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.     

双折射对孤子传输的影响及其相互作用控制

利用对称分步傅里叶法,数值研究了双折射光纤中孤子的传输特性,分析了孤子脉冲的入射偏振角为30°时两偏振分量群速度失配对孤子传输产生的影响。结果表明,光纤的双折射大小影响着脉冲峰值对时间的漂移程度,双折射越大,峰值漂移越多。如果光纤的双折射具有随机性,峰值漂移被修正,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,合成强度没有太大的变化,孤子能够稳定的传输。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。     

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.     

PCF中群速度失配和高阶色散对孤子自俘获的影响

基于分步傅里叶方法,仿真研究了光子晶体光纤(PCF)在反常色散区的群速度失配因子δ、高阶色散(主要是三阶色散)对孤子自俘获效应的影响.研究结果表明:随着群速度失配δ的增大,两偏振分量的平均振幅差值也增大,孤子自俘获效应变差;三阶色散量增大时,孤子自俘获效应变差.因此,只有选择合适的特性参数值才可以得到比较好的孤子自俘获效应,此特点可用于实现光开关等光信号处理功能器件.     

光纤零色散波长点附近光孤子传输特征的理论分析

本文利用约化摄动重整化方法研究了光纤零色散波长点附近光孤子传输的特征。研究结果表明,光纤零色散波长点附近,光孤子仍然存在并能够稳定地传输,由于光纤损耗和三阶色散效应的影响,光孤子的振幅按指数规律衰减,标准光孤子分裂成孤子和非孤子两部分。     

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。     

五阶非线性效应下源啁啾飞秒孤子间相互作用

对五阶非线性效应下源啁啾飞秒孤子间的相互作用进行了数值研究.结果表明,五阶非线性效应影响下,源啁啾参数值较小时,两孤子经过一段传输距离后发生碰撞,然后一直处于排斥状态;随着源啁啾参数值增大,两孤子传输时碰撞次数增多;当源啁啾参数值增大到一定值以后,两孤子产生裂变,且源啁啾参数值越大孤子间裂变越严重.最后,采用不等振幅法对五阶非线性效应影响下源啁啾飞秒孤子间的相互作用进行了有效的抑制.     

高双折射双芯光子晶体光纤偏振分束器

设计了一种基于双折射效应的新型矩形纤芯光子晶体光纤偏振分束器,通过在矩形晶格结构的光子晶体光纤的每个纤芯中引入一对椭圆来增加结构的双折射。应用全矢量有限元法（FEM）分析了双芯光子晶体光纤中结构参数对双折射和耦合长度特性的影响,数值模拟了该偏振分束器的性能。结果表明:增大椭圆率可以在增大结构的双折射的同时减小耦合长度,并且该分束器在工作波长为1.55 m、传输长度为282 m 的光纤中能够实现偏振状态的隔离,消光比达到最小值-45.42 dB,并且在1.507~1.596 m、带宽为89 nm 的范围内消光比小于-10 dB。     

熊猫光纤热双折射效应光纤偏振控制器研究

根据熊猫光纤热双折射效应原理.通过电热控制的方法实验研究其热双折射效应,提出并实验演示了基于熊猫光纤热双折射效应的光纤偏振控制器.研究了熊猫光纤热双折射效应的温度灵敏度和电热控的特点.将两段熊猫光纤按偏振轴相互偏离一定角度熔接后,两段熊猫光纤的电热控制将分别在邦加球上形成相交并互相成一定夹角的两个截交线圆,组合两段熊猫光纤的电热控制可实现偏振态在邦加球上的部分覆盖.根据熊猫光纤热双折射效应的特点,提出并实验演示了由三段熊猫光纤组成的电热控光纤偏振控制器,它可在实验上实现任意偏振态的扫描控制.     

色散位移光纤中Kerr系数的随机扰动对光孤子传输的影响

从描述色散位移光纤中Kerr系数随机扰动影响下皮秒光孤子的修正非线性薛定谔 (NLS)方程出发 ,利用对称分步Fourier方法 ,数值研究了光孤子在Kerr系数随机扰动情况下的传输演化特性。结果表明 ,Kerr系数的随机扰动使单孤子幅值随传输距离产生了微小波动 ;对两孤子传输的影响主要表现在孤子间相互作用被加强。研究结果还表明 ,相邻孤子的不等振幅注入法能够有效抑制孤子间相互作用     

三阶色散情况下光纤中类明孤子演化特性的研究

本文从含修正的非线性薛定谔方程出发,采用变分法,导出了三阶色散情况下光纤中类明孤子参数随传输距离的演化方程组;在此基础上,求出了振幅与脉宽、频率与啁啾及中心位置、脉宽与啁啾之间的三个约束关系和脉宽演化的解析解;讨论了三阶色散对类明孤子演化特性的影响。     

波分复用系统中偏振模色散特性的研究

推导了双折射光纤中两个波长的光波所满足的耦合非线性薛定谔方程。建立了研究两信道波分复用(WDM)系统中偏振模色散效应的模型。基于这一模型,在考虑偏振模色散情况下,数值模拟了在两信道WDM系统中光信号的传输变化,并且分析了在此系统中偏振模色散的影响     

Short pulse generation by higher order soliton-effect compression:effects of optical fiber characteristics

The effects of optical fiber characteristics on higher order soliton-effect pulse compression are investigated. We show that, for the compression of pulses with widths in the range of a few picoseconds or less, stimulated Raman scattering and third order dispersion result in severe degradation of the optimum compression ratio F_opt, while self-steepening has negligible effect. The initial pulse width dependence and the group velocity dispersion dependence of F_opt are investigated, leading to the identification of regimes that maximize F_opt and minimize the compressed pulse width. The effects of stimulated Raman scattering and third order dispersion on the quality of the compressed pulses are also investigated     

Dual Orthogonal Polarization States in an Active Mode-Locked Birefringent Fiber Ring Laser

We report the generation of dual amplitude pulses in an active mode-locked fiber laser within a birefringent cavity. Different to normal mode-locked pulses with identical amplitude and polarization state, and pulses polarized on both x- and y-axes simultaneously exist in the output pulse train. The two orthogonal pulse sequences have different amplitudes and lase at different wavelengths. Dual wavelengths are the result of red shift and blue shift of the x- and y-polarization states of the generated pulses, respectively, due to the detuning phenomena. Locking to individual x- or y-polarized pulse is also obtained by adjusting polarization controllers     

Novel procedure to determine statistical functions of impulsive noise

One of the problems found when measuring impulsive noise is to distinguish this kind of noise from Gaussian noise. Usually, a threshold level is used to make the difference. The problem is that a high threshold level will miss low amplitude pulses, while a low level will include Gaussian noise samples as being impulsive noise. In this paper, results of a novel radio UHF impulsive noise measurement procedure are presented. This work exhibits the peculiarity that data was taken in both horizontal and vertical polarizations simultaneously. One polarization is used to determine the presence of impulsive noise so analysis can be performed in the other polarization considering this circumstance. Measurements were made in four different locations on UHF TV channels around 800 MHz with a bandwidth of 10 MHz, demodulating the in-phase and quadrature phase components in each polarization. When environments are constituted by varied and scattered impulsive sources, horizontal and vertical polarizations show similar statistical behavior. However, horizontal and vertical emissions may be different when a single source is individually measured. The conditional amplitude probability density function (pdf) and conditional amplitude cumulative distribution function (cdf) found for the amplitude in all the locations lead to the conclusion that the variable that best fits the results is a lognormal one.     

具有高阶耦合色散系数双芯非线性光纤耦合器开关的数值分析

基于耦合非线性薛定谔方程(NLSE),利用分裂步长傅里叶方法(SSFM),研究了具有高阶耦合色散系数时,双芯非线性光纤耦合器中的传输和开关特性.模型中,一阶耦合色散系数的存在类似于群速度失配,二阶耦合色散系数类似于群速度色散,并且会对另一个纤芯中的信号产生线性互调制.研究表明当一阶耦合色散系数较小时,光脉冲仍能在二纤芯之间周期性耦合传输,并且表现出良好的开关特性,当一阶耦合色散系数增大时,脉冲耦合传输的周期性和陡峭的开关特性遭到破坏,光脉冲在传输中发生分裂;二阶耦合色散系数使耦合器的耦合长度减短,开关阈值功率增加,开关特性也变得更加陡峭.     

单模光纤中四阶色散导致的调制不稳定性

利用修正的非线性Ｓｃｈｒｏｄｉｎｇｅｒ方程研究了单模光纤在最小群速度色散波长附近的调制不稳定性。从理论上给出了一个新的由光纤四阶色散导致的调制不稳定区域，新区域的最大调制增长率和调制范围与光中的初始入射功率和四阶色散有关，光纤自陆峭效应和Ｒａｍａｎ延勺时调制不稳定区域的最大调制增长率和调制范围都有影响，自肖效应对新区域的影响较大且存在一个决定新区域出现与否的阈值。Ｒａｍａｎ延迟效应对调制不稳定必的     

Pre-threshold conductance and polarization effects in amorphous semiconductor switches

It is shown that the conductance and threshold parameters of threshold switches depend on the manner in which switching systems are addressed. Slow voltage ramps lead to internal polarization; fast square pulses do not. The polarization processes influence all switching operations performed sequentially; their room-temperature relaxation time is of the order of several milliseconds. The observations are interpreted on the basis of a space charge model involving injected carriers, subsequently trapped.     

First-order PMD compensation in nonlinearly dispersive opticalcommunication systems via transmission over the principal states ofpolarization

Soliton propagation in the presence of polarization mode dispersion (PMD) is studied with an analytical approach. It is shown that there exist two peculiar initial states of polarization that may prevent the soliton to undergo shape distortions. These states coincide with the states that, in the absence of chromatic dispersion and nonlinearity, are usually referred to as principal states of polarization. This fact is used to show that it is possible to improve the performance of an optical transmission system operating in the presence of chromatic dispersion, PMD and Kerr nonlinearity by coupling the input pulses to one of the principal states of polarization     

提高激光雷达测距精度的最佳信号门限比

为了提高脉冲激光雷达的测距精度,研究了光束在空域为高斯光束、时域为钟型脉冲的激光雷达在恒电压幅度鉴别模式下,回波信号幅度变化和宽度变化对测距精度的影响。证明在一定范围内,由回波幅度变化所造成的测距误差与由回波脉宽变化引起的测距误差,随鉴别电平的取值不同,呈现出相反的变化趋势,即最佳信号门限比的存在,并导出了相应的计算公式。通过改变接收信号强度,对不同信噪比、不同信号门限比条件下大量测距实验结果进行了分析,验证了最佳信号门限比的存在。在一定的实验条件下,最佳信号门限比的取值在1.8附近,实验结果与理论计算吻合良好。这一研究结果为不同应用条件下,激光雷达鉴别电平的合理选取提供了依据。