Effects of initial frequency chirp on the linear propagation characteristics of the exponential optical pulse

In this paper, the linear propagation characteristics of the exponential optical pulse with initial linear and nonlinear frequency chirp are numerically studied in a single mode fibre for \be₂<0. It can be found that the temporal full width at half maximum and time-bandwidth product of exponential pulse monotonically increase with the increase of propagation distance and decrease with the increase of linear chirp C for C<0.5, go through an initial decreasing stage near \zeta=1, then increase with the increase of propagation distance and linear chirp C for C\geq0.5. The broadening of pulses with negative chirp is faster than that with positive chirp. The exponential pulse with linear chirp gradually evolves into a near-Gaussian pulse. The effect of nonlinear chirp on waveform of the pulse is much greater than that of linear chirp. The temporal waveform breaking of exponential pulse with nonlinear chirp is first observed in linear propagation. Furthermore, the expressions of the spectral width and time-bandwidth product of the exponential optical pulse with the frequency chirp are given by use of the numerical analysis method.     

电位移矢量仅与自由电荷有关的充要条件及其应用

利用矢量场的唯一性定理直接给出了电位移矢量仅与自由电荷有关的充要条件；阐明了一个很有用的结论。     

超高斯型光脉冲在零色散区传输特性的研究

根据超短脉冲在光纤中传输所遵从的高阶非线性薛定谔方程,采用分步傅里叶方法模拟了超高斯型超短脉冲在光纤中的传输演化.在零色散区对损耗、高阶色散、高阶非线性、啁啾等因素对光脉冲传输的影响进行分析并得出了一些结论:损耗对传输脉冲的形状影响比较小基本上可以忽略,对脉冲的幅度影响比较大.一阶孤子传输一段距离后稳定时的幅度和脉宽在传输时基本不变,是进行光孤子通信的理想载体,而高阶孤子在开始传输和传输过程中的幅度和脉宽变化较大.当这些因素共同作用时,对脉冲的传输特性有较大的影响.但通过合理的选择各个影响因素的参量,能得到一个比较适于信息传输的高阶孤子脉冲.这对通过提高入射光脉冲功率使光脉冲在光纤中形成高阶孤子来提高两光中继器之间的中继距离的研究有一定的参考意义.     

空间光孤子脉冲在平面光波导中的传输

分析研究了空间光孤子脉冲化后在反常群速色散的克尔非线性平面光波导中的传输特性和稳 定性.当空间光孤子脉冲的时间宽度等于某一临界值时，脉冲发生自陷，小于该值时，脉冲 发生扩散，大于该值时，脉冲发生塌陷.空间光孤子的阶数越高，这个临界值越小.当空间光 孤子脉冲的时间宽度等于某一特定值时，脉冲塌陷最快，与这个特定值相差越大，塌陷越慢 .空间光孤子的阶数越高，这个特定值越小.脉冲自陷后的峰值光强、时间和空间宽度与输入 时的值有明显的不同. 关键词： 脉冲自陷 脉冲塌陷 光孤子     

初始啁啾对双曲正割光脉冲线性传输特性的影响

采用分步傅里叶方法数值研究了初始线性啁啾和非线性啁啾双曲正割光脉冲在单模光纤反常色散区的线性传输特性，并与啁啾高斯脉冲的线性传输特性作了比较.给出了双曲正割光脉冲频谱宽度和时间带宽积随初始线性啁啾变化的表达式.结果表明，双曲正割脉冲在线性啁啾|C|>0.1时随传输距离的增加逐渐演化成近高斯型，在0≤|C|≤0.1时最后将演化为近双曲正割脉冲.|C|越小，脉冲时域波形越趋近双曲正割曲线.负啁啾对脉冲时域展宽的影响比正啁啾要大得多.当|C|≥0.5时，初始啁啾对双曲正割光脉冲展宽的影响比对高斯脉冲的影响更大.非线性啁啾双曲正割光脉冲在线性传输过程中会出现时域波形分裂现象，比具有相同啁啾的高斯脉冲时域波形分裂严重. 关键词： 频率啁啾 双曲正割光脉冲 线性传输 时域波形分裂     

在光纤零群速色散区传输的光孤子波

通过对超短光脉冲在单模光纤中传输方程的分析研究,给出了在零群速色散传输方程的亮,反波解。结果表明,超短光脉中在光纤的零群群速色散仍能以亮,暗孤波的形式传输,且不存在孤子自频移现象。     

光脉冲在标准单模光纤中演化形成孤子的实验研究

利用二次谐波频率分辨光学门脉冲分析仪从实验上分析研究了具有啁啾的10 GHz光脉冲在不同输入功率下演化形成孤子的规律和特点。实验发现:输入脉冲在光纤中传输3.5个色散长度时,其时间宽度、频率啁啾和时间带宽积都随着输入功率的增加而减小。当输入功率大于一阶孤子功率的理论值时,光脉冲能够演化形成孤子;脉冲在随后传输过程中其宽度基本保持不变,波形、频率啁啾和时间带宽积仍随着传输距离的变化而变化;输入功率越高,形成的一阶孤子脉冲的宽度越窄。当输入功率小于一阶孤子功率的理论值时,输出脉冲的时间宽度随着传输距离的增加而增加,频率啁啾随着传输距离的增加而减小,光脉冲不能演化形成孤子。     

一种四排短轴渐减椭圆空气孔阵列的单模单偏振光子晶体光纤

提出了一种新型的四排短轴渐减椭圆空气孔阵列的单模单偏振光子晶体光纤结构,并以完美匹配层为边界条件采用全矢量有限元方法研究了该光纤的各种特性及其各种参量随入射波长变化规律.研究表明,提出的光子晶体光纤结构是实现更宽带宽、色散平坦、单模单偏振运用的有效方案;在入射光波长为1.550μm时,单模单偏振光子晶体光纤的模式双折射...     

Effect of initial linear chirp on collision characteristics of two solitons in the birefringent fibre

The collision characteristics of the orthogonally polarized solitons with initial linear frequency chirp in the linear birefringent fibre for \beta ₂<0 are numerically studied. It is found that initial chirp changes the threshold value of solitons to form the bound-state in the birefringent fibre. The effect of initial positive chirp on the threshold value is more obvious than that of negative chirp. In the case of \delta = 0.7 and initial interval 2\tau₀ = 1.25, the two solitons are mutually bound for 0.2 \le C \le 1, and they do not form the bound-state for -1 \le C<0.2. Frequency shifts increase with the increase of chirp parameter C for -1 \le C<0.2, and have the oscillatory structure for C \ge 0.2. The effect of positive chirp on temporal FWHM is greater than that of negative chirp. The peak of temporal waveform oscillates with the propagation distance. The period and amplitude of the oscillation for the chirped case are greater than those for the unchirped case, and they vary with the increase of | C| . The peak of output temporal waveform can be controlled by changing the initial chirp.