Performance analysis of dispersion compensating optical FIR filters designed using a quasi-analytic synthesis approach

In this paper we investigate the performance of a quasi-analytic synthesis approach for dispersion compensating optical finite impulse response filters. It is shown by eye opening penalty and optical signal to noise ratio penalty calculations that with this method the filters dispersion can be adjusted reliably and with low effort to compensate for a specific amount of residual chromatic dispersion in optical transmission systems. The maximum attainable dispersion is then only limited by the filter order and the free spectral range rather then by optimization problems within the filter design.     

光数字相干接收机中色散补偿模块设计与优化

在高速光纤通信数字相干接收系统中,色散补偿模块的结构和性能将直接决定其是否具有实用价值.设计了比传统的有限脉冲响应(FIR)滤波器结构简单的偶对称型FIR滤波器,并通过数值仿真分析了FIR滤波器长度选取对补偿效果的影响.研究结果表明,在接收端光信噪比(OSNR)代价不高于1 dB的情况下,FIR滤波器长度折衷选取为最大...     

偏振复用光纤通信系统色散均衡器及算法的研究

设计了一种适用于偏振复用相干解调光纤通信系统的色散均衡器,用于补偿信道传输的色散损伤。该均衡器采用半码元间隔的蝶形有限脉冲响应滤波器结构,与此结构配合的自适应算法分别采用最小均方算法和递归最小二乘算法。通过仿真实验,分析了两种算法对残留色度色散和偏振模色散的补偿容限。仿真结果表明,递归最小二乘算法的补偿效果优于最小均方算法,它可以同时补偿1760ps/nm的残留色度色散和104.9ps偏振模色散引起的差分群时延,比同等条件的最小均方算法提升性能2.23dB。     

光纤网络中的云数据并行调度

光纤网络的通信质量受到云数据调度均衡性影响很大,为了改善光纤网络通信质量,提高网络中云数据传输的吞吐量和保真率,通过云数据并行调度,实现云数据传输均衡,提出一种基于自适应判决反馈均衡的光纤网络云数据并行调度模型。构建光纤网络通信的传输信道模型,采用最小均方误差估计方法进行光纤网络的量化融合估计,运用匹配滤波检测器进行云数据中的干扰滤波处理,结合自适应判决反馈均衡方法进行信道均衡,在均衡的信道中对滤波输出的云数据进行并行调度和多线程输出调制。仿真结果表明,采用该方法进行光纤网络中的云数据并行调度的均衡性较好,输出数据的保真率较高,误码率较低,改善了光纤网络的整体性能。     

Robust Blind Adaptive Channel Equalization in Chaotic Communication Systems

Based on the bounded property and statistics of chaotic signal and the idea of set-membership identification, we propose a set-membership generalized least mean square （SM-GLMS） algorithm with variable step size for blind adaptive channel equalization in chaotic communication systems. The steady state performance of the proposed SM-GLMS algorithm is analysed, and comparison with an extended Kalman filter （EKF）-based adaptive algorithm and variable gain least mean square （VG-LMS） algorithm is performed for blind adaptive channel equalization. Simulations show that the proposed SM-GLMS algorithm can provide more significant steady state performance improvement than the EKF-based adaptive algorithm and VG-LMS algorithm.     

一种40Gb/s单信道光纤通信系统中的动态色度色散补偿

提出了一种用于40 Gb/s单信道光纤通信系统中的动态色度色散(CD)补偿技术。采用2×2光开关,色散补偿光纤(DCF)等器件构成可调节色度色散补偿器;提取中心频率为12GHz的窄带电功率信号作为反馈信号控制可调节色度色散补偿器,提取的窄带电功率值随系统中的累积色度色散值的增大而减小。实验证明,整个补偿系统的最长响应时间为0.7 s;补偿范围和补偿精度分别为81.55 ps/nm和5.28 ps/nm,通过增加光开关的数量和缩短每段色散补偿光纤的长度可以进一步提高补偿范围和精度。通过对比补偿前后系统的眼图可以看出:该系统能有效地补偿40 Gb/s光纤通信系统中动态变化的色度色散。     

混沌通信系统中非线性信道的自适应神经Legendre正交多项式均衡

针对混沌通信系统中非线性信道干扰问题，基于混沌信号重构理论和Legendre正交多项式结构，提出了一种自适应神经Legendre正交多项式信道均衡器，并给出相应的归一化最小均方算法. 仿真研究表明：所提出的自适应神经Legendre正交多项式信道均衡器能有效地消除线性和非线性信道干扰，均衡器输出信号能反映出混沌信号的特性，具有良好的抗干扰性能.该均衡器的结构简单，权系数参数较少，收敛稳定性较好. 关键词： Legendre 正交多项式 信道均衡 混沌吸引子 神经网络     

Nonlinear adaptive filters for high-speed LED based underwater visible light communication [Invited]

Underwater visible light communication(UVLC) is expected to act as an alternative candidate in nextgeneration underwater 5 G wireless optical communications. To realize high-speed UVLC, the challenge is the absorption, scattering, and turbulence of a water medium and the nonlinear response from imperfect optoelectronic devices that can bring large attenuations and a nonlinearity penalty. Nonlinear adaptive filters are commonly used in optical communication to compensate for nonlinearity. In this paper, we compare a recursive least square(RLS)-based Volterra filter, a least mean square(LMS)-based digital polynomial filter,and an LMS-based Volterra filter in terms of performance and computational complexity in underwater visible light communication. We experimentally demonstrate 2.325 Gb/s transmission through 1.2 m of water with a commercial blue light-emitting diode. Our goal is to assist the readers in refining the motivation, structure,performance, and cost of powerful nonlinear adaptive filters in the context of future underwater visible light communication in order to tap into hitherto unexplored applications and services.     

All-channel tunable optical dispersion compensator based on linear translation of a waveguide grating router

We propose and demonstrate a compact tunable optical dispersion compensation (TODC) device with a 100 GHz free spectral range capable of mitigating chromatic dispersion impairments. The TODC is based on longitudinal movement of a waveguide grating router, resulting in chromatic dispersion compensation of ±1000 ps/nm. We employed our TODC device for compensating 42.8 Gbit/sec differential phase-shifting keying signal, transmitted over 50 km fiber with a -2 dB power penalty at 10??.     

自适应中值-加权均值混合滤波器

为了去除图像中混入的脉冲噪声和高斯噪声,提出了一种基于自适应中值滤波和自适应加权均值滤波的混合滤波方法。该方法先将图像分为若干区域,并对每个区域进行噪声检测以实现两类噪声的分离,然后再分别采用自适应中值滤波和自适应加权均值滤波将分离出的脉冲噪声和高斯噪声去除。对这种新方法进行了计算机模拟实验。结果表明:新方法较前人提及的三种混合滤波方法具有更优的滤波性能,在有效抑制混合噪声的同时能很好地保护图像中的细节,为消除图像中的混合噪声提供了一种有效的途径。     

Time-domain split-step method with variable step-sizes in vectorial pulse propagation by using digital filters

Finite impulse response (FIR) and infinite impulse response (IIR) digital filters are proposed to allow for time-domain simulation of optical pulse propagation by using the operator-splitting technique. These filters simulate polarization mode dispersion and chromatic dispersion effects with acceptable accuracy in time-domain. An analytical relation between the coefficients of these filters and the simulation step-size is established to accommodate the possibility of carrying out the time-domain split-step method with variable split-step length at virtually no computational burden. The superiority of the proposed method over the conventional frequency-domain technique is particularly demonstrated in wavelength-division multiplexing (WDM) applications.     

Synthesis of optical PMD compensating filter using FIR lattice structure

We investigate the potential of n-stage optical finite impulse response (FIR) lattice filter for compensating first order polarization mode dispersion (PMD). This compensation is based on minimizing the differential group delay (DGD) between the two principal state of polarization (PSP) within a given frequency range. The filter is realized by concatenating optical delay lines, directional couplers, and phase shifters in a lattice architecture. A numerical simulation is performed for an 8th and 12th order filters to demonstrate the impact of using higher order filters. The results show that DGD can be reduced significantly as we increase the order of the filter.     

Robust modeling of acoustic paths using a sparse adaptive algorithm

Acoustic impulse response functions are generally sparse in nature and traditionally these are modeled by adaptive finite impulse response (FIR) filters trained using a least mean square (LMS) algorithm. The conventional LMS algorithm is not effective in modeling sparse systems and sparse LMS algorithms have been recently developed to improve the modeling in such scenarios. However, the traditional sparse LMS algorithms are not robust to disturbances at the error sensor and may diverge in some scenarios. With an objective to overcome this limitation of conventional sparse adaptive algorithm, this paper presents a robust sparse adaptive algorithm. The new algorithm has been shown to effectively model sparse systems in a robust manner. In addition, the algorithm has been successfully applied in modeling the acoustic feedback path in a behind the ear digital hearing aid.     

混沌通信系统中非线性信道的自适应组合神经网络均衡

针对混沌通信系统的非线性信道干扰问题,基于混沌信号重构理论和函数型连接神经网络理论,提出了一种横向滤波器与函数型连接神经网络组合(combination of transversal filter and functional link neural network,CFFLNN)的自适应非线性信道均衡器,并给出基于低复杂度归一化最小均方(NLMS)的自适应算法,并对该均衡器的稳定性以及收敛条件进行了分析.该非线性自适应均衡器充分利用了横向滤波器的快速收敛,以及函数型连接神经网络通过增大输入空间提高非线性逼近能力的特点,进一步提高均衡器的收敛速度和降低稳态误差.仿真研究表明：所提出的非线性自适应均衡器能够有效地消除线性和非线性信道干扰,均衡器输出信号能反映出混沌信号的特性,具有良好的抗干扰性能;且该均衡器的结构简单,收敛稳定性较好,易于工程实现. 关键词： 非线性信道 自适应均衡器 混沌吸引子 神经网络     

Jones precoder for polarization mode dispersion compensation

A new electrical-domain precoder is proposed to mitigate polarization mode dispersion (PMD) in optical communications by modeling a PMD-dominant fiber optical channel using a single input multiple output (SIMO) channel. Employing a bank of finite impulse response filters and a polarization modulator, and using parameters derived from the Jones matrix representation of PMD, the proposed precoder efficiently adapts to the time-varying nature of PMD and simultaneously pre-equalizes both polarization modes at the transmitter. The transmitter-only structure avoids losing phase and polarization information due to the nonlinearity of the commonly used square law direct-detection receiver. Analysis is performed to evaluate the impact of channel mismatch due to feedback delay, channel estimation errors, and the impact of the finite length of the precoder filters. The analytical results are used to guide selection of the appropriate feedback rate for the adaptive system. Extensive simulation results confirm the efficiency of the proposed Jones precoder, and present it as an effective, low-cost replacement to the complicated, expensive optical-domain counter-parts.     

Fiber chromatic dispersion measurement based on wavelength-to-time mapping using a femtosecond pulse laser and an optical comb filter

A novel method for the measurement of chromatic dispersion of an optical fiber based on wavelength-to-time mapping using a femtosecond pulse laser (FSPL) and an optical comb filter is proposed and experimentally evaluated. In the proposed approach, the spectrum of an ultrashort optical pulse generated by an FSPL is sliced by an optical comb filter. The spectrum-sliced optical pulse is then coupled into the optical fiber under test. Thanks to the chromatic-dispersion-induced wavelength-to-time mapping in the optical fiber under test, a time-domain waveform similar to the sliced spectrum is generated at the output of the optical fiber, with different frequency components having different time delays. The time delay vs. frequency data are then recorded for the estimation of the chromatic dispersion by using least square fitting. Chromatic dispersions of two types of optical fibers with different lengths are tested. The measured dispersion values agree well with those measured by the conventional modulation phase shift (MPS) method.     

Novel large negative dispersion and tunable zero dispersion wavelength of photonic crystal fiber

The article describes a novel doped CS₂ core photonic crystal fiber with high negative chromatic dispersion. The proposed design is simulated through a full-vector finite element method and anisotropic perfectly matched layers. The numerical results show that we can achieve a negative dispersion coefficient of ?5600 ps/(nm km) almost at the wavelength of 1.55 μm by carefully adjusting the proposed PCF structure parameters. The proposed PCF may have great potential applications in dispersion compensating, optical parametric amplification, and optical fiber communication.     

Dispersion compensation using high-positive dispersive optical fibers

The common and traditional method for optical dispersion compensation is concatenating the transmitting optical fiber by a compensating optical fiber having a high-negative dispersion coefficient.In this Letter,we take the opposite direction and show how an optical fiber with a high-positive dispersion coefficient is used for dispersion compensation.Our optical dispersion compensating structure is the optical implementation of an iterative algorithm in signal processing.The proposed dispersion compensating system is constructed by cascading a number of compensating sub-systems,and its compensation capability is improved by increasing the number of embedded sub-systems.We also show that the compensation capability is a trade-off between the transmission length and bandwidth.We use the simulation results to validate the performance of the introduced dispersion compensating module.Photonic crystal fibers with high-positive dispersion coefficients can be used for constructing the proposed optical dispersion compensating module.     

Equalization-enhanced phase noise induced timing jitter

In electronic digital signal processing based optical communication systems, digital equalization for chromatic dispersion interacts with local oscillator phase noise to produce equalization-enhanced phase noise (EEPN). In addition to both phase and intensity noises, EEPN also induces timing jitter to the equalized signal. For a 100?Gbit/s quadrature-phase-shift keying signal with laser linewidth of 300?kHz, the timing jitter is up to 20% of the symbol interval for a transmission distance of 1500?km.     

用于混沌时间序列自适应预测的一种少参数二阶Volterra滤波器

研究了二阶Volterra滤波器的一种乘积耦合近似实现结构及其非线性NLMS自适应算法,并用这种少参数二阶Volterra滤波器(RPSOVF)研究了一些混沌信号的非线性自适应预测性能.仿真研究结果表明:所给出的非线性NLMS自适应算法能够保证这种RPSOVF的稳定性和收敛性,且RPSOVF用这种非线性NLMS自适应算法能够自适应预测一些混沌时间序列. 关键词： 混沌 非线性自适应预测 Volterra滤波器 非线性NLMS自适应算法