超短光脉冲在有源三芯非线性光纤耦合器中开关和传输特性的数值分析

基于耦合非线性薛定谔方程(CNLSEs),利用分裂步长傅里叶方法(SSFM),研究了超短光脉冲在有源三芯非线性光纤耦合器中的传输和开关特性.重点分析了在一阶色散耦合系数和二阶色散耦合系数的影响下,线性增益系数和有限增益带宽对脉冲传输和开关特性的影响.研究表明,线性增益系数能增大开关陡峭性、降低开关临界能量、提高开关效率;虽然有限增益带宽使耦合器开关特性变差,但是它不仅能显著抑制由线性增益系数引起的脉冲压缩和放大,而且还能有效抑制由一阶色散耦合系数引起的脉冲展宽和分离以及由二阶色散耦合系数引起脉冲高频振荡,使光脉冲在三纤芯间呈现出类似无源光纤耦合器那样的周期性耦合传输特性.     

非对称非线性定向耦合器开关特性研究

利用拉格朗日变分法原理,分析了非对称非线性定向耦合器的开关特性.研究表明:增大第一纤芯的相速度能够降 低开关的阈值功率,但开关的陡峭性变差,且当相位失配量增大到一定程度,输入低功率脉冲时,光脉冲的部分能量将一直保 持在直通纤芯臂内不能耦合到第二纤芯.增大第一纤芯的有效模场面积将导致开关的阈值增大.同时,当两纤芯都为反常...     

高阶色散下随入纤功率变化的不稳定性增益谱

为了探讨不同入纤功率下高阶色散对交叉相位调制不稳定性增益谱的影响,从光纤中包含高阶色散的耦合非线性薛定谔方程出发,采用线性稳定性分析法,分二阶、四阶色散系数同号、异号和二阶色散系数为0等几种情形,计算了双光束的交叉相位调制不稳定性增益谱随入纤光功率的变化规律,并对各种谱特性的产生机制作了分析。结果表明,当二阶、四阶色散系数同号时,随着入纤功率的增大,增益谱由开始的两个分离谱区逐渐变宽并合成1个谱区;当二阶、四阶色散系数异号和二阶色散系数为0时,增益谱只有靠近零点的第1谱区,且谱宽和谱峰随着入纤功率的增大而增大。此研究对高重复率的超短光脉冲串的产生有一定的理论指导意义。     

光纤定向耦合器的开关特性研究

基于耦合非线性薛定谔(NLS)方程组,利用分步傅里叶法(SSFM),研究了二阶色散长度与线性耦合系数的乘积LDκ、三阶色散长度与线性耦合系数的乘积L′Dκ以及模间色散(IMD)对双芯非线性光纤定向耦合器开关特性的影响。研究表明,在光纤正常色散区,当入射功率大于阈值功率时,从波导1到波导2有明显的能量转移,耦合器的开关性能差;而在光纤反常色散区,当LDκ1时,非线性定向耦合器(NLDC)能够表现出良好的开关特性。且阈值功率随着LDκ的增大而减小。当|IMD|≤0.01,IMD对NLDC开关特性的影响可以忽略。当|IMD|=0.2,且LDκ的值较小时,在入射功率大于阈值功率的条件下,IMD对开关特性的影响不明显;而在入射功率小于阈值功率时,耦合器的开关特性下降。此外,三阶色散(TOD)效应对NLDC的影响通常可以忽略。     

光子晶体光纤中非线性传输的数值研究

数值模拟了飞秒激光脉冲在光子晶体光纤中的非线性传输过程,详细计算分析了自相位调制（SPM）、脉冲内拉曼散射（ISRS）、自陡峭（SS）以及群速度色散（GVD）、三阶色散（TOD）、四阶色散(FOD)对脉冲传输和频谱的影响。结果表明,在反常色散区,脉冲内拉曼散射以及三阶、四阶色散对频谱的展宽和脉冲的平滑都有着重要作用;而自陡峭是使高阶孤子分量产生分裂衰变,对光谱的不对称展宽有一定影响。     

负折射介质中高阶非线性效应所致啁啾的研究

利用分步傅里叶法对负折射介质中的广义非线性薛定谔方程进行数值模拟,进而分别得到自相位调制、赝五阶非线性、自陡峭、二阶非线性色散所致啁啾及各项非线性所致总啁啾的演变图.从啁啾上分析了负折射介质中各项非线性效应在脉冲传输时的作用,结果表明,负折射介质中,自陡系数取值的正负可控使脉冲中心位置可向前后沿偏移;在正常色散区,赝五阶非线性系数为负时加速脉冲的展宽,二阶非线性色散项系数取正时使脉冲展宽,取负时使脉冲变窄.     

五阶非线性和高阶色散作用下超高斯脉冲的传输特性

从非线性薛定愕方程出发,用变分法得出了描述锐度因子为不同自然数的超高斯脉冲在光纤色散(高阶和二阶)和非线性(三阶和五阶)作用下传输的微分方程组,用龙格-库塔算法对微分方程组进行数值求解,结果表明对于给定的较小的光纤色散和非线性系数,都存在特定的三阶和五阶非线性系数使非线性有效地对高阶和二阶色散给脉冲传输造成的展宽影响加以补偿,此时超高斯脉冲在光纤以近似保形的状态稳定传输。当色散系数与非线性系数之比太大时脉冲将被无限展宽。     

五阶非线性下双脉冲相移和啁啾的解析研究

从光纤中扩展的耦合非线性薛定谔方程组出发,在同时考虑五阶非线性、脉冲间群速度失配和初始时延的情况下,忽略光纤色散效应,导出了载频不同的两高斯脉冲由于交叉相位调制所致的非线性相移和频率啁啾的解析公式.结果表明,与只有三阶非线性的情况相比,三五阶非线性的共同存在会使脉冲间群速度失配,且初始时延对脉冲的非线性相移和频率啁啾会产生更为综合和复杂的影响.该研究在光开关器件和频率转换等方面有一定的指导意义.     

双芯光纤中孤子传输与耦合特性研究

利用自伴算符方法,通过耦合非线性薛定格方程分析了双芯光纤中孤子的传输与耦合特性。研究结果表明：孤子脉冲在两纤芯间的耦合特性与注入的孤子振幅有密切关系,耦合特性表现为周期性、非完全周期性和完全非周期性的能量变换;孤子脉冲在两纤芯间的传输特性与注入的两孤子间相对相位有密切关系。     

分步傅里叶法研究负折射介质中超短脉冲的传输

采用分步傅里叶法来研究负折射介质中超短脉冲的传输特性,分析了超短脉冲在负折射介质中传输时所体现出来的新特点.结果表明,在正常色散区,二阶非线性色散系数为负时使脉冲变窄,而且它对脉冲影响的程度是随着传输距离不断变化的,影响越来越小;赝五阶非线性系数为负时使脉冲展宽,但与二阶非线性色散项相比影响较小;而自陡系数取值的可正、可负出现了使脉冲在传输过程中其中心位置前后沿均可偏移的现象.     

Effects of Second-Order Coupling Coefficient Dispersion on Short-Pulse Propagation and Switching in an Active Two-Core Nonlinear Fiber Coupler

The propagation and switching of short pulses in an active two-core fiber nonlinear directional coupler have been investigated theoretically by using the split-step Fourier method. The analysis highlights the effects of the second-order coupling coefficient dispersion, the linear gain coefficient, and the finite-gain bandwidth on the switching and propagation of short pulses. The research indicates that the linear gain can sharpen the switching characteristic and reduce considerably the switching threshold power, as well as significantly increase the switching efficiency with the influences of the second-order coupling coefficient dispersion. However, both the second-order coupling coefficient dispersion and the finite-gain bandwidth degrade the switching characteristics. In addition, the finite-gain bandwidth of linear gain not only suppresses significantly the pulse compression and amplification caused by the linear gain coefficient, but also suppresses effectively the frequent pulse fluctuation on pulse propagation induced by the second-order coupling coefficient dispersion; consequently, as in the case of the passive fiber coupler, optical pulses tend to restore periodical coupling propagation in active two-core fiber coupler.      

Nonlinear propagation and self-switching of ultrashort opticalpulses in fiber nonlinear directional couplers: the normal dispersionregime

The propagation of short optical pulses in a nonlinear directional coupler operating in the normal dispersion regime is investigated. The specific example of a birefringent periodically rocked fiber filter where coupling occurs between the two orthogonally polarized modes that are aligned with the birefringence axes of the fiber is considered. In the simulations, a bell-shaped input pulse is injected into one polarization mode: for different input peak powers, the energy present in the same mode at the output of a coupler, which is one or two coupling lengths long, is calculated. The nonlinear temporal broadening, due to the combined effect of group velocity dispersion and self-phase modulation, sets a fundamental lower limit to the time width of the input pulses. When pulses shorter than this critical value are used, the power-dependent energy switching characteristics of a device one coupling length long gets substantially spoiled. Effects related to the finite spectral bandwidth of the fiber filter are discussed. Numerical simulations are compared to recent experimental results on the self-switching of picosecond pulses in the visible (615 nm) with a birefringent rocking fiber     

Nonlinear optical pulse coupling dynamics

The pulse coupling dynamics in a nonlinear directional coupler (NLDC) is analyzed by using the new normalized coupled nonlinear Schro/spl uml/dinger equations. The operation of an NLDC can be divided into three regions according to L/sub D//spl kappa/: Region 1 (L/sub D//spl kappa//spl les/1), Region 2 (L/sub D//spl kappa/>50), and Region 3 (1相似文献   

The calculation of switching power of symmetric and asymmetric nonlinear directional couplers with variable coupling coefficient

It is proposed that the switching power of symmetric one-coupling-length nonlinear directional couplers (NLDC) with variable coupling coefficient (VCC) can be calculated as the weighted average of the local critical power of the coupler. Further, it is shown that the switching characteristics of a one-coupling-length VCC NLDC are determined mainly by the first half of the coupler and the switching power of an asymmetric VCC NLDC can be calculated as the weighted average of the local critical power over the first half of the coupler. Both symmetric and asymmetric examples are presented.     

Switching dynamics of short optical pulses in a nonlineardirectional coupler

It has been shown recently that the propagation of short optical pulses in a nonlinear directional coupler consisting of two parallel waveguides or fibers should be described more generally by a pair of coupled nonlinear equations that take into account the dispersion properties of the coupling coefficient. In this paper, we use the Fourier series analysis method to solve these equations, and study the effects of a dispersive coupling coefficient on the switching dynamics of short optical pulses in a nonlinear directional coupler. We demonstrate, with numerical examples, that a dispersive coupling coefficient could cause significant pulse distortion and affect the threshold switching intensity. The effects of introducing frequency chirps in the input pulses are also discussed     

飞秒弧子脉冲在非线性定向耦合器中的传输控制研究

本文研究了超短脉冲在非线性定向耦合器中的传输控制。在飞秒级超短脉冲情况下 ,三阶色散效应变得很重要 ,需对在耦合器中的皮秒级脉冲传输控制方程进行修正。用对称分步傅里叶变换方法进行数值模拟分析 ,结果表明通过选择不同强度的正交极化同步控制脉冲 ,可对在NLDC中超短信号弧子脉冲的传输方向进行控制     

Time-resolved switching characteristic of the nonlinear directionalcoupler under consideration of susceptibility dispersion

Two new forms of nonlinear coupled mode theory are presented which allow a quantitatively correct calculation of the temporal and spatial field evolution in a nonlinear coupler. The resultant set of coupled equations for the Fourier transforms of the pulse envelopes of the basis functions are numerically solved for representative coupling and excitation conditions. The approach permits the treatment of the power and time dependent switching characteristics of ultrashort pulses by accounting for the frequency dependence of the susceptibilities and coupling integrals. The results show that switching efficiency is low in the positive dispersion region due to pulse breakup. The pulse breakup can also be observed in the negative dispersion region, with pulses representing higher order solitons having a peak power on the order of the continuous-wave switching power     

基于非线性放大环镜的全光开关特性研究

采用掺铒光纤放大器(EDFA)和高非线性色散位移光纤(HNL—DSF)组成非线性放大环镜(NALM)，利用掺铒光纤放大器的高增益系数和高非线性色散位移光纤的光学克尔效应构造全光开关，实现脉冲整形和消除干扰噪声。采用分布傅里叶法分析了高非线性色散位移光纤的群速度色散(GVD)对非线性放大环镜开关特性的影响，讨论了掺铒光纤放大器的增益系数、增益饱和特性以及耦合器的耦合比等因素的影响，研究了入射光为高斯脉冲的情况下，非线性放大环镜与入射光信号强度相关的放大滤波特性。通过优化非线性放大环镜的各项参数，可以在实现高开关效率的同时，降低对开关功率的要求，对峰值功率低于1mW的超短脉冲进行Tbit／s量级的开关操作，从而适用于超高速大容量光通信系统中。     

高阶色散和非线性效应下三阶孤子对传输的研究

高阶色散及高阶非线性效应是制约光孤子稳定传输的重要因素。基于光孤子传输的非线性薛定谔方程,综合考虑三阶色散和五阶非线性的影响,采用分步傅里叶算法,数值研究了三阶孤子对间的相互作用。结果表明：三阶色散导致三阶孤子对无规则地裂变,裂变后的光脉冲形状发生畸变,脉冲中心位置出现偏移;考虑负五阶非线性作用后,在一定程度上抑制了孤子裂变,但是光脉冲在传播过程中伴有能量转移。而正五阶非线性作用使三阶孤子对传输图形进一步恶化。适当地选取负五阶非线性参数值,可以完全消除三阶孤子对的裂变和相互作用,改善了脉冲中心位置的线性偏移。