光纤传输系统中基于相位预调制的信号整型

利用相位预调制技术解决高速长距离光纤传输系统中面临的接收灵敏度降低和色散容限问题。通过在发射端对非归零(NRZ)的光信号进行比特同步相位预调制,使非归零码在传输过程中得到波形重整,演变为归零(RZ)的波形,从而提高眼图开启度。实验观测了普通非归零码和相位预调制的非归零码在不同相位调制深度和色散下的光谱、眼图和功率代价。10Gb/s的传输结果表明,链路色散绝对值小于1000ps/nm时,施加相位预调制的非归零信号功率代价小于1dB,比普通非归零信号具有更高的接收灵敏度和更低的色散功率代价。因此,基于相位预调制的信号整型技术可减轻系统对光信噪比和色散管理的要求,延长传输距离。     

16×40Gbit/s DWDM系统色散补偿和调制方式研究

对传输容量为16×40Gbit/s、传输距离为500～2 000km的DWDM(密集波分复用)系统进行了研究。分析了不同调制方式(CSRZ(载波抑制归零)码、DRZ(双二进制归零)码和MDRZ(改进的双二进制归零)码)、不同色散补偿方案(前置、后置和中间色散补偿)对系统传输性能的影响。仿真结果表明,当传输距离超过1 500km后,MDRZ码能够很好地抑制FWM(四波混频)效应,提高系统性能;中间色散补偿方案比前置色散补偿和后置色散补偿有更好的补偿效果。     

三种载波抑制归零码光调制格式性能

首先分析了基于载波抑制归零码的光载波抑制归零-开关键控(CSRZ-OOK)、载波抑制归零-差分相移键控(CSRZ-DPSK)和载波抑制归零-差分正交相移键控(CSRZ-DQPSK) 三种光调制格式的时域和频域特性,并数字仿真了其在40 Gbit/s单信道光纤系统中的传输性能.以Q值、眼图和误码率(BER)作为性能评价指标,研究了这三种调制格式对色散(CD)、偏振模色散(PMD)和非线性效应的抑制作用.结果表明:CSRZ-DQPSK相对于CSRZ-OOK、CSRZ-DPSK对色散、偏振模色散和非线性效应有非常好的容忍能力.     

基于光纤差分相移键控的色散补偿方案的研究

为了研究光差分相移键控(DPSK)调制格式在光纤高速传输系统中的色散补偿, 利用色散补偿光纤(DCF)的色散补偿原理, 对40Gbit/s光纤传输系统进行色散补偿, 分析了40Gbit/s单通道光纤传输系统中3种DPSK调制格式信号的频谱特性; 仿真了3种码型的色散容忍度以及3种调制格式在考虑光纤的非线性下的色散补偿方案。结果表明, 光非归零码差分相移键控(NRZ-DPSK)信号具有最好的色散容忍度, 但其受非线性的影响比较大; 33%归零码差分相移键控(33%RZ-DPSK)信号的色散容忍度差, 但其色散补偿后的效果优于NRZ-DPSK; 而载波抑制归零码差分相移键控信号对色散和非线性效应都有较好的抑制; 3种DPSK调制格式均在对称补偿2方案中色散补偿的效果最佳。此仿真研究对光DPSK信号在光纤中的色散补偿具有参考意义。     

四种级联差分相位调制码的100 Gbit/s传输

在级联相位调制的100 Gbit/s光信号传输系统中,对差分相移键控非归零码(NRZ-DPSK)、差分相移键控归零码(RZ-DPSK)、差分四相相移键控非归零码(NRZ-DQPSK)和差分四相相移键控归零码(RZ-DQPSK)进行了比较研究.当四种信号通过90 km的标准单模光纤(SMF)和16 km的色散补偿光纤(DCF)传输后,在满足相同入纤功率的条件下,NRZ-DQPSK信号具有最高的色散容限;如果仪仪考虑一阶偏振模色散(PMD),RZ-DQPSK信号具有最优的抗偏振模色散特性;当入纤功率在O～10 dBm的范围内凋节时,RZ-DPSK信号具有最好的非线性容忍度;最后比较了四种相位调制码型传输后通过不同带宽的三阶高斯滤波器后的接收性能,得出滤波器带宽值大于125 GHz后,NRZ-DPSK信号的接收性能最佳.     

高速密集波分复用系统中的二级调制格式研究

论述了强度调制直接检测(IM-DD)高速密集波分复用(DWDM)系统的二级调制原理，并从马赫-曾德尔调制器的传递特性出发推导了四种调制格式[全频率调制归零码(FFMRZ)、半频率调制归零码(HFMRZ)、单边带调制归零码(SSBRZ)、载波抑制归零码(CSRZ)]。根据信号光眼图及归一化频谱描述了各种码型的时频特征。在此基础上分别对各种码型的色散容限、非线性容限进行了数值仿真，通过比较眼图张开度损伤(EOP)发现对于单波长系统载波抑制归零码传输性能最优。最后利用全面的密集波分复用系统模型计算了各种码型的Q因子，发现载波抑制归零码的性能仍然保持最优，这种优势在考虑偏振模色散(PMD)的情况下更为突出。因此载波抑制归零码是强度调制直接检测系统较好的选择。     

40Gb/sWDM系统中RZ&NRZ调制格式的性能比较

利用数值计算的方法对40G WDM系统进行了仿真.在考虑了光纤群速度色散(GVD)、三阶色散(TOD)、自相位调制(SPM)、交叉相位调制(XPM)、四波混频(FWM)和偏振模色散(PMD)的前提下,通过对比眼图和Q因子,对归零码(RZ)和非归零码(NRZ)调制格式的传输性能进行了研究.     

基于HNLF的RZ到NRZ的全光码型转换

数值仿真分析了利用高非线性光纤(HNLF)的交叉相位调制(XPM)效应实现归零(RZ)码到非归零(NRZ)码的转换,并讨论了RZ信号占空比、光纤色散对转换后NRZ信号Q因子的影响.数值结果表明:转换后NRZ码的Q值受输入RZ信号占空比的影响;而且RZ信号与连续的探测光之间的色散差也严重影响转换后NRZ信号的Q因子值.     

高速光传输系统中八进制差分相位幅度键控性能分析

高级光调制格式能够有效抑制随信道速率的增加而给系统带来的色散、非线性等传输损伤,是高速光传输系统的关键技术之一.研究了基于马赫-曾德尔凋制器(MZM)产生的八进制差分相位幅度键控非归零码(NRZ-ODPASK)、八进制差分相位幅度键控归零码(RZ ODPASK)以及八进制差分相位幅度键控载波抑制归零码(CSRZ-0DPAsK)在40 Gbit/s速率下的传输性能.结果表明,RZ-ODPASK调制格式抗色散能力较强,且相位支路的色散容限均大于幅度支路;在波分复用(WDM)系统中,CSRZ-ODPASK信道间串扰代价比NRZ-ODPASK和RZ-ODPASK分别小0.81 dB和0.19 dB,更加适合高速光纤传输系统.     

调制码型对WDM-PON混合调制系统性能的影响

文章对上下行数据流分别使用差分相移键控(DPSK)和开关键控(OOK)不同的混合调制方式,通过比较下行采用不同调制码型,在没有色散补偿的情况下,实现了20 km、上下行10 Gbit/s对称速率的传输.结果表明,使用反向归零 (IRZ) 码的混合调制方式可以使下行数据流具有较高的消光比,上行数据流具有较好的色散容限,从而提高了传输系统的整体性能.     

40Gb/s光纤通信系统中不同码型传输特性的实验研究

在高速光纤通信系统中码型的选择是决定系统传输质量和光谱效率的主要因素。码型的选择和信道速率、信道波长间隔、光放大器的选择、光放大器放置间隔、光纤的类型、色散管理策略等各种因素密切相关。分析了非归零码（NRZ）、归零码（RZ）和载波抑制归零码（CSRZ）码型的产生方式及特点。采用单信道和掺铒光纤放大器（EDFA）放大方式对三种码型进行了40Gb/s的100kmG.652光纤通信传输实验。比较了三种码型的系统传输持性、最佳入纤功率和不同入纤功率下的功率代价：载波抑制归零码最佳入纤功率为9dBm，功率代价小于非归零码和归零码。结果表明，在相同的色散补偿条件下，载波抑制归零码比归零码和非归零码有更优的非线性容忍度。     

Experimental demonstration and analysis of all-optical label swapping based on RZ-DQPSK/IRZ-ASK modulation format

A novel optical return zero differential quadrature phase shifted keying/inverse return zero amplitude shifted keying(RZ-DQPSK/IRZ-ASK) orthogonal modulation format scheme for all-optical label swapping is analyzed theoretically and experimentally.The transmission characteristics of RZ-DQPSK/IRZ-ASK modulation format transmission system are demonstrated.Results show that high extinction ratio is obtained for IRZ-ASK label signal while at the same time the all-optical label swapping,differential quadrature p...     

Centralized light-wave WDM-PON employing DQPSK downstream and 00K remodulated upstream signals

A novel architecture for wavelength-division-multiplexing passive optical network (WDM-PON) with centralized light-wave is proposed and demonstrated. At the optical line terminal (OLT) session of this architecture, optical differential quadrature phase shift keying (DQPSK) modulated signal with constant-intensity at 10 Gbit/s is utilized for downstream transmission. At the optical network unit (ONU), part of the downstream optical power is remodulated with on-off keying (OOK) intensity modulation at 10 Gbit/s for upstream without additional laser. Simulation results show that the power penalties of the downstream for 20 km single-mode fiber (SMF) transmission and multi-channels are negligible. While for the upstream, the power penalties are obvious. The simulation results and analysis also reflect that by reducing the launch power of DQPSK transmitters, power penalties can be reduced, although the transmission distance is limited.     

WDM-POLSK Transmission Systems by Using Semiconductor Optical Amplifiers

The authors demonstrate the potential of using POLarization Shift Keying (POLSK) modulation format combined with semiconductor optical amplifiers (SOAs) in wavelength division multiplexing (WDM) transmission systems. The constant intensity of the POLSK modulation format allows for substantial removal of cross-gain-modulation impairments in SOAs so that practical amplifier spacing values (more than 100 km) are demonstrated in various different experimental configurations. Record WDM transmission experiments at 10 Gb/s by using SOA-based amplification are presented in short and medium reach system architectures using either single mode fiber or nonzero dispersion shifted fiber     

Centralized light-wave WDM-PON employing DQPSK downstream and OOK remodulated upstream signals

A novel architecture for wavelength-division-multiplexing passive optical network(WDM-PON)with centralized light-wave is proposed and demonstrated.At the optical line terminal(OLT)session of this architecture,optical differential quadrature phase shift keying(DQPSK)modulated signal with constant-intensity at 10 Gbit/s is utilized for downstream transmission.At the optical network unit(ONU),part of the downstream optical power is remodulated with on-off keying(OOK)intensity modulation at 10 Gbit/s for upstream without additional laser.Simulation results show that the power penalties of the downstream for 20 km single-mode fiber(SMF)transmission and multi-channels are negligible.While for the upstream,the power penalties are obvious.The simulation results and analysis also reflect that by reducing the launch power of DQPSK transmitters,power penalties can be reduced,although the transmission distance is limited.     

超高速全光信息处理

P比特级光交换网络的发展,要求网络在传输、复用和交换方式上具有灵活性、多样性和高效性,因此基于超高速全光信息处理的网络功能存在较大价值。利用不同光子材料非线性效应(SPM\XPM\FWM等)已成功实现了组播、码型变换、逻辑门等不同的全光信息处理单元技术,其中高非线性光纤以其易与现有光纤网络相融合和成本相对较低等特点而具有较大潜力。在总结光信息处理的相关研究进展的基础上,文章重点介绍了偏振复用(PDM)系统中的高速全光信息处理技术,包括基于自相位调制效应(SPM)的全光再生和基于交叉相位调制效应(XPM)的波长转换实现。     

FSK Modulation Scheme for High-Speed Optical Transmission

In this paper,we describe the generation,detection,and performance of frequency-shift keying (FSK) for high-speed optical transmission and label switching.A non-return-to-zero (NRZ) FSK signal is generated by using two continuous-wave (CW) lasers,one Mach-Zehnder modulator (MZM),and one Mach-Zehnder delay interferometer (MZDI).An RZ-FSK signal is generated by cascading a dual-arm MZM,which is driven by a sinusoidal voltage at half the bit rate.Demodulation can be achieved on 1 bit rate through one MZDI or an array waveguide grating (AWG) demultiplexer with balanced detection.We perform numerical simulation on two types of frequency modulation schemes using MZM or PM,and we determine the effect of frequency tone spacing (FTS) on the generated FSK signal.In the proposed scheme,a novel frequency modulation format has transmission advantages compared with traditional modulation formats such as RZ and differential phase-shift keying (DPSK),under varying dispersion management.The performance of an RZ-FSK signal in a 4 × 40 Gb/s WDM transmission system is discussed.We experiment on transparent wavelength conversion based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) and in a highly nonlinear dispersion shifted fiber (HNDSF) for a 40 Gb/s RZ-FSK signal.The feasibility of all-optical signal processing of a high-speed RZ-FSK signal is confirmed.We also determine the receiver power penalty for the RZ-FSK signal after a 100 km standard single-mode fiber (SMF) transmission link with matching dispersion compensating fiber (DCF),under the post-compensation management scheme.Because the frequency modulation format is orthogonal to intensity modulation and vector modulation (polarization shift keying),it can be used in the context of the combined modulation format to decrease the data rate or enhance the symbol rate.It can also be used in orthogonal label-switching as the modulation format for the payload or the label.As an example,we propose a simple orthogonal optical label switching technique based on 40 Gb/s FSK payload and 2.5 Gb/s intensity modulated (IM) label.     

Influence of nonlinear effects on 6.4 Tb/s dual polarization quadrature phase shift keying modulated dense wavelength division multiplexed system

In this paper, we have proposed a high‐performance transmission system of 32 channels based on dense wavelength division multiplexing (DWDM) through an optical fiber link consisting of 110 km per span. To check the influence of nonlinear effects, we have considered phase modulation (SPM), cross‐phase modulation (XPM), four‐wave mixing (FWM), stimulated Raman scattering (SRS), and self‐steepening (SS) which limits the performance of optical communication systems. In the proposed system, each channel is modulated at 200 Gbps of dual‐polarization quadrature phase shift keying (DP‐QPSK) format, with a 50‐GHz grid yield whole data rate of 6.4 Tbps. The results have proved that the nonlinear phenomena degrade the performance of proposed optical fiber communication systems, and XPM has the most dominant effect, followed by SS, SRS, and SPM. The simulation was carried out with Optisystem 14 which is powerful software for modeling and simulation of optical fiber transmission.     

Combining self-phase modulation and optimum modulation conditionsto improve the performance of 10-Gb/s transmission systems using MQWMach-Zehnder modulators

For 10-Gb/s transmission over nondispersion shifted fiber, the combined use of self-phase modulation (SPM) and joint optimization of the bias and modulation voltages to increase the dispersion limited transmission distance is considered for multiple quantum well Mach-Zehnder modulators. For the dual drive (push-pull) modulation format, the dependence of the receiver sensitivity on fiber length and average transmitted optical power is determined for both conventional and π phase-shift modulators with either symmetric or asymmetric Y-branch waveguides. When SPM is negligible and the optical extinction ratio is maximized, the modulator design must he considered carefully in order to increase the transmission distance. By combining SPM and optimum modulation conditions, the dependence of the system performance on the modulator design is reduced substantially. For an average transmitted optical power of 12.5 dBm, the receiver sensitivity for transmission over 140 km of fiber varies by only 0.3 dB for the different modulator designs. This compares with a variation of 3.1 dB for maximum extinction ratio modulation