光纤传输系统中互相位调制和受激拉曼散射串扰噪声的比较研究Ⅰ--单级传输系统

在密集波分复用强度调制直接检测光纤系统中 ,导出了包含互相位调制和受激拉曼散射共同作用的强度/相位矩阵表达式。在计算强度噪声谱的基础上 ,研究了互相位调制和受激拉曼散射的相互耦合并用于密集波分复用系统的噪声分析。分析表明 ,受激拉曼散射主要引入低频串扰噪声 ,而互相位调制主要引入高频串扰噪声。相邻较近信道引入的串扰噪声主要来源于互相位调制 ,相邻较远信道引入的串扰噪声主要来源于受激拉曼散射。在单级传输 (无色散补偿 )系统中 ,系统性能一般首先受到互相位调制的限制     

光纤传输系统中互相位调制和受激拉曼散射串扰噪声的比较研究Ⅱ--级联传输系统

在具有级联光放大器的密集波分复用强度调制一直接检测光纤系统中，导出了包含互相位调制和受激拉曼散射共同作用的强度／相位矩阵表达式。在计算强度噪声谱的基础上，研究了互相位调制和受激拉曼散射的相互耦合并用于密集波分复用系统的噪声分析。在带色散补偿的密集波分复用级联光纤传输系统中(如80信道，信道间距50GHz)，受激拉曼散射引入的串扰噪声功率可能超过互相位调制。最后，给出了密集波分复用系统分析与设计的若干建议。     

自相位调制和交叉相位调制共同作用下抽运探测波结构中的信号扰动研究

针对强度调制直接检测波分复用系统研究了抽运探测波结构中自相位调制和交叉相位调制共同作用下的光信号传输,给出了确定任意抽运信号下的探测波时域波形及强度调制率的理论解析方法,分析了信道间隔、传输速率对于交叉相位调制的影响,发现抽运波自相位调制的作用主要体现在使探测波时域强度调制率有所增大,解析结果和数值仿真能较好地吻合。     

Impacts of dispersion maps on nonlinear distortion in distributed Raman amplified multi-span systems

The influences of dispersion maps on three major nonlinear effects (SPM, XPM and SRS) in distributed Raman amplified fiber transmission systems with periodic dispersion compensation are numerically investigated at identical nonlinear phase shift. The results show that compared with lumped amplification, distributed amplification tends to enhance the SPM/XPM induced penalties provided per span complete DC is used. However, these performance differences can be canceled out by means of optimal dispersion managements. Moreover, distributed Raman amplification can change the optimal dispersion maps for XPM effects. On the other hand, the impacts of SRS crosstalk are mainly determined by wavelength spacing and walk-off parameter, and the effects of dispersion management are quite limited. For a system with properly designed fiber dispersion characteristics, SRS induced waveform distortion can be well suppressed.     

Impact of 2OD and 3OD on SRS- and XPM-induced crosstalk in SCM-WDM optical transmission link

In this paper, the impact of second-order dispersion (2OD), third-order dispersion (3OD) and modulation frequency over stimulated Raman scattering (SRS)- and cross-phase modulation (XPM)-induced crosstalk in sub-carrier-multiplexed (SCM) wavelength division multiplexed (WDM) transmission link has been analyzed. It has been observed that there is significant effect of 2OD, 3OD and modulation frequency on the SRS- and XPM-induced crosstalk in a SCM-WDM transmission link. Here the results for SRS- and XPM-induced crosstalk have been reported with independent and combined higher-order dispersion. It has been observed that XPM-induced crosstalk lies between [−52.8 to −45.3] and [−94.7 to −78.6] dB in the presence of 2OD and 3OD respectively for modulation frequencies varied from 500 MHz to 2.0 GHz, while it is in the range of [−94.4 to −84] and [−128.5 to −117] dB when both SRS and XPM are taken into consideration.     

Characterization of wavelength interleaving in radio-over-fiber systems employing WDM/SCM

A radio-over-fiber (RoF) distribution system incorporating both sub-carrier multiplexing and wavelength division multiplexing (WDM) technologies is presented. This signal is directly modulated onto three high-speed lasers. Bragg filters are employed at the receiver base station in order to both demultiplex the required optical channel, and ensure that the detected signal is single side band (in order to overcome dispersion limitations of the link). System spectral efficiency is optimised by wavelength interleaving. The channel spacing between the WDM channels is varied and the system performance for different values of channel spacing and spectral efficiencies is investigated. The results show that wavelength interleaving is a reliable technique that could be used to increase the spectral efficiency of RoF systems.     

交叉相位调制对非线性光纤环镜中光脉冲传输的影响

基于耦合非线性薛定谔方程，采用分步傅里叶方法分析了在单波长信道和WDM（波分复用）4波长信道中XPM（交叉相位调制）对高速NOLM（非线性光纤环镜）光开关中脉冲传输的影响.数值计算表明：XPM造成NOLM中信号脉冲串扰与畸变，并造成NOLM开关性能的下降.WDM系统NOLM光纤环中的同向传播的各波长之间的XPM串扰比相向脉冲之间的XPM效应的影响更大，并且波长越短输出功率越低，中间信道受XPM的影响所导致的脉座现象和走离效应比两侧波长信道严重.     

Crosstalk in high-speed WDM produced by refractive index fluctuation nonlinear effect

With the development of the ultra-high speed and large capacity, the channel crosstalk cause by nonlinear effects become more apparent. This paper research the crosstalk produced by refractive index fluctuation nonlinear effects, establish the corresponding mathematical models and physical monitoring models. The experiment simulation results show when the input power is less than 50 mW, the channel crosstalk caused by the nonlinear effects is low and can be ignored; when input power greater than 50 mW, the channel crosstalk caused by the nonlinear effects is more high and affect transmission quality; and with the further increase in power, the channel crosstalk caused by SPM and XPM gradual increase, when the input power is greater than 300 mW, the crosstalk caused by SPM and XPM morn than by FWM.     

Reference-frame-independent quantum key distribution of wavelength division multiplexing with multiple quantum channels

Reference-frame-independent quantum key distribution (RFI-QKD) can allow a quantum key distribution system to obtain the ideal key rate and transmission distance without reference system calibration, which has attracted much attention. Here, we propose an RFI-QKD protocol based on wavelength division multiplexing (WDM) considering finite-key analysis and crosstalk. The finite-key bound for RFI-QKD with decoy states is derived under the crosstalk of WDM. The resulting secret key rate of RFI-QKD, which is more rigorous, is obtained. Simulation results reveal that the secret key rate of RFI-QKD based on WDM is affected by the multiplexing channel number, as well as crosstalk between adjacent channels.     

Simulation of diffraction from volume holograms

Coupled wave equations that consider two-dimensional distribution and phases of gratings are derived by using weak grating and slow varying approximation. The result of angular selectivity on rand binary data page shows that each minimum is nonzero and each maximum that is not the middle maximum is a little bit smaller than that on plane wave volume hologram. Angular multiplexing is also modeled using the same method, and the middle page is read out in two different angular spacings. The relationship about PSNR versus angular spacing at different multiplexing pages is analyzed to reflect crosstalk between pages. All simulative results show this method is effective for volume holograms simulation.     

New scheme of two-channel WDM modulation with cascaded attenuated-total-reflection modulators

In this paper, we propose a two-channel WDM modulation system by cascading attenuated-total-reflection (ATR) modulators. This system is free from channel demultiplexing and multiplexing elements. Two independent light signals with 20 nm channel spacing are experimentally demonstrated with modulation crosstalk less than −20 dB between the channels.     

The Effect of SRS on Signal Power in Single mode Silica Fiber in DWDM Optical Communication System with Equally Spaced Channels

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Absolute polar duty cycle division multiplexing over wavelength division multiplexing system

The performance of absolute polar duty cycle division multiplexing (AP-DCDM) over wavelength division multiplexing (WDM) system is presented based on the simulation results. The AP-DCDM signal has narrower bandwidth than conventional time division multiplexing (TDM) signal, which makes its implementation in WDM system advantageous. In this paper, characteristics of AP-DCDM and TDM signals in WDM system are compared at the speed of 40 Gbit/s per channel, for the minimum allowed channel spacing and the chromatic dispersion tolerance. The results clearly show that AP-DCDM performs significantly better than TDM. By using AP-DCDM, 1.28 Tbit/s (32 × 40 Gbit/s) was successfully transmitted over 320 km standard single mode fiber. Spectral efficiency of 0.64 b/s/Hz was achieved by using 10 Gbit/s transmitters and receivers without polarization multiplexing.     

The Effect of SRS on Signal Power in Single-mode Silica Fiber in DWDM Optical Communication System with Equally Spaced Channels

Assuming that the Raman gain profile of silica fiber is a triangular function, we derive analytic solutions of N-channel steady-state forward SRS coupling wave equation with equal (but arbitrary) channel spacing. Considering the SRS cross coupling among N-channels, the analytic solutions are applicable to arbitrary signal light power. The results point out that the sequence mi=pi(z)/pi(0) [pi(z) and pi(0) is the power of signal light of i-th channel at transmission length z and 0, respectively. i=1,2,...N] maintains a geometric progression with the common ratio q in the transmission process. The common ratio q varies as a exponential function of the effective transmission length, the sum of input light power and the channel spacing, respectively.     

A detailed analysis of cross-phase modulation effects on OOK and dpsk optical WDM transmission systems in the presence of GVD,SPM, and ASE noise

A performance analysis is carried out to evaluate the effect of cross-phase modulation (XPM) on a dispersion-managed 20 Gb/s optical wavelength-division multiplexing (WDM) transmission system using either the on-off keying (OOK) or the different-phase-shifting keying (DPSK) modulation, in the presence of the group-velocity dispersion (GVD), self-phase modulation (SPM), and amplified spontaneous emission (ASE). It is found that to achieve a bit error rate (BER) of 10⁻⁹ at a distance of 160 km, a 1.0 dB XPM power penalty is incurred for input channel power of 3 dBm in the OOK transmission and 7 dBm in the DPSK transmission. The power penalty increases with input channel powers and is inversely proportional and exhibits oscillations with respect to the channel separation. The oscillation is evenly spaced for the DPSK but not for the OOK and suggests the presence of optimum separation values. The XPM penalty decreases when a high dispersion fiber is used and increases linearly with increasing dispersion slope. Small residual dispersion can reduce the penalty of nonlinear effects.     

偏分复用系统中偏振模色散补偿与偏分解复用一体化方案

本文建立了偏分复用系统中偏振模色散与信号偏振态变化引起信道串扰的数学模型, 分析了偏振模色散对偏分复用信道射频功率的影响, 并提出了适用于偏分复用系统的光域偏振模色散补偿与偏分解复用同时进行的方案: 用信道的射频功率作为反馈控制信号, 监测链路中偏振模色散和偏振态变化引起的信道串扰的大小, 用改进的粒子群优化算法对偏振控制器进行自适应控制, 同时完成偏振模色散补偿与偏分解复用. 在112 Gb/s偏分复用-差分正交相移键控(PDM-DQPSK)传输系统中仿真验证了该方案的有效性. 结果表明该方案可以使112 Gb/s-PDM-DQPSK传输系统完成自适应偏分解复用的同时, 在1 dB的光信噪比代价下, 使系统对偏振模色散的容忍度提高20 ps. 关键词： 偏分复用系统 信道串扰 偏振模色散 偏分解复用     

XPM-induced crosstalk with higher order dispersion in SCM-WDM optical transmission link

In this paper, the XPM-induced crosstalk has been evaluated with higher order dispersion in SCM-WDM optical transmission link at different modulation frequencies. It has been observed that there is exponent increase in XPM-induced crosstalk with the increase in modulation frequency from 0 to 3 GHz. The impact of 3OD, 4OD and 5OD is small as compared to 2OD but still contributes when the combined terms are considered. The combined effect of second, third, fourth and fifth-order dispersion parameters is that the induced crosstalk introduced by XPM increases.     

Experimental and Theoretical Investigation of Nonlinear-Crosstalk in SCM-WDM CATV Systems

The generation of crosstalk in wavelength division multiplexed cable television (WDM-CATV) networks due to fiber-induced nonlinearities is studied, both theoretically and experimentally. For the first time, to our knowledge, the contribution of electrostriction to the generated crosstalk level in such systems is included in an analytical model. The critical parameters of the system are defined and analyzed and their impact on the formation of the nonlinear crosstalk is examined. The comparison between the theoretical results and the experimental data reveals very good agreement and has allowed the optimization of the performance of the system in terms of its critical parameters. For fixed channel numbers, twofold reduction in channel spacing increases the crosstalk by 3 dB/ch. For fixed channel spacing, doubling the number of channels results in 1 dB/ch crosstalk increase.     

Simulation of DWDM signals using optimum span scheme with cascaded optimized semiconductor optical amplifiers

We numerically simulated the ten channels at 10 Gb/s dense wavelength division multiplexing (DWDM) transmission faithfully over 17,227 km using 70 km span of single mode fiber (SMF) and dispersion compensating fiber (DCF) using optimum span scheme at channel spacing 20 GHz. For this purpose, inline optimized semiconductor optical amplifiers (SOAs) and DPSK format are used. We optimized the SOA parameters for inline amplifier with minimum crosstalk and amplified spontaneous emission noise with sufficient gain at bias current 400 mA. For this bias current, constant gain 36.5 dB is obtained up to saturation power 21.35 mW. We have also optimized the optical phase modulator bandwidth for 400 mA current which is around 5.5 GHz with crosstalk −14.2 dB between two channels at spacing 20 GHz.We show the 10×10 Gb/s transmission over 70 km distance with inline amplifier has good signal power received as compared to without amplifier, even at equal quality factor. We further investigated the optimum span scheme for 5670 km transmission distance for 10×10 Gb/s with channel spacing 20 at 5.5 GHz optical phase modulator bandwidth. As we increase the transmission distance up to 17,227 km, there is increase in power penalty with reasonable quality.The impact of optical power received and Q factor at 5670 and 17,227 km transmission distance for different span schemes for all channels has been illustrated. For launched optical power less than saturation, all channels are obtained at bit error rate floor of 10⁻¹⁰.     

Transmission performance of the SCM label in optical label switching networks

We have investigated the transmission performance of the label signal in the optical double sideband subcarrier multiplexing (DSB-SCM) label switching link and clarified that the degradation of the label signal results from the fiber chromatic dispersion and the incomplete filtering out of the payload carrier. Our theoretical results show that the DSB-SCM label can immune the fading effect, and the degradation mainly results from the crosstalk from the payload and the time shift of the code edge. The deep suppression of the optical carriers at the receiver can eliminate the crosstalk. The time shift of the code edges leads to the eye closure of the label codes and is independent of the code rate, but it does not degrade the label code with a low bit rate greatly, although it is serious for the label with a high bit rate and ultimately limits the transmission distance of the label. The simulation results validate our analysis very well. As we theoretically predict that the single sideband (SSB)-SCM can eliminate the time shift of the code edges and extend the transmission distance of the label signal.