基于广义回归神经网络的CO-OFDM系统非线性均衡

针对高阶正交幅度调制和大线宽相干光正交频分复用(CO-OFDM)系统,提出了一种基于广义回归神经网络(GRNN)的非线性均衡算法。将接收端进行相位噪声恢复之后的批量数据作为训练数据样本,通过训练学习得到GRNN的唯一参数平滑因子,然后对测试数据进行非线性均衡。对传输速率为50Gb/s,传输距离为100km的CO-OFDM系统进行了仿真验证。仿真结果表明,在大线宽和高阶调制下,GRNN非线性均衡算法对系统非线性损伤的补偿效果优于相应反向传播神经网络(BPNN)非线性均衡算法,且其训练运行时间远小于BPNN。GRNN非线性均衡算法能极大促进CO-OFDM系统在中长距离光纤传输中的应用。     

相干光正交频分复用系统中射频导频和扩展卡尔曼滤波联合的相位噪声补偿算法

针对大线宽和高阶圆形正交幅度调制(C-QAM)的相干光正交频分复用(CO-OFDM)系统,提出一种基于射频导频(RF-Pilot)和时域扩展卡尔曼滤波相结合的相位噪声补偿算法。该算法通过在接收端预设的RF-Pilot进行时域相位噪声粗补偿,并进行信道估计和均衡。再对信道均衡后的频域数据进行预判决,结合判决后的时域数据和信道均衡后的时域数据,进行扩展卡尔曼滤波,实现相位噪声的最终补偿。基于传输速率为50Gb·s~(-1)和传输距离为100km的CO-OFDM系统在C-16QAM和C-32QAM两种调制格式下进行了算法的仿真验证。仿真结果表明,该算法相较于原RF-Pilot算法,具有较好的相位噪声补偿效果,且频谱利用率并未显著降低,算法复杂度并未显著增加。激光器线宽为2.1MHz,且使用C-32QAM时,该相位噪声算法补偿的误码性能可达到前向纠错上限,从理论上证明使用该算法可提高CO-OFDM系统对激光器线宽的容忍度,线宽较宽的廉价分布式反馈激光器可作为CO-OFDM系统的发射端光源和接收端本地振荡。该算法能扩展大线宽CO-OFDM系统在长距离接入网和城域网中的应用。     

两种离子交换型变折射率微透镜

分别求得制作自聚焦平面微透镜的开孔式和掩盘式离子交换的相应扩散方程的解,导出掩盘式微透镜的最佳折射率分布,给出微透镜的成像矩阵,制得掩盘式平面微透镜阵列并给出其成像照片及基本参数.     

A theoretical method based on Fourier spectrum analysis for the focusing performances of the X-ray compound refractive lenses

It is important to predict the intensity distribution in focusing plane for designing the X-ray compound refractive lenses. On the basis of analyzing the structure of X-ray compound lenses and comparing it with Praunhofer diffraction system, it is concluded that the X-ray focusing system can be regarded as a kind of Praunhofer diffraction system. Therefore, a method based on Fourier spectrum analysis is presented to predict the intensity distribution in the focusing plane for the X-ray lenses. A brief analysis on the relationship between the parameters of X-ray lenses and their focusing performance is also given in this paper.     

贝塞尔晶格中环状涡旋孤子的研究

贝塞尔晶格是在自聚焦光折变晶体中通过光诱导产生的,研究了涡旋光束在贝塞尔晶格中的传输特性。通过数值仿真发现改变参数的值,即改变晶格上外加电场强度的大小、贝塞尔晶格的横向尺度系数以及晶格深度,会出现完全不同的传输结果。这些结果表明:由于晶格的存在,输入的环状涡旋光束可以克服自身因聚焦非线性而引起的方位角调制不稳定性;当条件适当时,涡旋光束可以形成环状涡旋孤子并稳定地传输很长距离;当输入光束的能量并不是完全落在贝塞尔晶格的环状信道中时,在传输过程中光束可能演变成为一个大环环绕一个小环的双环结构。     

基于光子晶体单向传输波导的通道下路滤波器(英文)

基于光子晶体单向传输波导,设计了一种三端口和两种四端口结构的通道下路滤波器.为取得100%的通道下路效率,运用实时耦合模理论对这三种结构进行了分析.理论分析表明该通道下路滤波器比利用光子晶体普通介质波导设计的通道下路滤波器具有更简单的结构,降低了器件制作难度.用有限元方法对滤波器结构进行了数值仿真分析,仿真计算结果表明所设计的三种结构具有超过90%的通道下路效率,与理论分析结果相符合.     

Compact triplexer in two-dimensional hexagonal lattice photonic crystals

We design a compact triplexer based on two-dimensional (2D) hexagonal lattice photonic crystals (PCs).A folded directional coupler (FDC) is introduced in the triplexer beside the point-defect micro-cavities and line-defect waveguides.Because of the reflection feedback of the FDC,high channel drop efficiency can be realized and a compact size with the order of micrometers can be maintained.The proposed device is analyzed using the plane wave expansion method,and its transmission characteristics are calculated using the finite-difference time-domain method.The footprint of the triplexer is about 12× 9 μm,and its extinction ratios are less than –20 dB for 1310 nm,approximately –20 dB for 1490 nm,and under –40 dB for 1550 nm,making it a potentially essential device in future fiber-to-the-home networks.     

Novel iteration-free blind phase noise estimation for coherent optical OFDM

We propose a novel iteration-free blind phase noise estimation scheme for coherent optical orthogonal frequency division multiplexing （CO-OFDM） systems. In the new algorithm, the cost function is selected as the similar expression with real and imaginary parts as that in the modified constant modulus algorithm, and the new cost function is derived under some assumptions, where it is infinitely approximated by the sine and cosine functions. By means of the analytical formula of the cost function, the initial coarse common phase error can be obtained with only some samples, where the algorithm avoids computational complexity of conventional blind phase noise compensation scheme. In CO-OFDM systems with high-order modulation format （32 quadrature amplitude modulation） and narrow linewidth lasers, it is proved by the simulation results that the nhase noise can be effectively compensated with the proposed blind estimation method.     

大数值孔径自聚焦平面微透镜列阵研究

采用离子交换工艺,在PS—1玻璃基片上制作自聚焦平面微透镜列阵,由于窗口区凸起,数值孔径高达0.58。本文还对窗口凸起的透镜特性和窗口直径对折射率分布的影响进行了理论分析,得到了有益结果。最后对样品的光学特性进行了讨论。