence of the TOD-and SS-induced soliton solutions.The existence conditions of the TOD-and SS-induced bright and dark solitons are quite different from those of the GVD-and SPM-induced solitons.     

飞秒脉冲在硅波导中产生超连续谱的研究

利用非线性薛定谔方程对飞秒脉冲在硅波导中的传输以及超连续谱的产生进行了研究,计算和分析了色散参量及非线性损耗在超连续谱的产生过程中的影响.结果表明,孤子分裂是飞秒脉冲在硅波导中产生超连续谱的主要机理.飞秒脉冲中心波长与波导零色散点的相对位置对超连续谱的产生有极大影响.当中心波长位于近零色散点的反常色散区时,孤子分裂现象最明显,谱宽远大于在零色散波长及正常色散处入射时的情况,并且达到稳定展宽所需波导长度最短.其次,高阶色散的大小也会影响光谱展宽,三阶色散绝对值较小时,能够获得较大的展宽.另外,由于双光子吸收效应带来大量损耗,限制了谱宽,并且随着初始脉冲功率的逐渐增大,展宽出现饱和现象. 关键词： 超连续谱 孤子分裂 色散 硅波导     

光孤子脉冲在光纤放大器中的传播

本文建立了包括增益色散,受激喇曼散射,双光子吸收效应的理论模型,讨论了光孤子脉冲在光纤放大器中的传播.数值计算结果表明:在反常色散范围内,光孤子的放大是不稳定的.增益色散导致光脉冲对称分裂,而受激喇曼散射则导致不对称的分裂.在增益色散和受激喇曼散射的共同作用下可获得新的时域和频域特征.有限带宽的放大能抑制受激喇曼散射引起的自频移.本文对有啁啾的光孤子脉冲的放大也进行了分析.     

Dissipative Kerr solitons in optical microresonators with Raman effect and third-order dispersion

Using the mean-field normalized Lugiato–Lefever equation, we theoretically investigate the dynamics of cavity soliton and comb generation in the presence of Raman effect and the third-order dispersion. Both of them can induce the temporal drift and frequency shift. Based on the moment analysis method, we analytically obtain the temporal and frequency shift,and the results agree with the direct numerical simulation. Finally, the compensation and enhancement of the soliton spectral between the Raman-induced self-frequency shift and soliton recoil are predicted. Our results pave the way for further understanding the soliton dynamics and spectral characteristics, and providing an effective route to manipulate frequency comb.     

光孤子对的振幅比与相位差对传输的影响

利用分步傅里叶变换法分别求解含三阶色散效应和不考虑三阶色散情况下的光孤子非线性薛定谔（NLS）方程,通过数值求解发现三阶色散效应会使孤子对脉冲发生单边振荡,并在振荡侧逐级产生次脉冲。讨论孤子对的两束孤子脉冲之间的振幅比与相位差对传输的影响,发现在不考虑三阶色散的情况下,振幅比与相位差均对孤子对的传输有显著影响,在考虑三阶色散效应时,只有相位差对孤子对的传输产生影响,并可以导致脉冲能量转移。     

亚皮秒啁啾孤子在凸形色散与线性色散平坦光纤中的传输特性比较

提出采用凸形色散平坦光纤(DFF-CVDP)传输亚皮秒啁啾孤子,利用分步傅里叶方法数值研究了亚皮秒啁啾孤子在DFF-CVDP中的传输特性,并与在线性色散平坦光纤(DFF-LDP)中的传输特性做了比较。结果表明,孤子脉冲在上述两种光纤中传输时,光纤损耗导致了孤子脉冲宽度随传输距离增加稍有展宽,脉冲方均根谱宽随传输距离增加逐渐减小。在DFF-LDP中,脉冲展宽更快,正啁啾对脉冲展宽的影响比负啁啾的影响更大,正啁啾对应的方均根光谱比其他情况下的宽得多。啁啾脉冲时域宽度随传输距离增加出现了衰减振荡,振荡周期和振幅随啁啾参量|C|的增加而增大。光孤子脉冲在两种光纤中传输时域波形保持不变,仍具有孤子特性。在DFF-LDP中,3β使得脉冲光谱红移从而诱导了脉冲时延,负啁啾减弱了3β的作用,正啁啾加强了β3的影响。在DFF-CVDP中传输可以忽略3β的影响。     

基于增益诱导光纤激光器的实验研究及理论分析

利用非线性偏振旋转技术,实现了正色散掺铒光纤激光器的自启动锁模,产生了一种新型的增益诱导孤子脉冲输出.该类型脉冲的光谱近似为矩形,半高全宽光谱宽度可达19 nm以上,脉宽为皮秒量级.增益诱导孤子脉冲的形成是增益饱和、光谱滤波效应、腔内色散和各种非线性效应共同作用的结果.同时还分析了脉冲啁啾特性及峰值功率等参数.当抽运功率增加时,该激光器还可以实现双脉冲模式下运转. 关键词： 光纤激光器 增益诱导孤子 啁啾     

Significance of prechirping on long-haul path-averaged soliton impulse in re-circulating loop at 10 and 20 Gb/s with TOD

In this paper, we have investigated the performance of first- and second-order path-averaged soliton long-haul transmission link including the impact of third-order dispersion (TOD) at varied chirp. Here, the varied chirp is considered keeping in view the inadvertent frequency chirp imposed on all practical sources of short optical pulses. The propagation of strongly chirped pulses in loss-managed long-haul path-averaged soliton transmission network has been shown. The investigations reveal that in first-order (N=1) path-averaged soliton transmission link at 10 and 20 Gb/s, SPM effect on the rising and falling edges of a pulse results in spectral broadening for all values of induced chirp. On the contrary, spectral narrowing of the pulses is observed in second-order negatively chirped path-averaged soliton pulses. The effect of the nonlinearity changes from narrowing to broadening of pulses if the sign of the initial chirp is changed to positive. The results ascertain that the system is capable of transmitting a pulse up to the distance of 24,500 km at bit rates of 10 and 20 Gb/s. Investigations have been carried out by varying the chirp factor in the range −1 to 1 and −1 to 0.4] for 10 and 20 Gb/s, respectively, to demonstrate the robustness of the long-haul soliton link. The observations establish that the pulse width (full-width at half-maximum (FWHM)) remains within the optimal range even at the transmission distance of 24,500 km without and at discrete values of the chirp factor.     

Role of dispersion profile in controlling emission of dispersive waves by solitons in supercontinuum generation

We study the supercontinuum process in optical fibers numerically for a variety of dispersion profiles to investigate how a specific dispersion profile controls the emission of dispersive waves. We conclude that the number of zero-dispersion points in the dispersion profile of a fiber is an excellent predictor of the dispersive-wave peaks when it is pumped with femtosecond pulses in the anomalous dispersion regime. Our study reveals that two or more such peaks can form on the same side of the input wavelength in specially designed and practically achievable dispersion profiles. We show that dispersive waves are emitted even in the case of normal dispersion where soliton fission does not occur. We suggest that a phenomenon related to soliton spectral tunneling is responsible for this radiation. Distinct dispersive peaks may also appear when an optical pulse, launched in the normal dispersion region, later begins to propagate in the anomalous dispersion regime because of its spectral broadening. Several dispersion profiles are numerically employed to show how the soliton fission process creates non-solitonic radiation even under normal dispersion pumping. A time-domain picture clearly shows this radiation when the conventional phase matching condition is satisfied. We also propose a realistic photonic crystal fiber with a dispersion profile that supports dispersive-wave generation in the normal-dispersion region. Our study should prove useful for experiments designed to control the generation of blue light by launching femtosecond pulses into optical fibers.     

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。     

Enhanced Compression of Fundamental Solitons in Dispersion Decreasing Fibers with Negative Third-order Dispersion Ⅱ. Effects of Fiber Characteristics and Initial Soliton Width

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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.     

Simulative analysis of soliton-based DPSK transmission system

The effectiveness of the conventional dispersion compensation techniques: DCF, FBG and OPC to use with soliton transmission is presented. The frequency shifts of solitons induced by collisions between different channels in a soliton WDM system can be reduced by dispersion compensation. The reduction mechanism applied is the cancellation of the shifts generated in both normal and anomalous dispersion regimes. It is analyzed that phase jitter can be reduced by the use of midway spectral inversion.     

Enhanced Compression of Fundamental Solitons in Dispersion Decreasing Fibers with Negative Third-order Dispersion Ⅱ. Effects of Fiber Characteristics and Initial Soliton Width

Previous work have shown that the combined effects of negative third-order dispersion (TOD) and Raman self-scattering (RSS) can significantly enhance soliton compression in dispersion decreasing fibers (DDFs). In this paper, the effects of the negative TOD coefficient and the effective amplification of DDF′s on the performance of soliton compression are investigated. It is shown that for a given initial soliton width and a given effective amplification, there exists an optimum value of the negative TOD coefficient of the DDF at which the enhancement in soliton compression is maximum. It is also shown that the compression enhancement saturates when the effective amplification exceeds a certain value, which has been explained as a compromise between the higher-order effects induced increase of the ratio of input to output group-velocity dispersion coefficients of the DDF and the TOD induced non-adiabatic compression characteristics. The dependence of the compression enhancement on the initial soliton width have also be studied and the scheme is found works well for solitons with initial widths less than 3 ps.     

L-band polarization-controlled multiple dissipative solitons generation in a normal dispersion fiber ring laser

A polarization-controlled multiple dissipative solitons generation in a normal dispersion fiber ring laser operating in L-band is demonstrated. The fiber laser is passively mode-locked with nonlinear polarization rotation (NPR) technique. Depending on the rotations of the PCs, the number of the pulses circulating in the laser cavity can be tuned from 1 to 4. The experimental results suggest that the generation of multiple pulses is caused by the soliton shaping of dispersive waves induced by the variations of spectral filtering effect.