Propagation of Femtosecond Optical Solitons in Dispersion-flattened Fibers

１ＩｎｔｒｏｄｕｃｔｉｏｎＳｏｌｉｔｏｎｂａｓｅｄｏｐｔｉｃａｌｃｏｍｍｕｎｉｃａｔｉｏｎｓｙｓｔｅｍｓａｒｅａｔｒａｃｔｉｎｇｃｏｎｓｉｄｅｒａｂｌｅａｔｅｎｔｉｏｎｂｅｃａｕｓｅｏｆｔｈｅｉｒｐｏｔｅｎｔｉａｌｆｏｒｓｉｇｎｉｆｉｃａｎｔｌｙｉ...     

Characteristics of pulse evolution in mode-locked thulium-doped fiber laser

We have numerically investigated the characteristics of the pulse evolution in a passively mode-locked thulium-doped fiber laser with net anomalous cavity dispersion. For the fixed resonator configuration, single-, dual-, triple-, and quadruple-pulses are generated successively by enhancing the pump power or reducing the output ratio. The characteristics of the single or multiple pulses are investigated with various cavity lengths. The separation between the two coexisting pulses changes with the pump power due to the interaction between the soliton and the dispersive waves, and then the two randomly distributed pulses could finally evolve into a soliton pair with fixed separation. According to the results of the numerical simulation, the multiple pulses are found to be generated via pulse splitting and the pulse splitting threshold decreases with the increase of the cavity length.     

压缩平稳重调脉冲的色散渐减光纤的设计

文章根据平稳重调脉冲(SRP)在梳状光纤(CPF)结构中的压缩原理,对色散渐减光纤(DDF)的色散特性进行设计,结果发现该色散渐减光纤的色散特性呈线性递减.对于平稳重调脉冲其压缩比与功率比等于光纤始末两端二阶色散系数的比值.当色散渐减光纤的斜率足够小时,无啁啾基阶孤子可以近似为平稳重调脉冲,当色散渐减光纤的色散斜率较大时,无啁啾基阶孤子不能近似为平稳重调脉冲.当基阶孤子带有与光纤色散斜率成正比的线性啁啾时,脉冲的压缩比与功率比更接近于光纤始末两端二阶色散系数的比值.说明带有线性啁啾的基阶孤子比不带啁啾的基阶孤子更接近于平稳重调脉冲. 关键词： 平稳重调脉冲(SRP) 梳状光纤(CPF) 色散渐减光纤(DDF) 色散递减表达式     

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.     

数值模拟高阶色散和非线性对光孤子传输的影响

光孤子传输中的高阶色散以及高次非线性效应是光纤通讯发展的重要制约因素。从光孤子在光纤中的一般传输方程出发, 在较大的入纤功率的前提下, 综合考虑了高阶色散、五次非线性和损耗因素, 得到其具体传输方程, 并据此从理论上分析了高阶色散和非线性对光孤子传输性能的影响。本文采用分步傅里叶方法, 以MATLAB为实现工具, 实现高阶色散和非线性对光孤子传输影响的模拟计算, 并深入分析了高阶色散和非线性导致的孤子脉冲频移现象。计算结果表明: 在入射功率较大的时候, 高阶色散效应不可忽略。当五次非线性γ2>0时,孤子脉冲主峰发生微小频移; 而当五次非线性γ2<0时, 孤子脉冲主峰基座产生微小频移; 当高阶色散β3>0时频率出现红移, 而当β3<0时, 频率出现蓝移。     

Observation of antisymmetric dispersion-managed solitons in a mode-locked laser

We report experimental evidence of antisymmetric solitons in a mode-locked fiber laser with a strong dispersion map. A dispersion-managed soliton breathes as it traverses the dispersion map, and the antisymmetric dispersion-managed soliton can be considered a tightly bound soliton pair with pi phase difference between the component solitons. The antisymmetric soliton is observed only at particular values of the net cavity dispersion.     

Simulative demonstration of soliton pulse stability over the nonlinear regime in a birefringent optical fiber

In this paper, the results of numerical analysis are demonstrated for sech pulse (soliton) propagation in a birefringent optical fiber using computer modeling and simulation. Here, the initial pulse is polarized linearly and guided into the fiber at an angle of 45° to its polarization axes. The birefringence-induced time delay of 200 and 440 ps between X and Y polarization components has been reported at a fiber length of 631.72 km (10 soliton periods) by considering linear and nonlinear regimes, respectively. The Kerr nonlinearity, which stabilizes solitons against spreading due to GVD, also stabilizes them against splitting due to birefringence. A similar fact is true for the birefringent walk-off. Above a certain soliton order (N_th), the evolution scenario is qualitatively different and two orthogonally polarized components of the soliton move with a common group velocity despite their different modal indices or polarization mode dispersion (PMD) at a fiber length of 631.72 km (10 soliton periods) and 1264.344 km (20 soliton periods) over a nonlinear regime at θ≠45°. The physical effect responsible for this type of behavior is the cross-phase modulation (XPM) between the two polarization components.     

Soliton Transmission Research on using Dispersion Step Fiber Chain Instead of Soliton Fiber

ＳｏｌｉｔｏｎＴｒａｎｓｍｉｓｉｏｎＲｅｓｅａｒｃｈｏｎｕｓｉｎｇＤｉｓｐｅｒｓｉｏｎＳｔｅｐＦｉｂｅｒＣｈａｉｎＩｎｓｔｅａｄｏｆＳｏｌｉｔｏｎＦｉｂｅｒＹＵＪｉａｎｊｕｎＹＡＮＧＢｏｊｕｎ＋ＧＵＡＮＫｅｊｉａｎＹＡＮＧＱｉｍｉｎＺＨＡＮＧＸｉａ...     

Vector dissipative solitons in graphene mode locked fiber lasers

Vector soliton operation of erbium-doped fiber lasers mode locked with atomic layer graphene was experimentally investigated. Either the polarization rotation or polarization locked vector dissipative solitons were experimentally obtained in a dispersion-managed cavity fiber laser with large net cavity dispersion, while in the anomalous dispersion cavity fiber laser, the phase locked nonlinear Schrödinger equation (NLSE) solitons and induced NLSE soliton were experimentally observed. The vector soliton operation of the fiber lasers unambiguously confirms the polarization insensitive saturable absorption of the atomic layer graphene when the light is incident perpendicular to its 2-dimentional (2D) atomic layer.     

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。     

强双折射光纤中超短光脉冲压缩效应研究

研究了强双折射光纤中沿偏振主轴入射的超短光脉冲压缩效应。当考虑三阶色散效应时，三阶色散与光纤非线相互作用能增强一偏振光脉冲的压缩而抑制另一偏振光脉冲的压缩。正三阶和的强慢孤子压缩，负三阶色散增强快孤子压缩，三阶色散参量越大，脉冲压缩效果越明显。     

Universal soliton pattern formations in passively mode-locked fiber lasers

We investigate multiple-soliton pattern formations in a figure-of-eight passively mode-locked fiber laser. Operation in the anomalous dispersion regime with a double-clad fiber amplifier allows generation of up to several hundreds of solitons per round trip. We report the observation of remarkable soliton distributions: soliton gas, soliton liquid, soliton polycrystal, and soliton crystal, thus indicating the universality of such complexes.     

Soliton molecule in fiber laser

The soliton molecule is achieved in nonlinear polarization rotation fiber laser. The structure of soliton molecule is heterogeneous diatomic molecule. The soliton molecule originates from the splitting of the high energy soliton. The dips of the soliton molecule spectra show that there is the interaction between the constituents of the soliton molecule, resulting in that the constituents are in the bound state as a unit. The laser bias can change the fine structure of the soliton molecule, which can be observed in the autocorrelator and oscilloscope.     

光孤子在色散缓变光纤中传输时的等价增益

从准非线性Ｓｃｈｒ?ｄｉｎｇｅｒ（ＮＬＳ）方程出发，导出了色散缓变光纤中光孤子脉冲传输所满足的与常规光纤中含增益效应等价的ＮＬＳ方程，给出了该方程的微扰解析解和光孤子脉冲宽度演化表达式。对于阶跃型单模光纤，得到了光纤几何参数与增益系数之间的一般函数关系。最后采用数值模拟方法模拟了不同色散缓变光纤中光孤子脉冲传输特性，指出色散缓变光纤不仅能补偿光纤损耗对孤子脉冲的展宽效应，而且能压缩光孤子脉冲，因而预计它可能有较广泛的应用前景。 关键词：     

On the behaviour of dispersion-managed soliton from the perspective of its energy components

We investigate the behaviour of dispersion-managed (DM) soliton from its energy. Using the variational analysis, it is possible to represent the energy of the DM soliton as a combination of three components, respectively, one component for the average dispersion of the optical fiber, second component for the local dispersion of the dispersion map and the third component for the Hamiltonian of the anomalous fiber section. From the results of the numerical simulations, we show that the Hamiltonian component of the DM soliton energy plays a vital role in the determination of its stability.     

利用相位共轭与色散配置实现具有大占空比和大放大器间隔的长距离光孤子传输

在用光纤放大器补偿损耗的光纤传输线中，用负色散光纤与正色散光纤或色散补偿器件交叉配置，并使传输线中光纤的有效色散适当大于（与平均孤子对应的）理论值，同时在传输线中周期地使用相位共轭器，可以在把放大器间隔提高到与常规光纤通信相同的条件下有效地削弱孤子之间的互作用。本文对实现速率为２５Ｇｂｉｔ／ｓ、占空比为１／２、光放大器间隔为１００ｋｍ、传输距离大于６０００ｋｍ的光孤子传输作出了数值论证     

非均匀系统中非自治孤子的色散和非线性管理

基于包含自发拉曼散射和外电光调制效应的非自治非线性薛定谔方程,采用简单的变换方法,解析研究了三种非均匀系统中非自治孤子的管理和传输。结果发现,在非均匀的非线性渐增或色散渐减光纤系统中都存在精确的啁啾非自治孤子解,都可以实现孤子的放大和压缩,但具有不同的速度、频移和啁啾特性;而在非均匀的色散和非线性均渐减光纤系统中,可以支持无啁啾的非自治孤子,该孤子具有不变的脉宽和振幅以及振荡衰减的速度,孤子的频移仅由自发拉曼散射决定。同时,数值模拟结果进一步证实在三种非均匀管理系统中都可支持非自治孤子的传输。该研究结果为实际非均匀孤子管理系统中实现孤子的压缩和传输提供了理论依据。     

Soliton Rectangular Pulses and Bound States in a Dissipative System Modeled by the Variable-Coefficients Complex Cubic-Quintic Ginzburg-Landau Equation

The complex cubic-quintic Ginzburg-Landau equation(CQGLE) is a universal model for describing a dissipative system,especially fiber laser.The analytic one-soliton solution of the variable-coefficients CQGLE is calculated by a modified Hirota method.Then,phenomena of soliton pulses splitting and stable bound states of two solitons are investigated.Moreover,rectangular dissipative soliton pulses of the variable-coefficients CQGLE are realized and controlled effectively in the theoretical research for the first time,which breaks through energy limitation of soliton pulses and is expected to provide theoretical basis for preparation of high-energy soliton pulses in fiber lasers.     

实现20Gbit/s的OTDM孤子信号56km色散位移光纤的传输

在国内最先采用孤子的方式将8×2.5Gb/s的OTDM信号在色散位移光纤中传输了56.1km,对8×2.5Gb/s的OTDM进行解复用后进行了误码测量,系统功率代价为2.9dB.系统采用增益开关半导体激光器作光孤子源,高Q电滤波方式提取时钟,非线性光学环路镜解复用。孤子脉冲最大半宽度为20ps,传输光纤平均色散1.2ps/nm/km。     

Propagation of short soliton pulses through a parabolic index fiber with dispersion decreasing along length

A parabolic index dispersion decreasing fiber (DDF) has been designed and optimized to produce high capacity soliton communication system. Variation of different fiber parameters such as core radius, effective core area and GVD factor along the 25 km of DDF length has been carried out to optimize a best possible DDF which can sustain the propagation of fundamental soliton. The variation of non-linearity with length along with the conventional power and GVD factor variation has been included in the generalized non-linear Schrodinger equation (NLSE). This NLSE has been solved numerically by split step Fourier method for shorter pulse propagation, incorporating the term for third order dispersion and intrapulse Raman scattering. Stable soliton pulses in transmission system have been achieved by our simulation, when a correction factor due to Raman induced soliton mean frequency shift is incorporated to the GVD profile predicted by the fundamental soliton condition. The interaction of neighboring soliton pulse pair through the proposed fiber has also been studied.