四波混频对DWDM系统的影响

光纤中的四波混频 ( FWM)效应对密度集波分复用 ( DWDM)系统造成了较大的不利影响 ,必须采取相应的措施予以克服。首先分析 FWM产生的机理和影响混频效率的主要因素 ,然后研究 FWM对 DWDM系统性能的影响 ,最后提出了几种克服 FWM对 DWDM系统性能影响的方法。     

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     

Pump-pump four-wave mixing in distributed Raman amplified systems

This paper describes the four-wave mixing (FWM) interaction of several Raman pumps and its effect on optical-signal-to-noise ratio and Raman gain. In this paper, the modeling of the combined Raman and FWM effects is explained and is used for the impairment investigation. We compare the relative importance of amplifier parameters. In particular, the paper shows how wide pumps increase the regions of forbidden zero-dispersion wavelength and increase the penalty regions in the signal band. Fiber parameters beyond zero-dispersion wavelength (dispersion slope, effective area, and Rayleigh scattering) are also investigated but show little impact. Finally, the paper considers nonuniform spans and shows that the use of short cables makes pump-pump FWM a likely problem.     

Intrachannel four-wave mixing in dispersion managed RZ systems

We model the interaction of three consecutive pulses in a dispersion managed transmission system, and obtain an analytical expression for the energy exchange. The results show that interaction can be suppressed using unequally spaced pulses, which has been verified by the computer simulations. The central pulse pumps energy to the adjacent pulses if the phase shift is zero, and the energy exchange process is reversed if the central pulse has a phase shift of π/2     

Polarization effect on four-wave mixing efficiency in a single-modefiber

Four-wave mixing in a single-mode fiber is studied for general polarization states in input lights. A theory is developed for fiber four-wave mixing where the polarization states of input light are various and they change randomly when propagating through a fiber line. The results show that intensity beating between the propagating lights plays an important role in four-wave mixing efficiency in a fiber. Experimental results support the theoretical treatment     

Regenerative properties of a pump-modulated four-wave mixing scheme in dispersion-shifted fibers

A new scheme for all-optical signal reshaping is proposed. It is shown that proper adjustment of the operating conditions of a wavelength converter based on four-wave mixing (FWM) in dispersion-shifted fiber (DSF) results in significant extinction ratio enhancement and noise suppression of the converted signal. The key issue in the proposed idea is the application of the modulation bitstream on the input pump wave. Detailed numerical simulation shows that it is possible to achieve a wavelength-converted output with extinction ratio of 20 dB when the extinction ratio of the input signal is 10.5 dB, while at the same time, the improvement in the Q-factor is almost 6 (from 6.5 at the input, it becomes more than 12 at the output). The theoretical predictions have been experimentally confirmed by measuring the transfer function of the FWM in a 17-km-long DSF under different operating conditions. The obtained results are in a very good agreement with those predicted theoretically.     

All-optical signal reshaping by means of four-wave mixing inoptical fibers

It is experimentally demonstrated that the four-wave mixing (FWM) effect in an optical fiber can be exploited to achieve all-optical reshaping. The injection of a signal and a strong continuous-wave (CW) pump into a common dispersion-shifted fiber results in several wavelength-converted replicas of the signal. These spectral components exhibit various reshaping behaviors. Selecting low-order FWM waves, we observe a sinusoidal-like transfer function. However, unlike other reshaping devices, a step-like transfer function is obtained for higher order mixing products. A significant noise compression is observed at the converted output, starting from an input noisy nonreturn-to-zero (NRZ) signal stream     

Fiber four-wave mixing in multi-amplifier systems with nonuniformchromatic dispersion

Fiber fiber-wave mixing (FWM) is studied for multichannel multi-amplifier systems composed of short fibers with different zero-dispersion wavelength. An analytical expression describing FWM in these systems is derived. Using the expression, crosstalk is calculated for various combinations of fiber lengths, which are selected according to a random function, and allowable fiber input power is evaluated. The results show that the allowable input power for nonuniform dispersion is larger than that for uniform dispersion by several dB, depending on system conditions     

Statistical property of intra-channel four-wave mixing in RZ-DPSK transmission systems

The statistical property of intra-channel four-wave-mixing (IFWM) is studied numerically for return-to-zero differential-phase-shift keying transmission. The distributions of IFWM-induced pulse power and phase fluctuations depend on the relative strength of pulse broadening and nonlinear interactions, which can be characterized with a dimensionless parameter. We thus offer a general criterion to understand the stochastic nature of IFWM effect.     

Influence of fiber four-wave mixing on multichannel FSK directdetection transmission systems

The influence of fiber four-wave mixing on multichannel FSK direct detection transmission is investigated. A theoretical study is presented for evaluating error rate performance when four-wave mixing lights are overlapped onto a signal channel. Experiments are carried out to examine the theoretical treatment. Based on these results, allowable fiber input power is estimated     

Transient four-wave mixing and real time holography in atomic systems

The problem of transient four-wave mixing with noncoincident optical pulses is analyzed using the formalism of the time evolution and the density matrix operators. The results are relevant to problems involving real time holography and wave conjugation. The treatment establishes a bridge between the conventional formalisms of nonlinear optics and of photon echoes.     

基于SOA四波混频效应的慢光特性研究

根据行波SOA的四波混频效应,讨论了不同参数条件下的慢光时延特性。采用SOA分段模型,定量分析了光时延量与偏置电流、频率失谐、泵浦光功率的关系,以及泵浦光功率、载流子寿命的改变对工作带宽的影响。结果表明:可以通过调节频率失谐、偏置电流等参数对光时延量进行控制,增加泵浦光功率或抑制载流子寿命均可提高工作带宽。     

偏振对DWDM系统内四波混频噪声的研究

使用了一种有效的能对四波混频(FWM)噪声对DWDM系统性能影响程度进行评估的仿真模型.通过对使用在线色散补偿与后补偿相结合的新型色散管理光纤链路进行仿真,看出每个周期跨距内的残余色散对FWM噪声有一定抑制作用,适当提高每个周期跨距内的残余色散有助于提高总的非线性容限和系统的整体性能.     

Reduction of four-wave mixing crosstalk in WDM systems usingunequally spaced channels

Crosstalk due to four-wave mixing (FWM) is the dominant nonlinear effect in long-haul multichannel optical communication systems employing dispersion-shifted fiber. A technique to design the channel frequency allocation in order to minimize the crosstalk due to FWM is presented. It is shown that suitable unequal channel separations can be found for which no four-wave mixing product term is superimposed on any of the transmitted channels. This is obtained at the expense of some expansion of the system bandwidth. Simulations are presented to show the effectiveness of this technique in a 10-channel, 10-Gb/s per channel, system     

单缀饰四波混频缀饰效应的频率控制

主要研究了单缀饰四波混频信号的频率控制。首先,通过扫描探测场失谐及扫描缀饰场失谐两种方法,分别获得四波混频信号的Autler-Townes分裂和增强抑制现象;接着,在零失谐、小失谐和大失谐三个位置处,对比了两种扫描方法;在扫描缀饰场失谐时,观察到四波混频信号从纯抑制到半增强半抑制的转化过程;最后,通过对比发现,当探测场失谐越大时,缀饰场的缀饰效应就越弱。研究结果表明,相比于扫描探测场失谐,扫描缀饰场失谐的方法能实现对缀饰效应的直接测量。     

Effect of four-wave mixing on WDM optical systems: a statistical analysis

The dense wavelength-division-multiplexed system design requires an accurate knowledge of the four-wave mixing (FWM), which gives rise to intermodulation effects, especially when using very low-dispersion fibers. In this letter, a statistical analysis is presented that takes into account both the effect on the FWM intermodulation products due to dispersive propagation, and the statistics of such intermodulation terms, which must be considered as random processes. In particular, the autocorrelation function of the FWM process is calculated for the independent wavelength-division-multiplexing optical channel.     

Stimulated Raman effect and four-wave mixing in a hollow waveguide

A theoretical and experimental investigation of stimulated Raman scattering and four-wave mixing in a gas-filled hollow waveguide was performed. The four-wave mixing processes, specifically the generation of the third Stokes component at ω₃ when ω₃ =2ω₂-ω₁, show a strong resonance-like behavior as a function of wavelength. These resonances are caused by the phase matching required for efficient four-wave mixing, because the hollow waveguide supports only certain propagation directions leading to the development of waveguide modes. The theoretical results are compared with experimental data for TEM₀₀ and TEM₁₀ fundamental dye-laser beams generating third Stokes wavelengths between 2.6 and 7.5 μm     

The influence of velocity-changing collisions on resonantdegenerate four-wave mixing

The phase-conjugate signal observed in resonant degenerate four-wave mixing on the 6³P₂ to 7³ S₁ transition of atomic mercury in a Hg-Ar discharge is investigated. At a fixed argon pressure the variation of the signal with pump powers is explained by a model that includes the effects of velocity-changing collisions (VCCs). As the argon pressure was varied from 0 to 1 torr an increase in the phase conjugate signal was observed and is ascribed to a change in the discharge dynamics with argon pressure and to the influence of VCCs. To further clarify the role of collisions and optical pumping, degenerate four-wave mixing spectra are examined as a function of pump power. Line shapes are briefly discussed     

Photonic generation of triangular and rectangular waveforms based on four-wave mixing effect

A photonic approach that can generate triangular and rectangular waveforms is proposed. A dual-electrode Mach-Zehnder modulator(De-MZM) is used to fulfill the external optical carrier suppression(OCS) modulation of a continuous wave(CW). The follow-up four-wave mixing(FWM) in a semiconductor optical amplifier(SOA) makes four primary sidebands exist in the spectrum. Then filtering and optical carrier recovery techniques are used to construct the spectrum aligning with that of a triangular/rectang...     

布里渊增强四波混频研究的进展

当一个布里渊频移的信号在布里渊激活介质中与两束相反方向传播的强泵浦光相互作用时,将产生一个随时间指数增长的共轭场,直到它抽空泵浦场,并且由此产生很高的反射率(大于106)。这项技术可用于共轭微弱信号(小于10-13J),或者可以用于把大部分泵浦能量转移到共轭光,对此技术作了回顾。