模分复用系统中的模式耦合和差分模式群时延对信号传输的影响, 需在接收端进行均衡补偿以实现信号可靠传输。与时域均衡相比, 频域均衡可有效降低DSP复杂度。基于频域盲均衡算法FD-CMA(frequency-domain constant modulus algorithm)和FD-MMA(frequency-domain multimodulus algorithm)在2×56 Gb/s 16 QAM模分复用系统中进行仿真对比。结果表明, 从星座图和误码性能角度来讲, FD-MMA对非常数模信号的均衡性能优于FD-CMA。在误比特率为10-3处, FD-MMA较FD-CMA有2.8 dB光信噪比的提升。

基于异步延时采样结合神经网络的方法, 提出一种利用广义回归神经网络(GRNN)对光信噪比(OSNR)和色散(CD)的监测方法, 主要在40 Gbit/s 16QAM通信系统以及非线性信道环境中, 通过异步采样方法提取特征量, 用GRNN实现OSNR、CD的监测。GRNN方法不仅可以实现OSNR、CD的监测, 与其他神经网络方法相比还具有参数少、算法效率高、易于优化的特点。

在相干光通信系统中, 激光器相位噪声导致信号在复平面发生旋转, 因此在接收端需要对信号进行载波相位估计和恢复。文中主要对当前载波相位估计算法特性进行比较研究。介绍了两种经典算法Viterbi&Viterbi算法和盲相位搜索(BPS)算法的基本原理, 总结了六种二阶级联相位噪声估计算法。比较八种载波相位估计算法的硬件复杂度及线宽容忍度, 并评估了这八种载波相位估计算法在16QAM系统中的性能。

数值仿真研究了双曲正割、高斯(m=1)、超高斯脉冲(m=5)形皮秒脉冲泵浦在高非线性光纤正常色散区中时频域演化特性.计算结果表明,在峰值功率、泵浦光纤参数相同的条件下,泵浦脉冲前(后)沿陡峭程度影响频谱展宽宽度,脉冲前后沿越陡峭,生成的超连续谱带宽越宽;脉冲前(后)沿的拖尾部影响展宽频谱的平坦性,脉冲前后沿拖尾越小,生成的超连续谱频带平坦度越高.泵浦脉冲中是否含有啁啾对生成的超连续谱的带宽和平坦性影响微弱.脉冲前(后)沿拖尾小或者陡峭的脉冲在高非线性光纤正常色散区可以产生带宽平坦的超连续谱.

A cost-effective ultra-dense wavelength-division-multiplexed passive optical network (UD-WDM PON) with speed of 12.5 Gbit/s and channel spacing of 12.5 GHz is proposed and demonstrated. The distributed feedback (DFB) lasers modulated in 4-level pulse amplitude modulation (4-PAM) format are used for downstream links, and the reflective semiconductor optical amplifiers (RSOAs) together with an optical frequency comb modulated in quadrature phase shift keying (QPSK) format are used for upstream links. We can achieve the error-free transmission of the upstream signals with speed of 12.5 Gbit/s even after 20 km single-mode fiber (SMF). The power penalty obtained by using the frequency comb generator instead of a tunable laser is around 0.5 dB. By using 11 DFB lasers and a set of intensity and phase modulators, it is possible to provide the seed light for 297 optical network units (ONUs) within the C-band.

A novel approach for the implementation of microwave photonic filter with positive and negative coefficients based on an unbalanced Mach-Zehnder modulator (MZM) is proposed. In the proposed filter, a microwave signal to be filtered is applied to an unbalanced MZM. Thanks to the unbalance between the two arms of the modulator, a π phase shift is obtained by adjusting the wavelength interval between the adjacent wavelengths, which leads to the generation of the positive and negative coefficients. The theoretical fundamentals of the design are described, which show that the required unbalanced MZM in the scheme can be well fabricated by the current technology, and the required other components, including the wavelength multiplexer, are also commercially available devices. An eight-tap microwave photonic filter with positive and negative coefficients is demonstrated. The tunability and reconfigurability of the eight-tap microwave photonic filter are also investigated to verify our approach.

An improved multiplier-free feed-forward carrier phase estimation algorithm is proposed for dual-polarization quadrature- phase-shift-keying (DP-QPSK) with coherent detection. The bit error rate (BER) performance, block length effect and linewidth tolerance of the proposed algorithm are evaluated for a 112 Gbit/s DP-QPSK system. A linewidth symbol duration product of 2.9×10^-4is demonstrated for 1 dB optical signal-to-noise-ratio (OSNR) penalty at BER of 10^-3for the proposed algorithm. The hardware complexity of the proposed multiplier-free algorithm is demonstrated to be much lower than that of the 4th power algorithm.