DWDM系统啁啾高斯脉冲简并四波混频噪声标准差的计算

Calculation of degenerate four-wave-mixing noise for chirped Gaussian pulse in dense-wavelength-division-multiplexed system

假定入射脉冲为啁啾高斯脉冲,考虑到各信道内的比特模式及比特序列初始相位的随机性,得到此种情况下的强度调制直接检测(IM/DD)密集波分复用系统(DWDM)简并四波混频噪声标准差的半解析理论计算模型,这个理论模型同时考虑到各信道间的脉冲走离效应的影响,计算结果表明:除了群速度色散、信道间隔等是影响此种标准差的重要因素外,当高斯脉冲有较小的初始脉宽时,各信道比特序列的相对初始时延、初始啁啾参量都是重要的影响因素;初始脉宽较小时,色散效应导致的脉宽随距离的变化对这种标准差值的影响不能忽略。

The launched pulses for dense wavelength-division-multiplexing （DWDM） system with intensity modulated and direct-detection （ IM/DD ） scheme are assumed to be chirped Gaussian pulses. The pattern and initial phase of bit sequence in each channel are random. A statistical method is used to analyze these random quantities and a semi-analytic calculation model applied to evaluate the variance of degenerate four-wave-mixing （FWM） noise is obtained. The model also accounts for walk-off effect between channels. The results of calculation show that, to the value of deviation of degenerate FWM noise of chirped Gaussian pulse, not only the group velocity and channel separation are important, but also the initial delay of bit sequence of each channel and initial chirp of pulse are important in the case of small values of launched pulse width. It is also shown that, when the width of launched pulse is small, the change of pulse width with distance due to dispersion effect must be considered to avoid relative large error.