随机双折射光纤中孤子的相互作用与控制

利用对称分步傅里叶法,数值模拟了光孤子在随机双折射光纤中的传输特性,研究了孤子间的相互作用及其非线性增益控制.结果表明,随机双折射使得孤子传输的两偏振分量脉冲强度会随着传输距离有强弱不规则的变化,但是两偏振分量的强度变化互相补充,合成孤子强度能够稳定地传输;随机双折射也增强了孤子间相互作用,非线性增益可以有效地抑制随机双折射对孤子传输相互作用的影响,使得原本会产生交叠走离的相邻孤子传输不偏离原来的时间槽,实现了对偏振模色散良好的控制作用.     

双折射光纤中三阶色散对孤子稳定性的影响

本文研究了单模光纤中双折射效应和高阶色菜和效应对弧 子传输稳定性影响。研究结果表明：线性双折射所导致的两偏振孤子分离的振幅阈值三阶色散的影响而增大,如果增大脉冲 振幅的阈值以上,那么两个垂直方向的偏振孤子将锁定在一起传输。     

随机双折射光纤中基于孤子俘获效应的偏振模色散的抑制

利用分步傅里叶方法数值解耦合非线性薛定谔方程组,研究了孤子脉冲和高斯脉冲在随机双折射光纤中的传输特性.研究结果表明:当脉冲的入射功率大于一定阈值时,两偏振分量能相互捕捉并以相同速度传输.这种现象就是俘获效应,它能有效地抑制偏振模色散.     

偏振模色散对飞秒孤子脉冲传输的影响

以Maxwell电磁场理论为基础,在综合考虑了高阶色散、高阶非线性、自相位调制、交叉相位调制、自变陡、脉冲内喇曼散射以及偏振模色散(PMD)等因素的基础上,推导了飞秒孤子脉冲在双折射光纤中传输的耦合非线性薛定谔方程(NLSE)。利用分步傅立叶方法对该方程进行了数值计算,通过对该系统的仿真,研究分析了PMD对飞秒孤子传输的影响。结果发现当PMD参量Dp≤0．1 ps／km1／2时,输出脉冲宽度和峰值功率相对于初始脉冲几乎不变,随着Dp值的增大,脉宽增加,峰值功率降低。当Dp≥1．0 ps／km1／2时,脉冲显著展宽,孤子的两偏振分量发生严重走离。     

偏振模色散对飞秒孤子脉冲传输的影响

以Maxwell电磁场理论为基础，在综合考虑了高阶色散、高阶菲线性、自相位调制、交叉相位调制、自变陡、脉冲内喇曼散射以及偏振模色散（PMD）等因素的基础上，推导了飞秒孤子脉冲在双折射光纤中传输的耦合非线性薛定谔方程（NLSE）。利用分步傅立叶方法对该方程进行了数值计算，通过对该系统的仿真，研究分析了PMD对飞秒孤子传输的影响。结果发现当PMD参量Dp≤0．1ps／km^1／2时，输出脉冲宽度和峰值功率相对于初始脉冲几乎不变，随着Dp值的增大，脉宽增加，峰值功率降低．当Dp≥1．0ps／km^1／2时，脉冲显著展宽，孤子的两偏振分量发生严重走离。     

利用光脉冲传输特性抑制偏振模色散

基于双折射光纤中光脉冲传输方程,详细分析了二阶色散、自相位调制以及交叉相位调制在光脉冲传输过程中引起的啁啾。分析结果显示:通过合理选取入射功率,二阶色散引起的啁啾与自相位调制引起的啁啾在脉冲中心附近可以相互抵消,从而使脉冲展宽最小;交叉相位调制产生的两偏振分量的啁啾引起的频移,可使两偏振分量间产生互束缚,利用这种现象可以抑制偏振模色散。     

利用光脉冲传输特性抑制偏振模色散

基于双折射光纤中光脉冲传输方程，详细分析了二阶色散、自相位调制以及交叉相位调制在光脉冲传输过程中引起的啁啾。分析结果显示：通过合理选取入射功率，二阶色散引起的啁啾与自相位调制引起的啁啾在脉冲中心附近可以相互抵消，从而使脉冲展宽最小；交叉相位调制产生的两偏振分量的啁啾引起的频移，可使两偏振分量间产生互束缚，利用这种现象可以抑制偏振模色散。     

阶跃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,研究了非线性双折射色散阶跃光纤(SWDF)中两相近频率的激光脉冲,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2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,在反常非线性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,当输入功率和波长差(或频率差)一定时,增益谱随传输距离变化保持形态不变.     

色散管理传输系统中克尔效应对偏振模色散的补偿研究

光纤的随机双折射效应可导致脉冲无规展宽即偏振模色散(PMD)。在零路径色散管理孤子传输系统中，二阶色散和三阶色散效应均被完全补偿，克尔效应成为一种有害因素会使脉冲变窄，但是当光纤的随机双折射被考虑时，克尔效应正好与PMD相互抵消，使光脉冲准稳定传输，不同的光纤偏振模色散参数分别对应不同的最佳系统功率。此外，如果考虑不同偏振方向的损耗差异，则即使在最佳匹配条件下，微小的偏振损耗差异也可产生很大的脉宽波动。因此，偏振相关损耗是影响脉冲传输质量的相当重要的因素，不论在理论计算还是在工程设计中都应当认真考虑。     

强双折射光纤中三阶色散对DGD的影响

依据强双折射光纤中两垂直偏振分量所满足的非线性耦合模方程,研究了三阶色散对偏振分量间的时延差的影响。结果表明,当二阶色散、三阶色散同时存在时,三阶色散可以减小时延差;当只有三阶色散时,除了产生较大时延差外,还会在两个偏振脉冲的前后沿产生较大的色散波。     

Propagation of solitons in fibers with randomly varyingbirefringence: effects of soliton transmission control

Propagation of solitons in fibers with randomly varying birefringence is studied with and without including the effect of soliton transmission control. A simple expression for the decay of soliton energy due to the birefringence is derived, which will be useful in predicting soliton-pulse broadening in randomly birefringent fibers with their polarization-mode dispersion parameter specified. It is also shown that transmission control of solitons effectively removes dispersive radiations generated by the birefringence     

Pulse-train uniformity in optical fiber lasers passivelymode-locked by nonlinear polarization rotation

The generation of uniform soliton pulse trains by additive pulse mode locking has been experimentally demonstrated in a birefringent fiber laser with a passive polarizer. Numerical simulations of pulse propagation around such a fiber loop are presented which reveal that this mode-locking scheme does not result in strictly uniform pulse trains. Rather, the train of output pulses exhibits periodic fluctuations in intensity and polarization. A model for the pulse dynamics is developed which shows that these fluctuations depend on the strength of the fiber birefringence and the alignment of the polarizer with the fast- and slow-polarization axes of the fiber. It is also shown that increased uniformity of pulse trains is achieved with near alignment of the polarizer with the slow axis of the birefringence     

Time Jitters Caused by Randomly Varying Birefringence in Soliton Transmission System

Soliton propagation in fiber with randomly varying birefringence is studied by using self-companying operator method. It is shown that randomly varying birefringence leads to time jitters increasing with transmission distance, and disrupts the stability of soliton transmission. The fluctuation of time jitters is stochastic, and nonlinear gain is introduced to remove the influence.     

Application of the Manakov-PMD equation to studies of signalpropagation in optical fibers with randomly varying birefringence

We report on our investigations of the Manakov-polarization mode dispersion (PMD) equation which can be used to model both nonreturn-to-zero (NRZ) and soliton signal propagation in optical fibers with randomly varying birefringence. We review the derivation of the Manakov-PMD equation from the coupled nonlinear Schrodinger equation, and we discuss the physical meaning of its terms. We discuss our numerical approach for solving this equation, and we apply this approach to both NRZ and soliton propagation, We show by comparison with the coupled nonlinear Schrodinger equation, integrated with steps that are short enough to follow the detailed polarization evolution, that our approach is orders of magnitude faster with no loss of accuracy. Finally, we compare our approach to the widely used coarse-step method and demonstrate that the coarse-step method is both efficient and valid     

Simultaneous generation of wavelength tunable two-coloredfemtosecond soliton pulses using optical fibers

Wavelength tunable two-colored femtosecond (fs) soliton pulse generation is proposed and demonstrated for the first time, using passively mode-locked fs fiber laser and polarization maintaining fibers. The wavelengths of the two soliton pulses can be changed arbitrarily by varying the power and polarization direction of the fiber-input pulse. Ideal two colored soliton pulses in which the pulsewidths are about 200 fs are generated in the wavelength region of 1.56-1.70 μm for 110-m fiber. The generated pulses are almost transform-limited ones     

Nonlinear optical loop mirror based on standard communication fiber

We numerically analyze the effectiveness of a nonlinear optical loop mirror (NOLM) based on standard communication fiber with randomly varying birefringence for demultiplexing streams of picosecond pulses at 100 GHz. A broad switching window of about three pulse full-width at half maximum (FWHM) can be obtained. The device performance is defined by the pulse duration, the dispersion of the fiber, and the fiber length. We show that imperfect averaging of the randomly varying birefringence causes amplitude fluctuations on the NOLM transmission curve. We also show that the Raman self-frequency shift does not affect the NOLM switching characteristics at picosecond pulse durations     

Complete characterization of terahertz pulse trains generated fromnonlinear processes in optical fibers

The measurement technique of frequency-resolved optical gating (FROG) is used to characterize the intensity and phase of terahertz pulse trains generated from nonlinear and dispersive interactions in optical fibers. We show that existing FROG retrieval algorithms are easily adapted to allow the retrieval of periodic pulse characteristics and, using synthetic pulse trains generated from numerical simulations, we demonstrate how FROG can differentiate between periodic pulse trains with fundamentally different intensity and phase characteristics, yet qualitatively similar autocorrelation functions and spectra. Experimental results are presented for the FROG characterization of a 0.3-THz sinusoidal beat signal from a dual wavelength laser source, a 2.5-THz train of dark solitons generated in a high-birefringence fiber, and a 0.6-THz bright polarization domain wall soliton train generated in an ultra-low birefringence fiber. These results are shown to be in good agreement with nonlinear Schrodinger equation simulations     

Compact system of wavelength-tunable femtosecond soliton pulsegeneration using optical fibers

Using passively mode-locked femtosecond (fs) fiber laser and polarization maintaining fibers, the compact system of wavelength-tunable femtosecond (fs) fundamental soliton pulse generation is realized. The monocolored soliton pulse, not multicolored ones, with the ideal sech² shape is generated, and its wavelength can be linearly shifted by varying merely the fiber-input power in the wide wavelength region of 1.56-1.78 μm for a 75-m fiber. The soliton pulses of less than 200 fs are generated with the high conversion efficiency of 75%-85%. This system can be widely used as a portable and practical wavelength-tunable fs optical pulse sources