Effect of four-wave mixing in WDM optical fibre systems

Wavelength division multiplexing (WDM) can both significantly enhance transmission capacity and provide more flexibility in optical network design. Through the use of erbium-doped fibre amplifiers (EDFAs), it is possible to build long-distance transparent optical transmission links without electrical regenerators. In such systems, fibre nonlinearities are likely to impose a transmission limit due to increased total interaction length. There are a number of optical nonlinear effects in optical fibres, such as stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), carrier-induced phase modulation and four-wave mixing (FWM). Out of these SRS and FWM are the dominant effects. In this paper, an algorithm has been suggested to study the effect of FWM in the total system noise considering the combined effect of SRS and FWM in the presence of amplified spontaneous noise (ASE). It has been found from the study that to maximize the signal-to-noise ratio of the transmitted signal in a WDM system FWM noise needs to be reduced as this is the dominant noise factor.     

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.     

Impact of ASE noise in WDM systems

The small signal analysis method is presented for the discussion of amplified spontaneous emission (ASE) noise in dispersion and nonlinear transmission fibers in wavelength division multiplex (WDM) systems. Based on it, the complete ASE noise spectra (include the ASE noise, the ASE noise enhanced by parametric gain and the crosstalk caused by ASE noise and parametric gain) are described and the factors impacting on them are discussed. The crosstalk caused by ASE noise and parametric gain in single mode fibers, non-zero dispersion shift fibers and dispersion compensation fibers are analyzed. Taking into account the dispersion effect in the transmission fibers, the three types of ASE noise may decrease.     

Effect of pulse walk off and data formats on stimulated Raman scattering in fiber optic communication systems

A novel numerical method has been presented here which is capable of taking into account pulse walk off effect and different data formats such as non return to zero (NRZ), return to zero (RZ) and optical Manchester while evaluating the effect of stimulated Raman scattering (SRS) in dense wavelength division multiplexed (DWDM)-based fiber optic communication systems. Power tilt because of SRS effect in the DWDM systems has been calculated at different data rates and data formats.     

Performance analysis of optical WDM system based on unequal spaced channel allocation (USCA) scheme

Unequal spaced channel allocation (USCA) is a technique to reduce Four wave mixing (FWM). In this paper, system performance of 8 channel WDM system considering different optical transmitter formats (RZ, NRZ, Raised cosine and Gaussian) using USCA has been evaluated in terms of Q-factor. The simulation results reveal that four wave mixing is minimum for NRZ format. Also the effect of changing the laser power and increasing the bit rate has been observed.     

Performance evaluation of SCM-WDM communication in the presence of SRS induced crosstalk for different types of fiber

In this paper, the SRS-induced crosstalk has been evaluated in a SCM-WDM communication link at different modulation frequencies for various type of fibers. Results show that SRS-induced crosstalk dominates at low frequency. As the dispersion and effective area of fiber (A_eff) decreases, initially the crosstalk remains high and then it decreases with increase in modulation frequency. The present work shows that out of five different types of fibers, Standard Single Mode Fiber (SMF) has minimum crosstalk (−53 to −64 dB) and True Wave fiber (TW) has maximum crosstalk (−47 to −48 dB).     

Investigations on order and width of RZ super Gaussian pulse in different WDM systems at 40 Gb/s using dispersion compensating fibers

In optical wavelength division multiplexed (WDM) systems the dispersion management is a key issue. In optical systems a lot of research is going on to reduce dispersion by selecting proper dispersion compensating techniques and proper modulation format for input data. One way to reduce dispersion is by using dispersion compensating fibers in the WDM systems. This paper analyzes the use of RZ super Gaussian pulse inputs for different WDM systems i.e. for conventional, dense and ultra dense WDM systems employing dispersion compensating fibers. The pulse width and the order of the RZ super Gaussian pulse was varied to evaluate the performance at 40 Gb/s. The experiment showed that to get minimum BER, pulse width of 7.5 ps and 10 ps along with third-order RZ super Gaussian pulse were found suitable and recommended to be used.     

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.     

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.     

Analysis of Pulse Tolerance to Pump Depletion Induced Noise in DWDM Systems Using Distributed Fiber Raman Amplifiers

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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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Analysis of Pulse Tolerance to Pump Depletion Induced Noise in DWDM Systems Using Distributed Fiber Raman Amplifiers

In distributed optical fiber Raman amplifiers,instantaneous pump power depletion is related to patterns of input DWDM signals and results in extra optical noise and crosstalk.This noise has different effects on non-return-to-zero (NRZ) and return-to-zero (RZ) pulse forms.These phenomena are compared with present simulation results.     

组合光纤中受激拉曼散射和四波混频研究

在抽运光和耦合条件不变的情况下,研究了熔接组合的非零色散位移单模光纤(NZDSF)和标准单模光纤(SMF)中的受激拉曼散射(SRS)和四波混频(FWM)产生和传输特征。采用532 nm脉冲激光抽运NZDSF,从20 m处开始产生以LP₀₁模传输的SRS第一级Stokes光;紧接着在30 m处产生了FWM,SRS受到FWM抑制,传输模式逐渐转化为LP₁₁模;经过80 m处熔接点后,由于熔接处双锥光纤结构使光场模式互相干涉,光波模式恢复为LP₀₁模,FWM受到抑制。该现象和机理有利于抑制密集波分复用(DWDM)系统中光学非线性失真和促进光孤子通信系统的发展。     

光学频率梳非线性传输及其在相位噪声探测中的应用

光纤传递链路中相位噪声探测是基于光纤的精确射频标准传递系统中重要组成部分。为解决光纤链路相位噪声探测中节点反射干扰的问题, 本文基于广义非线性薛定谔方程, 理论上研究了窄带光学频率梳在色散位移光纤中的非线性光学传播特性。在理论分析的基础上, 结合密集波分复用架构, 提出了一种基于锁模光学频率梳进行光纤传递射频信号的相位噪声探测新技术, 克服了节点反射干扰, 给出了初步实验验证。     

WDM系统中ASE噪声的二阶色散效应

讨论了采用小信号分析法研究脉冲波在色散、非线性光纤中的传输时,放大的自发辐射(ASE)噪声作为功率调制项加入脉冲波的传输方程后所产生的效应.ASE噪声不仅被互相位调制不稳定增益所放大,还受二阶色散成分的影响.其传输函数为COS(1/2β2dzω2),这一函数不能通过色散补偿来消除,会削弱ASE噪声的影响.鉴于此,ASE...     

Performance of All-optical WDM Network in Presence of Four-wave Mixing, Optical Amplifier Noise, and Wavelength Converter Noise

The article investigates the effect of four-wave mixing (FWM), amplified spontaneous emission (ASE) noise, and wavelength converter noise on the performance of WDM all-optical networks. Analysis for the evaluation of probability of error has been carried out (a) when only thermal and shot noise are present; (b) when thermal, shot, FWM, and ASE noise are present; and (c) when thermal, shot, FWM, ASE, and wavelength converter noise are present. Numerical results are presented in the graphical forms for the practical values of parameters.