啁啾FBG和DCF对16×10Gb/s系统进行色散补偿的性能研究

对负色散光纤法和啁啾光纤光栅法实现色散补偿的两种方案进行了模拟研究 ,结论是 :(1 )对各信道完全色散补偿的前提下 ,入纤光功率较小时 ,啁啾光纤光栅色散补偿系统误码性能较好 ;入纤光功率较高时 ,用负色散补偿光纤进行色散补偿效果更好 ;(2 )适当的欠补偿比完全补偿效果好 ,入纤光功率一定时 ,用啁啾光纤光栅比用负色散补偿光纤进行欠补偿的效果好     

利用后置补偿法对10-Gbit/s长距离波分复用光纤传输系统进行色散均衡

通过系统仿真,对以常规单模光纤和色散补偿光纤(SMF+DCF)组成的16×10-Gb/s WDM色散补偿系统进行了分析,调制器啁啾为0,激光器静态线宽为5MHz.结果表明:(1)对于数百公里的传输距离,以DCF进行在线补偿就可以使各个信息达到较好的色散补偿效果(16×10-Gb/s,400km,眼图代价差别小于0.5dB);(2)由于SPM在SMF光纤中对脉冲的压缩效应,每一信道应保持略微偏正的残留色散量;(3)对于上千公里的传输距离,仅以DCF进行在线补偿无法同时均衡所有信道的色散(16×10-Gb/s, 1200km,眼图代价差别大于0.85dB).为此,本文以SMF或DCF在系统接收端再次对各信道逐个进行色散补偿(后置色散补偿),达到了良好的效果(16×10-Gb/s, 1200km, 眼图代价差别小于0.3dB).     

光脉冲展宽的解析公式在高速WDM系统设计中的应用

给出了光脉冲在光纤群速度色散和自相位调制效应的共同作用下，均方奶宽度沿传播距离变化的近似解析公式，并重点讨论其在高速波分复用光纤通信系统设计中的应用。解析公式不仅能用于估计信道功率、光纤色散等参数的容限范围，还可为系统色散补偿或色散管理的优化设计提供指导。     

利用中点谱反转实现2.5Gb/s直接调制信号的200km常规单模光纤传输

报道了２．５Ｇｂ／ｓ直接调制光信号的２００公里常规单模光纤传输实验，系统中采用了基于色散位移光纤中四波混频效应扣点谱反转技术以补偿光纤色散的影响。     

基于线性啁啾光纤光栅色散补偿的2500km-10Gbps无电中继传输系统

全部利用线性啁啾光纤布拉格光栅(CBG)作色散补偿模块,在G.652光纤上实现2500km-10Gbps的超长距离无电中继传输系统。在2060km处,功率代价~2dBm(NRZ码,BER:10-12,PRBS:1023-1);在2530km处,较大功率代价下实现无误码传输,远超过相同条件下用色散补偿光纤(DCF)作色散补偿模块的传输系统的无误码传输距离。     

在DCF光纤中放大的背向自发拉曼散射的增益特性

光脉冲沿色散补偿光纤（DCF）传输会产生背向自发拉曼散射，当入纤激光功率大于阈值时，出现放大的背向自发拉曼散射现象。实验发现，反斯托克斯（ASR）和斯托克斯（SR）自身脉冲光纤拉曼放大的阈值泵浦峰值脉冲功率是18．2W和14．5W．当入纤激光功率为52W时，背向SR和ASR散射的增益分别为12dB和7dB。放大的反斯托克斯和斯托克斯背向自发拉曼散射时域曲线上的阈值时间位置随激发功率的增大而前移并具有规律性。     

清华大学采用中点谱反转(MSSI)技术实现2.5Gb/s直接调制信号的200公里常规单模光纤传输实验

清华大学电子工程系307主题课题最近利用色散位移光纤的四波混频效应实现了光谱反转,成功地进行了2.5Gb/s直接调制信号的200公里常规单模光纤传输实验.信号光源采用经过2.5Gb/s伪随机码直接调制的DFB激光器,它在不加和补偿措施的情况下经过100公里常规单模光纤传输时的功率代价为1.8dB.     

抑制等信道间距陆上干线光纤通信系统中光纤色散和四波混频效应的新方案

提出了一种用以克服等信道间距划分、波分复用（ＷＤＭ）＋掺饵光纤放大器（ＥＤＦＡ）陆上光纤通信系统中光纤色散和四波混频（ＦＷＭ）效应的新方案。采用１５５０ｎｍ处色散为－２．８９ｐｓ／ｋｍ／ｎｍ的小色散单模光纤（ｓｍａｌｌ－ｄｉｓｐｅｒｓｉｏｎｓｉｎｇｌｅ－ｍｏｄｅ－ｆｉｂｅｒ，ＳＤＳＭＦ）可避免严重的ＦＷＭ效应，同时利用ＩＴＵ－ＴＧ．６５２非色散位移光纤（ｎｏｎ－ｄｉｓｐｅｒｓｉｏｎ－ｓｈｉｆｔｅｄｆｉｂｅｒ，ＮＤＳＦ），在ＥＤＦＡ整个带宽范围内（１５３０～１５７０ｎｍ）补偿ＳＤＳＭＦ引入的负色散。采用此方案，一个１０路×１０Ｇｂ／ｓ、１０级ＥＤＦＡ级联的等信道间距（１ｎｍ）光纤通信系统，经近千公里的光纤传输后，ＦＷＭ和色散引入的恶化量将分别小于１ｄＢ。     

色散补偿型分布式光纤喇曼放大器的实验研究

在后向抽运和前向抽运方式下,采用光纤喇曼激光器作为抽运源,对S波段色散补偿型光纤喇曼放大器(FRA)进行了实验研究。在增益和噪声特性方面,后向抽运方式优于前向抽运方式。在后向抽运时,测量了5kmDCF-50kmG652光纤色散补偿型分布式FRA,分布式FRA和分立式FRA等三种FRA增益和噪声光谱特性,色散补偿型分布式FRA的增益和噪声特性均优于分布式FRA和分立式FRA。在后向抽运方式下,5kmDCF-50kmG652光纤色散补偿型分布式FRA的抽运功率增大时,其增益增大,噪声指数减小。在抽运功率为1.0W时,当信号功率为0dBm时,最大开关增益为21.4dB,增益光谱大于10dB的带宽超过50nm,噪声指数小于-0.05dB。在同样抽运条件下,色散补偿型FRA的增益与小信号功率无关。     

三层外空气孔对光子晶体光纤非线性和色散的影响

在以1550nm为中心的宽带波长范围内设计了一种宽带低非线性色散补偿光子晶体光纤,采用矢量光束传输法数值模拟了包层中空气孔层数、空气孔直径和空气孔节距对于其色散和非线性特性的影响.计算结果表明,内六层空气孔对于其色散与非线性特性有较强影响.通过优化调节第四到六层空气孔的直径和空气孔节距,设计了在以1550 nm为中心的100 nm带宽波长范围内对相当于自身长度190倍的普通单模传输光纤进行色散补偿的光子晶体光纤(色散补偿偏移率保持在0.5%以内),在此宽带波长范围内保持非线性系数低于3 W-1·km-1.     

Bismuth-based Brillouin/erbium fiber laser

A multi-wavelength Brillouin/erbium-doped fiber laser (BEFL) operating in the 1573 nm region is proposed and demonstrated. The system employs both linear and nonlinear gain from a bismuth-based erbium-doped fiber (Bi-EDF) approximately 215 cm long and a single mode fiber (SMF) of various lengths to generate an optical comb with a spacing of approximately 0.089 nm. Two 3 dB couplers were used to form a looping arm in the system in order to produce cascaded Brillouin Stokes waves as internal feedback for multi-wavelength operation. A stable output laser comb with 10 lines at more than ??13 dBm was obtained with 4.85 dBm Brillouin pump power and two 140 mW pumps at 1480 nm. The 1480 nm pumps' power and SMF length have a significant effect on the number of wavelengths and on the output power of the generated wavelength comb.     

采用DFB＋MZ调制器组件为光源的10Gb／s100kmG.652光纤传输实验研究

报道了运用ＤＦＢ－ＬＤ与Ｍ－Ｚ调制器单片集成组件为光源实现１０Ｇｂ／ｓ１００ｋｍ常规单模光张的传输实验。实验表明,采用光源预啁啾技术可延长系统的传输距离。在误码率ＢＥＲ＝１０＾－１０时,传输后的功率代价为１．１ｄＢ,接收灵敏度为－１６．５ｄＢｍ。这一结果达到了国外同类实验的水平。     

Coded-orthogonal frequency division multiplexing in hybrid optical networks

Future Internet should be able to support a wide range of services containing large amount of multimedia over different network types at a high speed. The future optical networks will therefore be hybrid, composed of different single-mode fibre (SMF), multi-mode fibre (MMF) and free-space optical (FSO) links. In these networks, novel modulation and coding techniques are needed that are capable of dealing with different channel impairments, be it in SMF, MMF or FSO links. The authors propose a coded-modulation scheme suitable for use in hybrid FSO - fibre-optics networks. The proposed scheme is based on polarization-multiplexing and coded - orthogonal frequency division multiplexing (OFDM) with large girth quasi-cyclic low-density parity-check (LDPC) codes as channel codes. The proposed scheme is able to simultaneously deal with atmospheric turbulence, chromatic dispersion and polarisation mode dispersion (PMD). With a proper design for 16-quadrature amplitude modulation (QAM)-based polarisation-multiplexed coded-OFDM, the aggregate data rate of 100 Gb/s can be achieved for OFDM signal bandwidth of only 12.5 GHz, which represents a scheme compatible with 100 Gb/s per wavelength channel transmission and 100 Gb/s Ethernet.     

Characterisation of a parallel optical all pass filter for chromatic dispersion equalisation in 10 Gb/s system

The chromatic dispersion (CD) that occurs in single mode fibres (SMFs) is an important issue that needs to be addressed in long-haul optical communication links. The effect of CD is pulse spreading which in turn leads to inter-symbol interference, thus resulting in the deterioration of the bit error rate (BER) performance of the system. An alternative CD compensation technique that utilises a parallel optical all pass filter (p-OAPF) is presented, where the p-OAPF design is based on the inverse phase response of the SMF. The p-OAPF is based on a class of all-pass filter. Simulation results of the proposed technique show an increase in the repeater-less length of a point-to-point optical communication system by up to three and four times using a non-return-to-zero data format with a rectangular and Gaussian pulse shape, respectively, at error-free condition (BER < 10~ ). The results also show that the p-OAPF is robust in performing dispersion equalisation at a wide range of SMF lengths to attain error-free communication.     

Effect of self-phase-modulation on dispersion compensated absolute polar duty cycle division multiplexing transmission

The effect of self-phase modulation (SPM) on 40 Gb/s absolute polar duty cycle division multiplexing (AP-DCDM) is investigated and reported. The study includes the influence of launched power, number of channels and dispersion compensation method. Dispersion post-compensation and combination of dispersion pre- and post-compensation are used to manage the transmission links. At high powers, SPM degrades the pulse recompression process and provides an upper bound on the AP-DCDM transmitted pulse energy. It is demonstrated that the 40 Gb/s AP-DCDM system shows a 4.1 dB improvement and less than 1 dB penalty in terms of SPM tolerance in comparison to 40 Gb/s 4-ary and on off-keying (OOK) systems, respectively. The SPM effect is stronger in the 100 post-compensated link than that in the combination of pre- and post-compensated links. Dispersion pre-compensation of 18 22 is found as the optimum range of pre-compensation ratio for AP-DCDM system, which makes optimisation of the launched power possible.     

Efficient compensation of chromatic dispersion and nonlinearities using logarithmic digital backward propagation in N-channel DWDM 1.12Tbit/s DP-QPSK transmission

We propose and numerically investigate the logarithmic step-size distribution for implementing an efficient digital backward propagation (DBP) algorithm using the split-step Fourier method (SSFM). DBP is implemented in N-channel dual-polarization quadrature-phase-shift-keying (DP-QPSK) transmission over 2000 km standard single-mode fiber (SMF) with no in-line optical dispersion compensation. This algorithm is compared with the constant step-size modified DBP (M-SSFM) algorithm in terms of efficiency, complexity and computational time. Furthermore, we investigate the same-capacity and same-bandwidth transmission systems with 14 Gbaud (GBd), 28?GBd and 56?GBd per-channel rates. The logarithmic step-size based DBP algorithm depicts efficient mitigation of chromatic dispersion (CD) and nonlinear (NL) impairment. The benefit of the logarithmic step-size is the reduced complexity and computational time for higher baud rates.     

Supercontinuum generation from a sub-megahertz repetition rate femtosecond pulses based on nonlinear polarization rotation technique

A means of supercontinuum (SC) generation is proposed and demonstrated, using femtosecond mode-locked pulses with sub-megahertz repetition rate based on the nonlinear polarization rotation technique. Total cavity length is approximately 522?m, which includes an additional 500?m single mode fiber (SMF) and the fundamental repetition rate obtained is 404.5?kHz. The mode-locked spectrum has a central wavelength of approximately 1600?nm and a 3?dB bandwidth of 16?nm, which falls within the L-band region. The threshold power for the mode-locked operation is achieved at approximately 52?mW. At pump power of 74?mW, the measured pulse width, pulse energy, and average output power are 70?fs, 18.3?nJ and 7.4?mW respectively. The generated pulses are amplified by a 72.44?mW erbium-doped fiber amplifier before being injected into a 100?m long highly non-linear fiber as the nonlinear medium to generate the SC spectrum. The obtained SC spectrum spans from 1250?nm to more than 1700?nm, with bandwidths of 450?nm at a ?70?dBm output power level. For comparison purpose, the 500?m SMF is removed from the setup and similar measurements are then repeated for this case.     

Detailed analysis of a 40 GHz all-optical synchronization based on an amplified-feedback distributed feedback laser

We demonstrate an all-optical synchronization using an amplified-feedback distributed feedback laser with coherent injection experimentally, which can synchronize 40 GHz degraded signals even with optical signal-to-noise ratio as low as 5 dB, or chromatic dispersion as large as 408 ps/nm. Besides, this optical synchronization has a large range of power operation, i.e. high sensitivity of synchronization, from -21.40 dBm to -8.23 dBm, as well as a large frequency-locking range of 190 MHz.