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.     

A novel orthogonal modulation format of D8PSK/ASK with differential bi-phase encoding and its application in a label switching optical network

The principle of a novel orthogonal modulation format of differential 8-level phase-shift keying amplitude-shift keying (D8PSK/ASK) with differential bi-phase encoding (DBC) is introduced. Based on it, an optical labeling scheme, in which the payload is 100 Gbit/s D8PSK signal and the label is 10 Gbit/s DBC-ASK signal, is proposed and simulated. The results are compared with other current schemes, and the effects of transmission range, modulation extinction ratio (ER) and received power on system performance are analyzed, respectively. The results show that the spectrum efficiency and bit error rate (BER) are improved greatly, and when the modulation ER is increased to 11 dB, the balanced performance between the payload and label is achieved.     

一种基于D8PSK／ASK正交调制的新型光标记方案研究

深入研究了差分八相移键控（I）8PSK）j幅移键控（AsK）正交调制格式的机理,提出了一种基于D8PsKjASK正交调制的新型光标记方案,利用D8PSK作为载荷的调制方式,ASK作为标记的调制方式,仿真实现了载荷120Gb／s、标记10Gb／s的传输速率。分析了信号的消光比（ER）对误码率（BER）的影响,仿真结果表明...     

A WDM-PON with DPSK modulated downstream and OOK modulated upstream signals based on symmetric 10 Gbit/s wavelength reused bidirectional reflective SOA

We investigate a wavelength-division-multiplexing passive optical network (WDM-PON) with centralized lightwave and direct detection. The system is demonstrated for symmetric 10 Gbit/s differential phase-shift keying (DPSK) downstream signals and on-off keying (OOK) upstream signals, respectively. A wavelength reused scheme is employed to carry the upstream data by using a reflective semiconductor optical amplifier (RSOA) as an intensity modulator at the optical network unit (ONU). The constant-intensity property of the DPSK modulation format can keep high extinction ratio (ER) of downstream signal and reduce the crosstalk to the upstream signal. The bit error rate (BER) performance of our scheme shows that the proposed 10 Gbit/s symmetric WDM-PON can achieve error free transmission over 25-km-long fiber transmission with low power penalty.     

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。     

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.     

啁啾管理调制格式在高速接入网中传输分析

物联网、虚拟现实及人工智能等技术的发展加大了对光纤接入无源光网络带宽的需求,其中调制器成为制约无源光网络带宽的关键因素。结合了直接调制激光器和外调制器各自优势的啁啾管理激光器以产生结构简单、便于集成等特点受到了广泛关注。采用耦合速率方程理论研究了啁啾管理激光器的动力学特性,分析了40 Gbit/s啁啾管理调制格式的产生原理及时频域特性,并在高速无色散补偿接入网中与由外调制器产生的40 Gbit/s非归零调制格式进行了性能对比。结果表明,带宽为48.5 GHz的40 Gbit/s啁啾管理调制格式在1 dB灵敏度代价下所对应的色散容限为215 ps/nm,与非归零调制格式相比其无色散补偿传输距离增加了1.6倍,表现出了强的抗色散能力,在高速接入网中也体现了较高的应用价值。相关结果可为实际系统设计提供理论参考。     

A novel chromatic dispersion monitoring method for 400 Gbit/s 256 QAM fiber-optic system based on asynchronous amplitude sampling

A novel chromatic dispersion (CD) monitoring technique based on asynchronous amplitude sampling (AAS) is proposed for a higher modulation format and higher rate system. The dispersion and other impairment factors can be separated with the definition of monitoring parameter M. A 400 Gbit/s 256 quadrature amplitude modulation (QAM) system is built using Optisystem13.0 beta software. Simulations of CD monitoring technique for different bandwidths of sampling Gaussian filter, optical signal to noise ratios (OSNRs) and duty cycles are investigated, and the tolerance is also discussed. Simulation results show that the method can be less affected by noise, and a higher accuracy of 600 ps/(nm.km) can be achieved. The technique supports a wide range of data traffic and enhances operation flexibility of optical networks.     

多种调制格式微波信号的光学产生方案

提出了一种基于偏振调制器（PolM）和Sagnac环级联的多调制格式微波信号的光学产生方案。理论分析了PolM在基带编码信号的驱动下产生偏振键控（PolSK）信号的基本原理,Sagnac环中嵌有两个马赫增德尔调制器（MZM）,分别对顺时针和逆时针传输的PolSK信号进行独立调制。通过合理调整两个MZM的驱动信号,实现了幅移键控（ASK）、频移键控（FSK）和相移键控（PSK）微波信号的产生。在仿真实验中,产生了比特率为2 Gbit/s的40 GHz ASK信号、20/40 GHz FSK信号和20 GHz PSK信号,同时验证了比特率和载波频率的宽带可调谐性。Sagnac环结构提升了系统的稳定性,并且针对每种调制格式的微波信号,在不改变链路结构的情况下其比特率和载波频率都可以通过控制基带编码信号和MZM的射频驱动来进行独立且灵活的调谐。     

Linewidth-tolerant 30 Gbit/s 8-PSK self-homodyne using single modulator and phase-noise cancelling technique

Linewidth-tolerant 8-ary phase-shift keying (8-PSK) self-homodyne modulation/demodulation at symbol rates of 10 Gsymbol/s (30 Gbit/s) and 1 Gsymbol/s (3 Gbit/s) using a distributed-feedback laser diode with a linewidth of 30 MHz and a single modulator is experimentally demonstrated. Owing to the phase-noise cancelling capability of the self-homodyne scheme based on a polarisation-multiplexed pilot-carrier, a floorless bit error rate performance of <10^-9 was achieved; this value was obtained even for the symbol rate of 1 Gsymbol/s, at which the required linewidth condition is stringent. Furthermore, the tolerances against differential group delays and dispersion at the symbol rate of 10 Gsymbol/s have been evaluated.     

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。     

Coherent Equalization and POLMUX-RZ-DQPSK for Robust 100-GE Transmission

We discuss the use of a coherent digital receiver for the compensation of linear transmission impairments and polarization demultiplexing in a transmission system compatible with a future 100-Gb/s Ethernet standard. We present experimental results on the transmission performance of 111 Gbit/s POLMUX-RZ-DQPSK. For a dense WDM setup with channels carrying 111 Gbit/s with a 50 GHz channel spacing (2.0 bits/s/Hz), we show the feasibility of 2375 km transmission. This is enabled through coherent detection which results in excellent noise performance, and subsequent electronic equalization which provides the high tolerance to polarization mode dispersion and chromatic dispersion (CD). Furthermore, we discuss the impact of sampling and digital signal processing with either 1 or 2 samples/bit. We show that when combined with low-pass electrical filtering, 1 sample/bit signal processing is sufficient to obtain a large tolerance towards CD. The proposed modulation and detection techniques enable 111 Gbit/s transmission that is directly compatible with the existing 10 Gbit/s infrastructure.     

D8PSK调制格式研究及其传输性能分析

研究了基于相位调制原理的新型调制格式差分八相相移键控(D8PSK),给出了串联和并联两种信号生成方案,对包括非归零码(NRZ)、33%占空比归零码(33%RZ)、50%占空比归零码(50%RZ)、载波抑制归零码(CSRZ)4种不同码型的生成方式进行了说明,对信号的接收过程和预编码公式进行了理论推导,并对系统进行了仿真。仿真系统中信号总速率达到100 Gbit/s,信号生成采用串联方式,信号接收采用4个马赫-曾德尔时延干涉仪(MZI)平衡检测接收机,色散补偿方式采用对称补偿,通过眼图可以看到其接收效果良好。最后对不同码型的D8PSK与DQPSK系统在抵抗群速度色散效应、非线性效应及偏振模色散效应3种主要影响系统传输性能的因素方面进行了分析比较。当眼图张开度代价为1dB时,CSRZ-D8PSK信号的群速度色散容限、非线性容限及偏振模色散容限分别为190ps/nm、4.4 dBm及24 ps,结果表明其具有较好的传输性能。     

A dispersion flattened fiber front-haul transmission system with high bitrate signal at low input optical power

We propose a dispersion flattened fiber (DFF) front-haul transmission system with high bitrate, polarization multiplexing (PM) and quadrature amplitude modulation (QAM) signal at low input optical power. The modulation format of the system is PM-16QAM, and the bitrate is 256 Gbit/s. The transmission characteristics over DFF link system are experimentally studied, which are compared with those over non-zero dispersion shifted fiber (NZDSF) link and standard single mode fiber (SSMF) link. The experimental results show that the error vector magnitude (EVM) of 256 Gbit/s and PM-16QAM signal over 25 km DFF link is 0.75% better than that over 25 km NZDSF link at least, and the bit error rate (BER) and Q-factor are much better than those of NZDSF. Their EVM and BER are both decreased with the increase of input optical power, and the Q-factor is increased. Those characteristics over 25 km SSMF are the worst at the same case. The larger the dispersion is, the more the constellation points are deviated from their respective centers and the worse the constellation characteristics are. The greater the attenuation of the DFF is, the smaller the input power of the DFF is, the more the constellation points are deviated from their centers and the worse the constellation characteristics are. This study provides a new idea and experimental support for long span front-haul propagation in mobile communication.     

Dispersion compensation by active predistorted signal synthesis

Techniques for the synthesis of an optical signal predistorted to compensate for fiber dispersion are discussed theoretically. A scheme for very high bit rate (>10 Gbit/s) time-division-multiplexed transmission is proposed which neither requires extremely short pulse sources nor suffers from their inherent dispersion limitations. The rudimentary aspects of the techniques have been verified experimentally by demonstrating both enhanced and degraded transmission of a 4-GHz modulated signal at 1.55 μm over 10-30 km of optical fiber.     

Wavelength re-generation and re-modulation using optical phase lock loop techniques for 100-Gb/s DQPSK up-stream transmission in DWDM passive optical networks

We demonstrate, by partial experiment and simulation, a re-modulation scheme of the lightwave carrier imbedded in a downstream optical signals under differential quadrature phase shift keying (DQPSK) modulation format for upstream transmission over passive optical networks (PONs) at a bit rate of 100 Gb/s. The recovery of the optical carrier with the precise wavelength is implemented using an injection laser incorporating an optical phase locked loop (OPLL). In the computer simulation, the OPLL is implemented by a Simulink model consisting of interconnected system blocks following exactly the physical phenomena of the hardware structures. This model is then integrated with DQPSK modulation formats for up- and down-transmissions in PONs. Pulse shaping of Non-Return-to-Zero and Return-to-Zero (RZ) of 50% duty cycle and 67% duty cycle are used, respectively. Dispersion tolerance of 25 ps/nm with a bit error rate (BER) of 10⁻⁹ is achieved for both down- and upstream transmissions over fully dispersion compensated 80- km standard SMF and 1.5- km SSMF equivalent dispersion with carrier suppressed RZ pulse shaping (CS-RZ 67%). The contribution to BER by the timing synchronization error at the sampling of the optical network unit for re-modulation and related power penalty of these modulation formats is also investigated. It is noted that using the optical phase locking technique it is possible to remove any cross talks which may be generated from nonlinear effects such as cross-phase modulation, self-phase modulation, and four wave mixing.     

Reduced bandwidth optical digital intensity modulation withimproved chromatic dispersion tolerance

A simple optical modulation scheme using a lithium niobate Mach-Zehnder modulator driven by a three level drive waveform is proposed. The two-level intensity modulated (IM) optical signal obtained possesses a smaller optical bandwidth and thus greater chromatic dispersion tolerance compared with existing two-level IM methods used for high data rate transmission (e.g. 10 Gbit/s)     

High-speed large-signal digital modulation of a 1.3 ?m InGaAsP constricted mesa laser at a simulated bit rate of 16 Gbit/s

Recently, high-frequency 1.3?m InGaAsP constricted mesa lasers have shown a small-signal ?3 dB bandwidth of more than 15 GHz at 15°C, and have been modulated with pseudorandom pulses at 8 Gbit/s (NRZ format). The letter reports large-signal digital modulation of such a constricted mesa laser using time-multiplexed electrical pulses 80 Ps in duration and 125 Ps apart which demonstrates the high-speed modulation capability of this laser at a simulated bit rate of 16 Gbit/s (NRZ).     

全光纤锁模腔结构的全光时钟提取实验研究

分析并实验验证了一种全光纤锁模激光器结构的全光时钟提取方案。方案中,采用高非线性光纤(HNLF)替代传统结构中的半导体光放大器(SOA),利用光纤中的交叉相位调制(XPM)效应实现腔内的非线性调制,避免了以SOA作为非线性光调制器件的锁模激光器全光时钟提取方案中,由于载流子恢复时间较长从而限制工作速率的缺点,以达到突破"电子瓶颈"的目的。理论分析了光纤中交叉相位调制的特性以及环形锁模腔的时钟提取原理,并通过实验,从40Gbit/s的光归零码(RZ)信号中提取出了高质量的光信号时钟。该方案可以直接在更高速率条件下工作。     

Experimental Demonstration and Numerical Simulation of 107-Gb/s High Spectral Efficiency Coherent Optical OFDM

Orthogonal frequency-division multiplexing (OFDM) is a multicarrier modulation format in which the data are transmitted with a set of orthogonal subcarriers. Recently, this modulation format has been actively explored in the field of optical communications to take advantages of its high spectral efficiency and resilience to chromatic and polarization dispersion. However, to realize the optical OFDM at 100 Gb/s and beyond requires extremely high electronic bandwidth for the electronic signal processing elements. In this paper, we investigate orthogonal-band-multiplexed OFDM (OBM-OFDM) as a suitable modulation and multiplexing scheme for achieving bandwidth scalable and spectral efficient long-haul transmission systems. The OBM-OFDM signal can be implemented in either RF domain, or optical domain, or a combination of both domains. Using the scheme of OBM-OFDM, we show the successful transmission of 107 Gb/s data rate over 1000-km standard single-mode fiber (SSMF) without optical dispersion compensation and without Raman amplification. The demonstrated OBM-OFDM system is realized in optical domain which employs 2 $times$ 2 MIMO-OFDM signal processing and achieves high optical spectral efficiency of 3.3 bit/s/Hz using 4-QAM encoding. Additionally, we perform numerical simulation of 107-Gb/s CO-OFDM transmission for both single-channel and wavelength-division-multiplexed (WDM) systems. We find that the $Q$ -factor of OBM-OFDM measured using uniform filling of OFDM subbands is in fact more conservative, in particular, is 1.2 dB and 0.4 dB lower than using random filling for single-channel and WDM systems, respectively.