光纤中的四波混频及其受色散的影响

讨论了四波混频的效率及色散对四波混频的影响，并推导了四波混频光的效率公式。另外，在光纤线路中由于每段光纤的零色散波长略有不同，四波混频的发生与有均匀零色散波长光纤中的不同，本文对这种情况下的四波混频也进行了分析研究。     

波分复用系统中四波混频引入光信噪比的恶化及其抑制

本文对陆上级联接掺铒光纤放大器（ＥＤＰＡ）波分复用光纤通信系统中国波混频所造成的各个光信道光信噪比的恶化提出了一套计算方法，并结合常规单模光纤及一种特殊设计的色散位移光纤进行了分析计算。结果表明：在四波混频所引入的光信噪比恶化中，因新生频率分量导致的噪声增加一般远大于光信号功率的减弱。不等信道间隔划分能有效地避免四波混频的影响，而光滤波器的带宽应在允许范围内尽量压窄。对采用色散补偿技术的级联ＥＤＦＡ波分复用系统，在同一光中继段内，使常规单模光纤置于特殊设计的色散位移光纤之前，能进一步减少四波混频带来的光信噪比的恶化。     

四波混频和级联四波混频效应产生的连续光频率梳

针对产生光频率梳需要锁模激光种子源的难题,创新性提出了用连续光源产生光频率梳,应用色散平坦高非线性光纤解决了宽光谱范围四波混频和级联四波混频效应的相位失配问题。通过实验展示了近40 nm带宽的光频率梳的形成,光频率梳由低功耗,低成本,连续波种子（法布里-珀罗激光器）生成,无需脉冲激光源。连续光频率梳是由在420 m零色散色散平坦高非线性光纤中的四波混频和级联四波混频效应产生的,频谱带宽扩展了近10倍,频率梳的线宽为4.3 MHz。     

WDM+EDFA+DCF光纤传输系统中色散补偿方案的分析

由于在ＷＤＭ＋ＥＤＦＡ光纤传输系统中使用常规单模光纤（ＳＭＦ）在１５５０ｎｍ窗口的大色散限制了传输距离,采用色散补偿光纤（ＤＣＦ）进行色散补偿是上前一种较为理想的方法。本文基于光纤ＷＤＭ＋ＥＤＦＡ＋ＤＣＦ的长距离传输系统,讨论了ＤＣＦ色散补偿对光纤非线性效应交叉相位调制和四波混频（ＦＷＭ）的影响,提出了采用ＤＣＦ集总、后置、非完全补偿的色散补偿方案,这种方案可合系统具有更佳的传输性能。     

非线性双折射阶跃光纤中的极化调制不稳定性

利用光脉冲在光纤中传播时所遵守的相干非线性薛定谔耦合方程,研究了线偏振光在 弱双折射阶跃光纤中的传输特性。结果表明,由于线性双折射和色散的相互作用,导致光的偏振态发生变化,产生交叉相位调制(XPM) ,从而导致相位匹配参量的四波混频。这一过程不仅在反常色散区产生,在正常色散区也能产生,并且当表征距离的级数m发生变化时,也随之发生变化。     

波分复用系统的四波混频特性研究

本文对波分复用（WDM）光纤通信系统中的四波混频（FWM）特性进行了研究，得到了WDM可用于由多段不同长度，不同色散值的光纤组成的多级放大WDM系统FWM效应的计算方法，进而分析了单级、多级放大和色散补偿这3种特例的FWM特性，研究结果表明，标准单模光纤与高负色散值色散移位光纤的组合可以有效地抑制FWM混频效应。     

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.     

非线性双折射色散缓变光纤中极化调制不稳定性

利用光脉冲在光纤申传播时所遵守的相干非线性薛定谔耦合方程，研究了线偏振光在双折射色散缓变光纤申的传输特性．结果表明，线性双折射、非线性效应和色散的相互作用，使光的偏振状态发生变化，产生交叉相位调制(XPM)，从而导致相位匹配参量的四波混频．这一过程不仅在反常色散区产生，在正常色散区也能产生，并且当传输距离发生变化时，也随之发生变化．     

随机相位误差对光纤光栅的影响

利用耦合波理论,分析了由于相位掩模板的接缝误差及光纤光栅写入过程中引入的相位误差对光纤光栅特性的影响.通过数值模拟,得到了随机相位误差对不同啁啾量的线性啁啾光纤光栅的影响.讨论了在通信系统中用光纤光栅进行色散补偿时,应该如何选取光纤光栅的啁啾量.     

常规DSF光纤参变放大器的带宽拓宽研究

为了拓宽常规色散位移光纤(DSF)型双抽运光纤参变放大器(FOPA)的放大带宽,提出了用DSF和单模光纤(SMF)级联来构造周期色散补偿双抽运FOPA的思想。利用SMF正的二阶色散以减小DSF负的四阶色散引起的相位失配,从而达到有效拓宽FOPA放大带宽的目的。结合四波混频耦合方程对该双抽运FOPA进行仿真研究,得到拓宽为69nm的放大带宽的结果。结果表明,光纤长度一定时,采用给出的最佳补偿光纤长度进行色散补偿,可有效减小因DSF四阶色散引起的相位偏移,进而拓宽放大带宽;分多段级联进行色散补偿时,可进一步拓展放大带宽。     

Four-wave mixing in an optical fiber in the zero-dispersionwavelength region

Fiber four-wave mixing (FWM) in the zero-dispersion wavelength region is described. The phase-matching characteristics are studied in the wavelength region where the first-order chromatic dispersion is zero. The results show that the phase-matching condition is satisfied and FWM light is efficiently generated at particular combinations of input light wavelengths. It is also shown that the deviation of the zero-dispersion wavelength along the fiber length plays an important role in FWM behavior     

Nonlinear enhancement and optimization of phase-conjugationefficiency in optical fibers

Analyzes the optimal generation efficiency of a phase conjugate wave by means of four-wave mixing in optical fibers. The author uses an exact model including linear absorption and pump depletion. It is shown that the nonlinear detuning of the phase matching condition may enhance the conversion efficiency if the pump is in the anomalous chromatic dispersion region and the input signal is much less intense than the pump     

Measuring the longitudinal distribution of four-wave mixingefficiency in dispersion-shifted fibers

We measured and analysed four-wave mixing (FWM) efficiency and fluctuation along the actual dispersion-shifted fibers (DSF's). In the short, 1.1-km DSF, our results agreed with theory, and we also obtained zero-dispersion wavelength λ₀, zero-dispersion slope dD/dλ, and nonlinear refractive index n₂ simultaneously. In the long, 23-km, DSF, a high FWM efficiency was observed in the wide wavelength region, due to the longitudinal zero-dispersion wavelength distribution. The fluctuation range was about 3.5 nm and the maximum slope about 1.1 km/nm     

Experimental study on channel crosstalk due to fiber four-wavemixing around the zero-dispersion wavelength

Channel crosstalk due to fiber four-wave mixing (FWM) in multichannel systems operated around the zero-dispersion wavelength is experimentally studied. After determining the wavelength at which FWM light is most efficiently generated, the FWM efficiency is measured for possible frequency combinations which generate FWM light at that wavelength. Using these data, FWM crosstalk in multiwavelength systems is evaluated. The results show that actual crosstalk, is less than the value estimated by the theoretical model assuming the uniformly distributed chromatic dispersion for 80-km-long fibers. It is concluded that the theoretical model can be applied to system design dealing with the worst condition     

Effects of Frequency Allocations and Zero-Dispersion Frequencies on FDM Lightwave Transmission Systems

In long-haul frequency-division-multiplexing lightwave transmission systems, transmission characteristics are degraded by four-wave mixing (FWM) generated in optical fibers. To overcome this problem, modified repeated unequally spaced (RUS) allocations such as equally spaced RUS (ERUS) and unequally spaced RUS (URUS) allocations have already been examined. In addition, it has been shown that FWM noises decrease by separating signal frequencies and a zero-dispersion frequency in equally spaced (ES) allocations. In this paper, ES, ERUS, and URUS allocations are studied from the viewpoint of the position of the zero-dispersion frequency relative to the signal frequencies. It is revealed that FWM noises are reduced in ES, ERUS, and URUS, with an increase in the separation between the signal frequencies and the zero-dispersion frequency, and FWM noises in ERUS and URUS are much lower than FWM noises in ES.     

Effect of fiber nonlinearity on long-distance transmission

The effect of the weak refractive-index nonlinearity of optical fibers on pulse shape is investigated using computer simulations of long-distance transmission. Fiber losses are canceled by periodically spaced optical amplifiers whose spontaneous emission noise is, however, not included in the simulations. The analysis is confined to normal pulses and does not consider solitons. Several conclusions are drawn. (1) If wavelength division multiplexing (WDM) of two channels is used in a uniform fiber without dispersion fluctuations, catastrophic buildup of four-wave mixing occurs if one primary channel is located at the zero-dispersion wavelength. (2) If two pulses with different carrier frequencies collide in a uniform fiber with no gain or loss discontinuities, their four-wave mixing products reach a peak during complete pulse overlap, but this spurious power dies away as the pulses separate. (3) Two-channel WDM transmission of light modulated in amplitude-shift keying format appears feasible at 2.5 GB/s over distances of 7500 km     

Influence of phase mismatch on a spectral inverter based onfour-wave mixing in dispersion-shifted fiber at 10 Gb/s

We investigate the influence of phase mismatch on the performance of a spectral inverter based on four-wave mixing in a commercial dispersion-shifted fiber. The inverter operates at 10 Gb/s. When the pump wave is tuned ±0.3 mn around the zero-dispersion wavelength of the fiber, the power penalty at 10^-9 bit-error rate remains within the range of 1-2 dB, although the conjugate power is reduced considerably by almost 6 dB. A numerical calculation of the inverter's efficiency is also presented, which takes into account longitudinal variation of the zero-dispersion wavelength along the fiber     

Gain enhancement in cascaded fiber parametric amplifier withquasi-phase matching: theory and experiment

We report a novel gain enhancement scheme for fiber-optic parametric amplifiers utilizing cascaded amplification and quasi-phase matching (QPM). The theory and method of QPM for four-wave mixing (FWM) are developed for the first time to our knowledge. In experimental implementations of the theory, we achieve >12 dB gain improvement in a three-stage dispersion-shifted (DS) fiber parametric amplifier. A 16-dB overall gain is obtained with 11 nm separation between zero-dispersion wavelength and pump wavelength. The experimental results show good agreement with theory and simulations. The influence of QPM on spectral characteristics of parametric gain is investigated with numerical simulations     

Detailed numerical analysis of a four-wave mixing in dispersion-shifted fiber based all-optical wavelength converter of 10 Gb/s single sideband optical signal

We analyze the Q factor and the conversion efficiency of all-optical wavelength converter based on four-wave mixing in dispersion-shifted fibers at 10 Gb/s employing single sideband signal. We find that the Q factor of the converted signal is always higher for upper-single sideband signal with upward conversion in wavelength and for lower-single sideband signal with downward conversion. The four-wave mixing efficiency is higher when the pump wavelength is deviated positively relative to the fiber zero-dispersion wavelength. The used of low dispersion slope allows broad bandwidth and broad dynamic range of pump wavelength. From this study we depict the working characteristics of an all-optical wavelength converter for upper and lower single side band signals, providing guidelines to the utilization of these very promising technologies in the implementation of the future high bit rate all-optical networks.     

Phase conjugation by four-wave mixing in single-mode fibers

We present an exact solution to the coupled-mode equations, governing four-wave mixing in single-mode fibers, under the perfect phase-matching condition. The solution accounts for pump depletion and fiber absorption. Optimum length of fiber is derived and phase conjugation efficiency is calculated and discussed. The calculated results are in good agreement with the reported experimental results