【作者】 熊杰；

【导师】 罗斌；

【作者基本信息】 西南交通大学 ， 通信与信息系统， 2005， 博士

【摘要】 提高光纤通信系统传输容量主要有两个途径,第一,提高单信道的传输码率,随着码率提高,色散通过展宽脉冲而对系统性能产生的影响逐渐增强,通常采用色散管理(DM)降低线路平均色散减小这一影响;第二,在相同的带宽内安排尽可能多的信道,随着信道间距的减小,交叉相移调制(XPM)效应逐渐增强,劣化了系统性能。 本文工作围绕DM和XPM两方面展开,包括单信道DM系统中补偿光纤长度优化;单段线路以及多周期色散管理波分复用(WDM)系统中XPM所致的强度调制、相位调制;以抑制XPM为目的的DM线路优化;WDM系统内混频过程中损耗、自相位调制(SPM)、XPM作用下的调制不稳定性(MI),具体内容有: 对单信道传输系统,以后补偿DM线路为例采用数值法对补偿光纤长度进行了优化,发现后补偿DM系统中脉冲宽度变化规律为缓变包络先压窄、再展宽,脉宽最窄点的位置随补偿程度的增加而减小,最小脉宽随补偿程度的增加而增加;与单周期最大压缩补偿相比,补偿程度适当减小时能够在一定传输距离内有效减小脉冲展宽,随着脉冲峰值功率的提高,最优补偿长度将随之提高。 对于强度调制直接检测(IM-DD)系统,采用表征XPM所致强度调制的频域传递函数和时域强度调制率作为性能评价指标,研究了群速度色散(GVD)和泵浦波SPM作用下的XPM效应。首先,推导了单段、多段放大线路中表征XPM所致强度调制的频域传递函数,给出了任意泵浦条件下,探测信道输出端的时域波形、时域强度调制率计算方法。然后,分析了调制频率、光纤色散以及泵浦波SPM对XPM的影响。最后,以抑制DM线路中的XPM为目的,分析了补偿方式(前补偿或后补偿)及补偿光纤长度选择问题,发现最优补偿方式并非固定不变,补偿方式的选择同时受补偿光纤长度和传输距离(色散管理周期数目)的影响。 对于相干光通信系统,采用表征XPM所致相位调制的频域传递函数和时域相位调制率作为性能评价指标,研究了GVD作用下传输波形变化时的XPM效应。首先推导了单段、多段放大线路中GVD作用下传输波形变化时表征XPM所致相位调制的频域传递函数,给出了探测信道时域相移、时域相位调制率计算方法。随后,分析了调制频率、传输距离、光纤色散等对XPM的影响。最后,以减小DM线路中XPM所致相移为目的,对各种补偿方案(欠补偿、完全补偿、过补偿、前补偿及后补偿)进行了比较,结果表明对更多还原

【Abstract】 There are two main methods to improve transmission capability of optical communication systems. One is to increase bit rate in single channel. With the increase of bit rate, the impact that dispersion impose on pulses by widening pulses width strengthens gradually. Usually dispersion management (DM) is adopted to weaken the impact by reducing the average dispersion of transmission line. The other is to arrange more channels in same bandwidth. With the reducing of channel spacing, cross-phase modulation (XPM) strengthens gradually and the systems performance is degraded.This work focused on DM and XPM, which included the length optimization of compensation fiber in single channel DM systems, the intensity modulation and phase modulation induced by XPM in single segment fiber and multi-periods DM wavelength division multiplexing (WDM) systems, the DM system optimization for restraining XPM, the modulation instability (MI) in frequency-mixing process under the effect of loss, self-phase modulation (SPM) and XPM in WDM systems.With the example of single channel post-compensation DM systems, the length of compensation fiber was optimized by simulation. It is found that the slowly-varying-envelope narrows firstly, broaden and then. With the enhancement of compensation degree, the distance corresponding to the narrowest pulse width reduces and the least pulse width increases. It is found that the widened pulse width could be decreased effectively by reducing compensation degree comparing with single period and the max compression. The optimized compensation length increases with the enhancement of maximum power.For intensity modulation-direct detection (IM-DD) systems, the XPM under the effect of group velocity dispersion (GVD) and SPM were investigated by using the frequency domain transfer function (FDTF) and time domain intensity modulation index to evaluate systems performance. First, the FDTFs corresponding to XPM were derived in single segment and multi-segments amplification systems. The methods to calculate the time domain wave shape and time domain intensity modulation index were given when arbitrary pump signalswere inputted. Then, the effects of modulation frequency, fiber dispersion and SPM of pump signals on XPM were analysed. At last, compensation schemes (pre-compensation or post-compensation) and the length choice for compensation fiber were discussed for restraining XPM in DM systems. It is found that the optimized compensation scheme is variable. The choice of compensation scheme is affected by the length of compensation fiber, transmission distance or the number of DM periods.For coherent optical systems, the XPM were investigated by using the FDTF and time domain phase modulation index to evaluate systems performance when the wave shape of propagated pulses was changed by GVD. First, the FDTFs in single segment and multi-segments amplification systems were derived when the wave shape of propagated pulses was changed by GVD. The methods to calculate time domain phase shift and time domain phase modulation index in probe channel were given. Then, the effect of modulation frequency, transmission distance and fiber dispersion on XPM were analysed. At last, the different dispersion compensation schemes (under-compensation, full-compensation, over-compensation, pre-compensation, post-compensation) were compared for restraining the phase shift induced by XPM. The results show that the post-compensation scheme is superior to pre-compensation scheme. The average dispersion should be away from zero average dispersion when we choose the length of compensation fiber.For the MI under the effect of XPM in WDM systems, focusing on the two carried frequencies and sideband frequencies generated in the frequency-mixing process, the calculation method of MI gain in frequency-mixing process under the effect of loss, GVD, SPM and XPM was given by couple mode method. The expressions of MI gain caused by SPM or XPM of carried frequencies were given when one phase matched perfectly and others mismatched seriously. The maxima of gain are independent of GVD when the MI is caused by SPM or XPM mainly. The maxima of gain at different sidebands are equal when MI is caused by XPM. Only when the frequency shift is large enough, there is the MI gain after considering the fiber loss. The frequency shift corresponding to the maximal gain caused by SPM decreases after considering the fiber loss. With the increase of transmission distance, the MI gain peak induced by SPM closes up tocarries frequencies.The theory models and the results in this paper are useful for analysis and design of long distance and high capacity IM-DD or coherent detection WDM systems.更多还原