GVD compensation schemes with considering PMD

Three group velocity dispersion (GVD) compensation schemes, i.e., the post-compensation, pre-compensation and hybrid-compensation schemes, are discussed with considering polarization mode dispersion (PMD). In the 10- and 40-Gbit/s non-return-zero (NRZ) on-off-key (OOK) systems, three physical factors, Kerr effect, GVD and PMD are considered. The numerical results show that, when the impact of PMD is taken into account, the GVD pre-compensation scheme performs best with more than 1 dB better of average eye-opening penalty (EOP) when input power is up to 10 dBm in the 10-Gbit/s system. However the GVD post-compensation scheme performs best for the case of 40 Gbit/s with input power less than 13 dBm, and GVD pre-compensation will be better if the input power increased beyond this range. The results are different from those already reported under the assumption that the impact of PMD is neglected. Therefore, the research in this paper provide a different insight into the system optimization when PMD, Kerr e     

PMD effect on pulse shapes and power penalty in optical communication systems

We present an analytical expression relating the output state of polarization and the first-order polarization mode dispersion (PMD) vector in terms of the angle of precession of the output state of polarization around the PMD vector. We derive, incorporating for the first time this angle of precession, a general relation to study the effect of first-order PMD on pulses of arbitrary shapes, and expressions for pulse shape, pulse broadening and power penalty taking into account both PMD and chromatic dispersion. Measured experiment results are presented for NRZ, RZ, NRZ-DPSK, and RZ-DPSK modulation formats.     

高速传输系统中高阶PMD的影响

研究由于偏振模色散(PMD)引起的时域脉冲响应从传输矩阵的角度分析了包含各阶与频率相关的差分相时延(DPD)、主偏振态(PSP)对脉冲波形的影响,并通过仿真结果验证理论的有效性同时,也分析了PMD对系统带来的眼图代价,对40Gb/s系统做出了预测.     

40 Gb/s差分相移键控格式抗偏振模色散的性能研究

研究了40Gb/s非归零或归零格式下,差分相移键控和开关键控信号对一阶偏振模色散的影响.比较分析了不同偏振模色散影响下的各种调制格式的眼开度.结果表明:使用非归零和归零格式,在一阶偏振模色散情况下,差分相移键控信号均比开关键控信号有更高的眼开度;与归零差分相移键控格式相比,非归零差分相移键控格式受偏振模色散影响眼开度要小;对于给定的比特率,载波抑制归零差分相移键控格式比归零差分相移键控格式有更好的抗偏振模色散能力.     

Origin and System Effects of Polarization Mode Dispersion in Chirped Bragg Gratings

Polarization mode dispersion of chirped Bragg gratings is analyzed in terms of key birefringence phenomena and impact on telecommunication systems performance. The influence on polarization mode dispersion (PMD) of fiber birefringence, grating chromatic dispersion, and ripples of the group delay curve is pointed out. Polarization mode dispersion influence on systems performance is investigated by numerical simulations and transmission experiments at 10 Gbit/s. The deterministic nature of Bragg gratings PMD determines a moderate, upper-limited system penalty for a transmission line employing a single compensating device. However, in the case of broadband components, a non-negligible PMD penalty may be observed due to the difficulty of controlling accurately the group delay linearity.     

Origin and System Effects of Polarization Mode Dispersion in Chirped Bragg Gratings

Polarization mode dispersion of chirped Bragg gratings is analyzed in terms of key birefringence phenomena and impact on telecommunication systems performance. The influence on polarization mode dispersion (PMD) of fiber birefringence, grating chromatic dispersion, and ripples of the group delay curve is pointed out. Polarization mode dispersion influence on systems performance is investigated by numerical simulations and transmission experiments at 10 Gbit/s. The deterministic nature of Bragg gratings PMD determines a moderate, upper-limited system penalty for a transmission line employing a single compensating device. However, in the case of broadband components, a non-negligible PMD penalty may be observed due to the difficulty of controlling accurately the group delay linearity.     

高速光纤通信系统中抑制偏振模色散的新机制

重点研究了偏振模色散、群速度色散、自相位调制三者之间在高速光纤通信系统中的相互作用，从时域角度分析脉冲的演变，从频域角度分析频谱的变化，提出一定条件下，啁啾、色散、自相位调制可以部分补偿偏振模色散的思想。通过对40Gbit／s系统进行偏振模色散、群速度色散和自相位调制共同作用的仿真，从统计意义上验证了它们之间的相互影响，并找到最佳传输方案，对系统设计提供了参考。     

Bit-pattern-dependent polarization rotation in first-order PMD-compensated WDM systems

We demonstrate both numerically and experimentally that the phase-change due to fiber nonlinearities induces a bit-pattern-dependent rotation of the state-of-polarization which translates to uncertainty in the principal states of polarization. This effect severely limits the performance of the first-order PMD post-compensation and suggests the use of in-line compensators. Our simulation shows that fiber nonlinearities cause significant distortion (more than 4-dBm Q-penalty after 600-km transmission at 10 Gbit/s) after first-order PMD compensation. For optical powers as low as 3 dBm/channel in systems where PMD is not uniformly distributed along the transmission link, first-order PMD compensation may be ineffective.     

偏振效应损伤的光通信系统失效概率估算

采用多重重要抽样方法,研究了受偏振模式色散和偏振相关损耗损伤的10 Gbit/s光通信系统的功率代价和失效概率.仿真结果表明,光滤波器对功率代价有重要影响.采用法布里-珀罗滤波器的系统比采用四阶高斯型滤波器的系统有更好的性能表现;发现功率代价通常随着啁啾因子的增大而增大,但当啁啾因子为0.5左右时,系统性能达到最好.仿真结果也表明,即使偏振模式色散和偏振相关损耗同时存在,DPSK系统比OOK系统有更强的PMD和PDL耐受性.     

40Gb/s差分相移键控格式抗偏振模色散的性能研究

研究了40Gb／s非归零或归零格式下,差分相移键控和开关键控信号对一阶偏振模色散的影响．比较分析了不同偏振模色散影响下的各种调制格式的眼开度．结果表明：使用非归零和归零格式,在一阶偏振模色散情况下,差分相移键控信号均比开关键控信号有更高的眼开度;与归零差分相移键控格式相比,非归零差分相移键控格式受偏振模色散影响眼开度要小;对于给定的比特率,载波抑制归零差分相移键控格式比归零差分相移键控格式有更好的抗偏振模色散能力．     

Optical all-pass filters for polarization mode dispersion compensation

Polarization mode dispersion (PMD) compensation is addressed by decomposition of a fiber's Jones matrix into amplitude and phase responses, which are then compensated for separately. Cubic and higher-order phase compensation substantially reduce the cumulative probability at a given system penalty over first-order PMD compensation, as demonstrated for a 40-Gbit/s non-return-to-zero signal and a fiber PMD with a differential group delay of 20 ps (rms). Single-stage all-pass filters provide tunable compensation that is comparable to that obtained with a variable-delay line, and multistage all-pass filters are well suited for higher-order phase compensation.     

Comparison of soliton robustness with respect to polarization-mode dispersion with first-order polarization-mode dispersion compensated linear systems

Soliton robustness to polarization-mode dispersion (PMD) is compared, both analytically and numerically, with that of linear pulses that use first-order PMD compensation. It is found that soliton robustness to PMD is comparable with first-order PMD compensation and in some cases is even better. The effects of soliton control methods on soliton robustness to PMD were also investigated, and it was found that soliton control methods can significantly improve the soliton's robustness to PMD, particularly for long-distance systems.     

光纤偏振模色散对信号偏振度的影响

采用一种简化的线路传输模型，详细讨论了在高速光纤通信系统中，线路偏振模色散（PMD ），尤其是二阶PMD、输入信号偏振态等对信号偏振度（DOP）的影响，并指出以信号DOP做 反馈控制信号适合于一阶PMD优化补偿系统，但在较大二阶PMD的影响下，将增加控制算法的 复杂性，使系统可能陷入局部最优解. 关键词： 信号偏振度 偏振模色散 信号偏振态     

Three-chip differential phase-shift keying maximum likelihood sequence estimation for chromatic-dispersion and polarization-mode-dispersion compensation

We propose a novel three-chip differential phase-shift keying (DPSK) maximum likelihood sequence estimation (MLSE) for chromatic-dispersion (CD) and first-order polarization-mode-dispersion (PMD) compensation to extend the transmission reach of the DPSK signal. Such a technique searches the most probable path through the trellis for DPSK data sequence estimation by exploiting the phase difference between not only the adjacent optical bits but also the bits that are one bit slot apart. The proposed scheme significantly outperforms conventional two-chip DPSK MLSE in CD and PMD compensation. We show that the proposed three-chip DPSK MLSE can enhance the CD tolerance of 10 Gbit/s DPSK signal to 2.5 times of that by using two-chip DPSK MLSE and can bound the penalty for 100 ps differential group delay by 1.4 dB.     

40 Gb/s光时分复用系统中两级偏振模色散自适应补偿实验研究

偏振模色散效应严重制约着长距离高速光纤通信的发展,偏振模色散的自适应补偿成为光通信领域研究的焦点。利用两阶段偏振模色散补偿器,采用6个自由度的粒子群优化算法(PSO),通过在线监测搜索光纤链路信号的偏振度极值作为反馈控制信息,在40Gb／s归零码高速光纤传输链路中成功实现了ms量级的偏振模色散自适应补偿。补偿前后采用庞加莱球法测量光纤链路中偏振模色散量,测量结果表明在信号中心波长1560．5nm处,差分群时延补偿前后测量值分别为21ps和1．3ps,而二阶偏振模色散补偿前后测量值分别为266ps^2和43．5ps^2。补偿后实验链路中的一阶和二阶的偏振模色散同时得到不同程度的补偿,并且系统的总的功率代价在误码率为10^-9时小于1dB。     

Power penalty of cascaded Bragg gratings in the presence of PMD and PDL

Considering the presence of birefringence in Bragg gratings, the spectral polarization mode dispersion (PMD) and polarization dependent loss (PDL) induced power penalty of eye opening is examined for a network with cascaded Bragg gratings. It is shown that when the birefringence in the grating is less than 10⁻⁵, the induced power penalty is less than 0.1 dB for a network with up to 30 cascaded Bragg gratings. However, when the grating birefringence is on the order of 10⁻⁴, the induced power penalty can be as high as 5.6 dB for a network with 14 cascaded Bragg gratings.     

Impacts of polarization mode dispersion on the pulse-width with considering initial pulse chirp and fiber GVD

The impacts of polarization mode dispersion (PMD) on the pulse-width in linear systems have been investigated. The analytical solutions, including the effects of initial frequency chirp and group velocity dispersion (GVD), are derived. Analyses show that the pulse broadening effects induced by the second-order PMD depend on GVD and chirp parameter, which are different from those induced by the first-order PMD. An initially chirped Gaussian pulse is taken as an example, upon which analytical solutions of rms pulse-width are derived before and after the first-order PMD compensation. The first-order PMD compensator is also evaluated based on these solutions. The results show that the pulse broadening effects will be resisted efficiently by choosing appropriate GVD and chirp parameter; in general, the post-transmission compensation method will be less efficient than the PSP-transmission method.     

普通单模光纤传输系统的光纤光栅色散补偿研究

通过系统分析光纤光栅的耦合模理论 ,探索、优化光纤光栅的制作过程 ,研制了满足ITU T建议波长的优质光纤光栅。用双透镜和扫描移动平台结合相位掩膜板研制的光纤光栅分别成功实现了 4× 10Gb/s 4 0 0km和4× 10Gb/s 80 0km普通单模光纤传输系统的色散补偿 ,功率代价均小于 2dB ,且最佳功率代价为负值。同时对4× 10Gb/s 80 0km普通单模光纤传输系统的偏振模色散实施长时间的监测 ,系统偏振模色散小于 10 ps,提出了发展 10Gb/s的光通信系统更符合目前我国国情的见解。     

Numerical Modeling of PMD

A procedure for evaluating system performance considering all orders of polarization mode dispersion (PMD) is presented. The method provides engineering rules for computing system penalty introduced by PMD. Computer simulation of PMD induced penalty indicates that for generating a realistic system budget, effect of higher order PMD in presence of chromatic dispersion is essential. Considering all of these penalties, in order to obtain a system-reach of 3200 km at 40 Gb/s, a fiber PMD of less than 0.04 ps/km^1/2 is required when at the signal wavelength chromatic dispersion is 0. In presence of 18 ps/nm chromatic dispersion for the same system reach this PMD value reduces to about 0.02 ps/km^1/2.     

Analytical theory for pulse broadening induced by all-order polarization mode dispersion combined with frequency chirp and group-velocity dispersion

We derive an analytical expression for the expected root-mean-square (rms) pulse broadening with considering the combined effects of all-order polarization mode dispersion (PMD), group velocity dispersion (GVD) and frequency chirp. It is shown that two commonly used first-order PMD compensators lose their efficiency quickly with chirp parameter increasing if GVD is ignored. When GVD is added, prechirp technique is helpful for the enhancement of PMD tolerance for both uncompensated case and first-order compensators when GVD and PMD coefficient satisfy some special relationship.