一种用于光线性采样的载波相位估计算法（英文）

提出了一种改进的相位盲搜索算法,该算法通过两次寻找二次最小欧拉距离得到载波相位噪声的估计值.为验证该算法,搭建了一套光线性采样仿真系统,对符号率为10 Gbaud/s的16QAM光调制信号的星座图进行了测量,采样源为脉宽为500 fs、周期为10 ns的光频梳.仿真结果表明,当两个激光器线宽和小于10MHz时,经过该算法对相位噪声进行补偿后,10G-Gb/s的16QAM信号的星座图能够清晰展示.     

基于线型卡尔曼滤波器的双偏振并行载波相位恢复算法

针对偏振复用16阶正交幅度调制(16QAM)传输系统(PDM-16QAM),基于线型卡尔曼滤波器,提出了一种计算复杂度更低、线宽容忍度更高的双偏振并行载波相位恢复算法,使用两个偏振态内环和外环的符号信息对两个偏振态同时进行相位噪声估计。仿真结果表明,在传输速率为224Gb/s传输速率下,本文算法相比于单偏振卡尔曼滤波器算法的线宽容忍度提高了7倍,由原来的400kHz提高至2800kHz。此外,相比于单偏振卡尔曼滤波器载波相位恢复算法,本文算法并行处理符号个数提升了4倍左右,有效提高了算法的实时性,但是复杂度有所降低。最后,在传输速率为224Gb/s的PDM-16QAM传输实验中对本文算法进行了验证。     

基于投影直方图的CO-OFDM系统盲相位噪声补偿算法

提出了一种改进的盲相位噪声补偿算法——两阶投影直方图(two-stage PH)算法。利用一系列均匀分布的测试相位对接收信号进行相位旋转,将得到的信号向实轴投影,获取投影直方图;统计投影中心附近星座点的数量,以数量最多对应的测试相位作为粗相移值;以粗相移值为中心均匀取一定数量的测试相位,重复一阶投影直方图的估计步骤,得到精确的相移值进行相位补偿。通过基于光梳状谱的双向相干光正交频分复用无源光网络(COOFDM-PON)实验系统对该算法的性能进行了验证。结果表明:该方法对10×8Gbit/s的CO-OFDM系统的公共相位噪声有很好的补偿效果,将16正交振幅调制(16QAM)CO-OFDM系统的误码率降低至少2个数量级。该算法测试相位的个数仅需一阶投影直方图算法测试相位个数的1/4,极大地降低了系统的复杂度,可用于CO-OFDM系统的公共相位噪声补偿。     

基于K-means的自适应概率整形信号相位恢复算法

为解决未知概率整形因子信号的自适应相位恢复问题，提出了一种基于K-means聚类的自适应相位恢复算法。通过理论分析与数值仿真，验证了基于K-means聚类进行星座点模值半径重定位的可行性，将K-means聚类与前馈式载波相位恢复算法相结合，解决了概率整形信号经归一化处理后存在的星座点相对放大的问题，实现了未知概率整形因子信号相位的自适应恢复。对该算法在不同光信噪比、不同激光器线宽下的16正交幅度调制(QAM)与64QAM信号进行了分析，结果表明所提算法不仅可用于未知概率整形因子下信号的相位恢复，还可用于均匀QAM信号的相位恢复。所提算法在星座点模值的重新定位中考虑了噪声的影响，在相同的测试相位数量下可以实现更高精度的相位补偿，对于均匀QAM信号的光信噪比容忍度提升了约1 dB。     

CO-OFDM系统基于时频域卡尔曼滤波的相位噪声补偿算法

本文基于高阶正交幅度调制(QAM)和大线宽的相干光正交频分复用(CO-OFDM)系统,提出了一种基于时域和频域卡尔曼滤波联合估计的相位噪声补偿算法。该算法在发射端时域插入训练符号和导频序列,首先在接收端基于训练符号进行频域卡尔曼滤波得到信道估计。其次进行时域扩展卡尔曼滤波得到相位噪声粗略估计值。因此时相位估计值为复数值,为获得较好的补偿效果,根据导频序列数目,将每个OFDM符号分割为若干个亚符号。同时在导频序列处进行时域扩展卡尔曼滤波,通过在每个亚符号最后一个导频处进行线性插值得到每个采样点的相位噪声粗略估值。将粗略相位噪声补偿后的频域数据进行预判决后,最后进行时域相位噪声精细补偿。基于50Gb/sCO-OFDM系统传输100km进行了仿真验证,该算法较其他方法相比取得了较好的补偿效果。在激光器线宽为1MHz且16QAM以及线宽为800KHz且32QAM两种情况下,误码率性能可达前向纠错(FEC)上限。该算法能极大促进CO-OFDM系统在长距离接入网和城域网中的应用。     

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。     

基于量子粒子群优化的正交小波加权多模盲均衡算法

针对常数模盲均衡算法(CMA)均衡高阶正交振幅调制信号(QAM)存在收敛速度慢、稳态误差大的缺点, 提出了基于量子粒子群优化的正交小波加权多模盲均衡算法(QPSO-WTWMMA). 该算法根据高阶QAM信号星座图分布特点, 将量子粒子群优化算法(QPSO) 和正交小波变换融入于加权多模盲均衡算法(WMMA)中. 因而, 利用QPSO对均衡器权向量进行了优化, 利用正交小波变换降低了输入信号的自相关性, 利用WMMA选择了合适的误差模型匹配QAM星座图. 理论分析及水声信道仿真结果表明, QPSO-WTWMMA算法可以获得更快的收敛速度和更低的稳态误差, 在水声通信中具有重要的参考价值.     

基于扩展卡尔曼的PDM-16QAM偏振态和载波相位快速跟踪

在偏振复用(PDM)高速光通信系统的相干检测中,需要实现信号偏振态和载波相位的快速跟踪。将扩展卡尔曼滤波器用在偏振复用16进制正交振幅调制(PDM-16QAM)光调制信号相干接收机中,成功实现了偏振态和载波相位的快速精确跟踪。在单信道112Gb/s PDM-16QAM传输系统中,数值仿真发现,扩展卡尔曼滤波器所能跟踪的最大偏振态旋转速率可达级联多模算法的100倍,而且具有很好的收敛精度,其收敛速度和精度可以通过调优参量控制。使用扩展卡尔曼滤波器跟踪100kHz线宽18 Mrad/s偏振态旋转信号时,10-3误码率(BER)对应的接收机灵敏度代价仅为0.2dB。研究了应用于长距离传输光通信系统的扩展卡尔曼相干接收的性能。     

偏振分集相干光OFDM通信系统中的相位噪声消除

提出了一种基于偏振分集的相干光正交频分复用(OFDM)链路。然而相干检测对相位噪声比较敏感,偏振分集接收过程又会产生额外的乘性相位噪声,因此基于偏振分集相干光OFDM系统,提出了基于数字信号处理的相位噪声消除方案。在100km单模光纤中,以8Gbit/s的传输速率零误码传输16进制正交振幅调制OFDM信号,经相干检测之后,基于数字信号处理,对相干光OFDM信号完成了相位噪声消除,并对相位噪声消除后的信号星座图进行了实验结果分析。另外,还将经过相位噪声消除后的偏振分集相干光OFDM链路与其他相干光OFDM链路方案进行了性能对比,从而验证了此方案的优越性。     

一种光正交频分复用系统的联合相位均衡方法

正交频分复用（OFDM）技术加相干接收与数字信号处理法(DSP)的组合是超长距离光通信的理想模型。光OFDM系统对相位噪声十分敏感,必须对相位噪声进行补偿。提出一种基于正交小波基变换的光OFDM系统的联合相位均衡方案。该方案将块状导频周期性地插入OFDM信号,在接收端利用导频信息首先消除各个子载波的公共相位误差,然后采用自适应均衡方式消除每个子载波自身相位误差。仿真结果表明,对于二进制正交振幅键控(4QAM)调制信号,在采用常规的G.652光纤、100 Gb/s的相干光OFDM系统中,该联合相位补偿方法可使信号在满足传输系统的误码性能要求下,传输距离达到1000 km。     

Demonstration of high extinction ratio modal interference in a two-mode fiber and its applications for all-fiber comb filter and high-temperature sensor

We show that high extinction ratio (>20 dB) modal interference in a two-mode dispersion compensating fiber can be utilized to build a compact, easy-to-fabricate tunable all-fiber optical comb filter. Wavelength tunability over the full free spectral range of the comb filter is demonstrated with an electrical power of 115mW using an on-fiber thin film micro-heater deposited directly on the fiber. In another configuration, the comb filter is used as a temperature sensor with dynamic range of >300 °C and sensitivity of <0.1 °C. The temperature sensor is capable of measuring a temperature as high as 500 °C.     

Optical arithmetic unit using bit-WDM

A novel arithmetic unit is proposed consisting of a pipelined optical ripple carry adder that adds two words with bits multiplexed by different wavelengths on a single fiber. The addition result is returned to a fiber bus in the same format as the incoming words. The corresponding operand bit pairs are split off the fiber using wavelength division demultiplexers. Full adders compute the sum for each bit pair and the carry from the next lower significant bit pair. The full adder uses couplers and NOT, NOR and novel XOR logic gates constructed using semiconductor optical amplifiers for gain and wavelength shifting.     

Controllable optical bistability and multistability in a rare-earth-ion-doped optical fiber

We investigated the optical bistability and multistability in an Er³⁺-doped ZrF₄–BaF₂–LaF₃–AlF₃–NaF optical fiber inside an optical ring cavity. It is found that the optical bistability and multistability can be easily controlled via adjusting properly the parameters of the corresponding system. Our scheme may provide some new possibilities for technological applications in optoelectronics and optical-fiber communication.     

A high nonlinearity elliptical fiber for applications in Raman and Brillouin sensors

Raman and Brillouin effects have found special applications in distributed sensing for smart materials and structures. In these sensors, the fiber acts as a distributed sensor, sensing strain and temperature over a range of tens of kilometers and, at the same time, carries this information to the installation that will process them. In order to optimize the fiber to operate under the Brillouin and Raman regimes, a special elliptical fiber with small effective area has been designed, which will allow these sensors to cover longer distances and/or employ lower power lasers.     

Experimental measurement and analysis of the optical trapping force acting on a yeast cell with a lensed optical fiber probe

Based on an optical trapping system with a single-lensed fiber probe inserted at an angle, the sub-picoNewton trapping force acting on a yeast cell as a function of the displacement is measured experimentally by the static and dynamic methods, respectively, whose measurement processes are presented in detail. The measured maximum trapping efficiency is 0.07 in our experiment, which is an order of magnitude lower than that of the optical tweezers. The characteristics of the trapping force in the various horizontal directions are discussed. Finally, the analysis of the measurement error shows the factors and their magnitude which cause error, and offers a way to reduce the error in future.     

Dichroic property of the H2O-groups in α-quartz, LiNbO3 and LiTaO3 in the infrared range

The absorptive peaks of the H₂O-groups were observed in the infrared absorption spectra in the vicinity of 3480 cm⁻¹ in LiNbO₃ and LiTaO₃, and 3580 cm⁻¹ in α-quartz. The absorptions of these lines were found to depend on the vibration direction of the polarized incident light, showing the dichroic property in these crystals. The absorption of the ordinary ray waves is much larger than that for the E-ray waves in the crystals. This observation indicates that the direction of the bond vibrations for the H₂O-groups is perpendicular to the optic axis of crystals. The dichroic property of the H₂O-groups may serve as the tracer to study the local electric field in piezoelectric crystals.     

Temperature dependence of low loss polymeric AWG

We investigate on the variation of loss and temperature dependence of a polymeric arrayed waveguide grating (AWG) depending on its substrate, by fabricating 16-channel polymeric AWGs with various substrate conditions. Insertion loss for a polymeric AWG on a silicon substrate is measured as low as 3.1 dB. The temperature-dependent wavelength shift for a polymeric AWG detached from the substrate is maintained within 0.1 nm from 20 to 80 °C. But we observe a degradation of insertion loss and a little instability in wavelength characteristics both for the detached polymeric AWG and for a polymeric AWG on a polymer substrate. We investigate on those optical properties of the polymeric AWGs based on measured thermal expansion properties of the polymers.     

Method of state code matrixes in the realization of optical switching using Perfect Shuffle

Based on the Left Perfect Shuffle (LPS) optical communication network constructed by cascade multi-stage LPS interconnection, using Looping algorithm, any arbitrary sequence of the input signals can be realized. However, instead of obtaining the simultaneous state codes of the same level node switches through mathematical analytical expressions directly, only routing tags of each channel can be obtained through mathematical analytical expressions so as to draw out topological chart of the network to obtain the state codes implied in the chart. Thus, the states of the switches cannot be directly programmed and controlled by computer in practical application. In this paper, based on the Looping algorithm, a method of stage code matrixes is presented to resolve this problem. By using the method, the simultaneous state codes of the same level’s four node switches can be directly obtained, which is convenient for the computer to provide controlled signals needed to finish the permutation for each node switch. The method of stage code matrixes provides further theoretical basis for the realization of optical switching by integration of Perfect Shuffle and high-speed optical switches.     

All optical latches using quantum-dot semiconductor optical amplifier

The design and performance of two optical latches, the Set-Reset (SR) latch and D-Flip-Flop has been studied. These latches are the building blocks of large optical processors. The latches are built using two optical logic operations NAND and NOT. Both NAND and NOT operations are realized by using Mach-Zhender interferometer (MZI) utilizing semiconductor optical amplifier with quantum dot active region (QD-SOA). Nonlinear dynamics including carrier heating and spectral hole-burning in the QD-SOA are taken into account together with the rate equations in order to realize the all-optical logic operations. Results show that this scheme can realize the functions of Set-Reset latch and D-Flip-Flop at high speeds (∼250 Gb/s). The dependence of the output quality (Q factor) on QD-SOA parameters is also discussed.     

Dispersion-Managed Solitons in Multiple-Core Nonlinear Fiber Arrays

The variational principle is employed to obtain the evolution of the parameters of Gaussian and super-Gaussian chirped solitons that propagates through multiple-core nonlinear optical fiber arrays. This is governed by the dispersion-managed nonlinear Schrodinger's equation with strong dispersion management in the presence of linear coupling between the adjacent cores. The results are valid for any configuration of the cores.