We demonstrate a new scheme for generation of optical frequency comb (OFC) based on cascade modulators, 23 comb lines within 0.5 dB spectral power variation are obtained. An optical finite impulse response (FIR) filter is introduced for suppression of amplified spontaneous emission noise. It is shown that carrier-to-noise-ratio of the OFC generated by this scheme can be as high as 38.8 dB with 12 dB improvement by using a 16-tap FIR filter, and the error vector magnitude performances of loaded Nyquist-16 quadrature amplitude -modulation signal is improved from 14.20% to 7.44%.

为抑制循环频移器（RFS）中IQ调制器的非线性引起的三阶串扰，提高多载波光源输出的平坦度和载噪比，提出了基于线性IQ调制器(LIQM)的循环频移器结构（LIQM-RFS）的多载波产生方案。理论分析得出线性IQ调制器在有效抑制三阶串扰的情况下，对射频信号驱动电压的选择范围是IQ调制器的两倍，特别是能够在一阶信号转换效率较高的范围内实现对三阶串扰的抑制。利用这一特性，基于LIQM-RFS的多载波发生器在保证输出子载波平坦度的同时可以降低所需的掺铒光纤放大器(EDFA)增益，从而降低光纤放大器引起的自发辐射噪声的功率，提高载噪比。仿真结果表明基于LIQM-RFS的多载波发生器输出载波的载噪比较传统RFS提高约9 dB，同时可以保证约2.95 dB的平坦度。

提出了改进的利用信号功率谱的自相关函数(ACSPW)监测相干系统中色散(CD)的方案。在链路中加入更大的色散值来克服传统使用ACSPW监测CD方法的限制。扩大监测范围的方式为人为添加已知的较大CD值，对接收到的信号使用有限脉冲反应滤波器的估计阶段，移动功率谱自相关函数到可以测量的范围内，最后减去已知的添加的CD值即为估计值。此方法基本上不受放大的自发辐射噪声、脉冲的形状和偏振模色散的影响。监测结果平均误差为127 ps/nm。

The laser source is an important element whose properties have influence on the output performance of single sideband (SSB) optical comb based on recirculating frequency shifter (RFS). The theoretical and experimental results show that the tone-to-noise ratio (TNR), flatness, and stability of optical comb improve using laser source with narrower linewidth. In order to obtain the optical comb with TNR larger than 42 dB and degree of stability (DOS) smaller than -6.7 dB, external cavity laser (ECL) with linewidth from 100 kHz to 1 MHz is a trade-off choice.