基于MZM的RZ/CSRZ-DQPSK信号产生的新方法

差分相移键控(DPSK)和差分正交相移键控(DQPSK)对光纤非线性具有很高的容忍度,且灵敏度高,在高速、高频谱效率系统中具有优越性。提出了一种基于双驱动马赫-曾德尔调制器(MZM)的差分正交相移键控归零码(RZ-DQPSK)和差分正交相移键控载波抑制归零码(CSRZ-DQPSK)信号产生的新方法。利用一个双驱动MZM实现DQPSK调制,另一个MZM实现波形切割,生成RZ/CSRZ-DQPSK信号。给出了详细的理论推导过程。该方法简化了高速RZ/CSRZ-DQPSK光信号的产生过程,减少了调制器个数。仿真结果表明,CSRZ-DQPSK信号载波频率分量被抑制,具有比RZ-DQPSK信号更紧凑的频谱结构,采用平衡相干检测接收方法接收到的信号有清晰的眼图。     

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.     

光通信系统传输性能的对比分析

分析了载波抑制归零码(CSRZ)、差分相移键控(DPSK)和差分正交相移键控(DQPSK)三种调制格式的频域特性,并使用Optisystem软件对这三种码在40Gb/s光通信系统中的灵敏度、非线性效应和色散容限进行了对比。     

改进型双二进制归零码信号在标记交换系统中的新应用

提出以改进型双二进制归零码(MD-RZ)信号作为标记,分别采用差分相移键控非归零码(NRZ-DPSK)信号和差分正交相移键控非归零码(NRZ-DQPSK)信号作为载荷进行正交调制的新方案.然后提出了一种从标记信号中提取和恢复时钟的简单方案.比较了背对背系统中2.5 Gbit/s的MD-RZ标记叠加到10 Gbit/s的NRZ-DPSK载荷和20 Gbit/s的NRZ-DQPSK载荷上的频谱特性,证明了MD-RZ标记占空比越大,光分组信号的频带利用率越高.采用传统的二进制强度调制-直接检测(IM-DD)系统的接收机检测得到了背对背系统中不同占空比的2.5 Gbit/s MD-RZ标记的眼图.结果表明,若采用色散补偿技术,两种光分组信号中的MD-RZ标记能够在长距离传输时克服接收端眼图的失真;当入纤功率值高于18 dBm时,占空比取值越大,MD-RZ标记的眼开度代价具有越高的传输鲁棒性.     

光纤通信系统中新型调制格式分析

从理论上分析马赫曾德尔调制器对光信号的调制原理,对几种基于马赫曾德尔调制器的主要调制格式,如归零码（RZ）、抑制载波归零码（CSRZ）、单边带调制（SSB）,归零差分相移键控码（RZ-DPSK）、抑制载波归零差分相移键控（CSRZ-DPSK）的产生原理以及实现方法进行分析和论述,并进一步运用光通信系统仿真软件进行了波形...     

基于CSRZ码的DQPSK多级相位调制技术的研究

文章从理论上推导出了载波抑制归零(CSRZ)码和差分正交相移键控(DQPSK)的调制解调原理公式,给出了实现的具体过程,以及仿真得到的调制后的频谱图和解调后的眼图.结果表明,CSRZ-DQPSK作为新型多级相位调制格式具有更窄的频谱宽度、更高的频谱效率,解调后的眼图也很好,有望成为下一代光纤通信系统的首选传输码型.     

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.     

光DQPSK调制在不同色散补偿系统中的性能

分析了光非归零-差分正交相移键控(NRZ-DQPSK)、33%归零-差分正交相移键控(33%RZ-DQPSK)和载波抑制归零-差分正交相移键控(CSRZ-DQPSK)三种调制格式的频域特性。并数字仿真了40Gbit/s的单信道光纤系统中三种调制格式在对色散(CD)进行后补偿、预补偿和对称补偿等三种补偿方式及考虑偏振模色散(PMD)和非线性效应情况下的传输性能。仿真结果表明,33%RZ-DQPSK对自相位调制(SPM)有最好的容忍度,但缓解PMD和CD的能力较弱;CSRZ-DQPSK在色散后补偿方式中对PMD和非线性效应具有最好的抑制能力。     

8×40Gbit/sWDM系统中CSRZ-DQPSK性能数值分析

通过求解耦合非线性薛定谔方程,数值分析了8×40 Gbit/s波分复用(WDM)系统中色散、偏振模色散(PMD)、非线性效应和信道间距对载波抑制归零-差分正交相移键控(CSRZ-DQPSK)调制格式的影响.结果表明不同信道间传输特性相似,而在高速、窄信道间距的WDM系统中偏振模色散(PMD)和非线性效应的影响会进一步加剧.当入纤功率从8 dBm增大到11 dBm时,CSRZ-DQPSK调制格式Q值从7.8dB线性降低到2.8dB,而当信道间距低于100 GHz后系统性能急速变差.     

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.     

RZ/CSRZ-DPSK and chirped NRZ signal generation using a single-stage dual-electrode Mach-Zehnder modulator

This letter presents a novel configuration for return-to-zero (RZ) differential phase-shift keyed (DPSK), carrier-suppressed (CS) RZ DPSK, and chirped nonreturn-to-zero (CNRZ) signal generation, which only requires a single-stage dual-electrode Mach-Zehnder modulator (DE-MZM). RZ-DPSK, CSRZ-DPSK, or CNRZ signals can be generated via the same configuration by changing the DE-MZM operating conditions. Analytical derivation and simulation on signal generation and wavelength-division-multiplexed transmission was also carried out to justify the equivalence of the proposed scheme and conventional methods. The proposed scheme is expected to be more cost-effective due to the reduction in required modulator number.     

Advanced data modulation techniques for WDM transmission

This article discusses the various schemes for generating typical advanced modulation formats in terms of configuration and cost, and particularly presents some recently proposed configurations for optical data generation with better performance or reduced components, including pulsed multichannel source generation for return-to-zero (RZ)-based WDM application, multichannel dual-mode pulse source for carrier-suppressed RZ (CSRZ)-based WDM application, CSRZ and CSRZ differential phase shift keyed (DPSK) signal generation using a single Mach-Zehnder modulator (MZM) together with an electrical mixer, chirped RZ generation with reduced modulator number, and RZ/CSRZ-DPSK generation using a single dual-drive MZM and optical minimum shift keying (MSK).     

All-Optical Format Conversions Using Periodically Poled Lithium Niobate Waveguides

We investigate all-optical format conversions by using cascaded second-order nonlinearities in periodically poled lithium niobate (PPLN) waveguides. Analytical solutions under non-depletion approximation with clear physical insights are derived, showing operation principles of various PPLN-based format conversions. We propose and theoretically demonstrate all-optical 40 Gb/s nonreturn-to-zero (NRZ) to carrier-suppressed return-to-zero (CSRZ), nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) to return-to-zero differential phase-shift keying (RZ-DPSK), and NRZ-DPSK to carrier-suppressed return-to-zero differential phase-shift keying (CSRZ-DPSK) format conversions based on cascaded sum- and difference-frequency generation (cSFG/DFG). Tunable all-optical 20 Gb/s NRZ to return-to-zero (RZ) format conversion based on cascaded second-harmonic generation and difference-frequency generation (cSHG/DFG) is successfully confirmed in the experiment by setting NRZ signal at SHG quasi-phase matching (QPM) wavelength. Moreover, we experimentally report for the first time, PPLN-based all-optical 40 Gb/s NRZ-to-CSRZ, NRZ-to-RZ, and NRZ-DPSK-to-RZ-DPSK format conversions.      

采用滤波技术提高不同码型差分群时延动态范围研究

采用宽带滤波、窄带滤波和非对称滤波3种滤波技术,将其分别应用于归零码（RZ）、载波制RZ（CSRZ）、差分相移键控RZ（RZ-DPSK）和差分相移钯控的载波抑制RZ（CSRZ—DPSK）4种不同码型的系统中,数值模拟结果表明,滤波技术确能提高差分群时延（DGD）的监控范围;在3种滤波技术中,以窄带滤波技术适合每种码型并使用DGD响应范围最大而具有更好的优势。实验验证了滤波技术提高DGD响应范围的有效性。     

WDM PON using 10-Gb/s DPSK downstream and re-modulated 10-Gb/s OOK upstream based on SOA

A signal remodulation scheme of 10-Gb/s differential phase-shift keying(DPSK) downstream and 10-Gb/s on-off keying(OOK) upstream using a semiconductor optical amplifier(SOA) and a Mach-Zehnder intensity modulator(MZ-IM) at the optical networking unit(ONU) side for wavelength division multiplexed passive optical network(WDM PON) is proposed.Simulation results indicate that error-free operation can be achieved in a 20-km transmission,and the receiver sensitivity of return-to-zero differential phase-shift keying(RZ-DPSK) is higher than nonreturn-to-zero differential phase-shift keying(NRZ-DPSK) in the proposed scheme.     

Amplitude Regeneration of RZ-DPSK Signals in Single-Pump Fiber-Optic Parametric Amplifiers

The input power tolerance of a single-pump fiber-optic parametric amplifier (FOPA) is experimentally shown to be enhanced for return-to-zero differential phase-shift keying (RZ-DPSK) modulation compared to RZ on–off keying modulation at 40 Gb/s. The improved nonlinear tolerance is exploited to demonstrate amplitude regeneration of a distorted RZ-DPSK signal in a gain-saturated FOPA. An optical signal-to-noise ratio penalty of 3.5 dB after amplitude distortion is shown to be reduced to 0.2 dB after the FOPA, thus clearly demonstrating the regenerative nature of saturated FOPAs for RZ-DPSK modulation.      

All-Optical Chromatic Dispersion Monitoring for Phase-Modulated Signals Utilizing Cross-Phase Modulation in a Highly Nonlinear Fiber

We propose and experimentally demonstrate an all-optical chromatic dispersion (CD) monitoring technique for phase-modulated signals utilizing the cross-phase-modulation effect between the input signal and the inserted continuous-wave probe. The probe's optical spectrum changes with the accumulated CD on the input signal, indicating that the optical power variations can be measured for monitoring. The experimental results show that this technique can monitor up to 120 ps/nm of CD for a 40-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) transmission system, with the maximum measured optical power increment of 16.5 dB. The applicability of this monitoring technique to higher bit-rate phase-modulated signals, such as 80-Gb/s RZ differential quadrature phase-shift keying and 80-Gb/s polarization-multiplexed RZ-DPSK, is also investigated via simulation.      

差分相移键控的非归零到归零格式转换研究

提出了一种全新的基于相位-强度混合调制和色散补偿的光差分相移键控(DPSK)信号的非归零(NRZ)到归零(RZ)格式转换器,理论分析了转换器参数对转换的影响,数值研究了恶化条件下的10 Gb/s的NRZ-DPSK到RZ-DPSK的格式转换。实验展示了10 Gb/s的DPSK信号格式转换及解调后的误码性能。计算结果表明,通过设计转换器参数可获得低占空比RZ-DPSK信号,且转换后信号质量较高。实验结果表明格式转换功率代价较低,转换后RZ-DPSK信号时间抖动较原NRZ-DPSK信号减小。该格式转换器还适合光四相差分相移键控(DQPSK)的非归零到归零格式转换及多波长操作。