相干光通信系统中的偏振控制

在相干光通信系统中,接收端的输入信号与本振信号的偏振状态(SOP)必须匹配,以保证其接收灵敏度。但是,通常使用的单模光纤,由于受温度或其它环境条件的影响,光纤中传输光的偏振态是不稳的,因此,有必要对传输的光信号进行偏振控制。本文所用的控制SOP的器件是挤压控制器,是一种线性双折射元件。     

光纤通信系统中偏振损耗对偏振态的影响

推导出具有偏振相关损耗(PDL)器件的Stokes模型,研究了光纤通信系统中PDL对光信号偏振态(SOP)的影响。数值模拟结果表明,入射信号光偏振度(DOP)小于1时,PDL对出射信号光的DOP和强度有直接影响;当入射光DOP等于1时,PDL对出射信号光的DOP没有影响,但随PDL的增加,出射光强度迅速减小,且信号光的SOP变化加剧。     

光偏振复用正交频分复用系统中基于联合近似特征矩阵对角化-独立分量分析的盲均衡算法

该文提出一种在光偏振复用正交频分复用(PDM-OOFDM)系统中基于联合近似特征矩阵对角化-独立分量分析(JADE-ICA)的盲解偏振复用算法。在传统的偏振复用系统中,恒模算法(CMA)被用于解偏振复用信号。然而,该方法需要多次对CMA滤波器系数更新,CMA收敛时间较长,并且CMA算法解偏振复用可能导致奇异性问题。该文结合对经典ICA算法及其模型的分析,提出将JADE-ICA算法用于PMD-OOFDM系统中进行解偏振复用信号。利用该方法,可以分离在发送端和接收端混有高斯白噪声的偏振信号成分,并且提高了系统中偏振信号的分离性能;同时,避免了传统CMA在解偏振复用中的奇异性问题。仿真结果表明,该文方法可以有效分离PMD-OOFDM系统中的偏振信号。     

基于MIMO构架的光OFDM系统研究

文章在分析无线正交频分复用(OFDM)技术和单模光纤偏振特性的基础上,研究了一种基于多输入多输出(MIMO)框架的光OFDM系统并搭建了实验平台.系统将两路12 Gb/sOFDM信号通过偏振复用为24 Gb/s信号,实现了两路信号的解调输出.实验证明,该系统可扩展光纤信道中的频谱划分,增大信道容量,具有较强的对抗光纤色散的能力.     

半导体光放大器中入射光偏振不平行近简并四波混频效应的理论研究

建立了当两输入光偏振方向不平行时半导体光放大器(SOA)中近简并四波混频(FWM)效应的宽带理论模型;以基于SOA的近简并FWM型波长转换器为例,通过数值模拟,对两输入光偏振方向不平行时,输入信号光、输入抽运光、两输入光之间的波长失谐量和偏振夹角对近简并FWM效应及波长转换特性的影响进行了理论研究。结果表明,对于输入信号光和抽运光来说存在着最佳功率值;增大输入信号光波长失谐量,转换效率随之下降;随着两输入光偏振夹角的增大,转换特性变差,同时输出光的偏振角随两输入光偏振夹角的增大而增大。     

光学测距与测速的方法和装置

该发明提供一种用于测量远目标的距离和速度的装置.该装置采用低能量光辐射源发射内部和外部相同的、波长被扫描的辐射信号.产生波长扫描的方法是改变光辐射源的输入电压.外部测距系统采用包括偏振装置在内的共用光学装置,向远目标发射外部信号,并接收从目标反射回来的一部分信号.第一光频外差装置提供用于外部反射信号与从外部光辐射信号得到的本机振荡信号的混频,从而产生输出信号,并由提供的装置测定该输出信号的频率代表值.内部处理系统将内部信号射入已知长度的光学延迟装置,由第二光频外差装置接收延迟的内部信号,并将这个信号与从内部光辐射信号得到的本机振荡信号混频,由提供的装置测定第二光频外差装置的输出信号的频率代表值.另外一些装置提供用于测定内、外光辐射信号的中心频率.最后,处理器利用从外部测距系统和内部处理系统得到的频率代表值和中心频率值计算出目标的距离和速度.     

基于偏振态变化时延估计的分布式光纤传感系统

提出一种基于偏振态（SOP）变化时延差估计的分布式光纤传感系统。本系统采用两个直流光信号在传感光纤中双向注入,振动会对正向和逆向光造成SOP变化,在各自的尾端利用起偏器检测SOP变化并转换为光强信息。两路信号间的时延差表明了振动的位置信息。对时延差形成的原因进行了理论分析,并阐明利用互相关算法计算该时延差并进行分布式传...     

用递归量子神经网络实现通信信号的识别与恢复

本文提出用递归量子神经网络(RQNN)在连续变量相干光通信系统中识别信号过滤未知噪声,其优点是不需要对信号和噪声有先验知识。为验证RQNN的作用,本文构建了偏振编码的连续变量相干光通信系统,接收端信号通过RQNN滤波后,相比未经降噪的信号误码率明显降低,增大了信道容量,表明了该方案是行之有效的。     

垂直双抽运结构PM-OFDM信号对全光波长变换系统的影响

对垂直双抽运结构的偏振复用信号在半导体光放大器(SOA)中的全光波长变换(AOWC)进行了研究。理论分析了激光器线宽对此系统性能的影响,仿真研究了偏振复用-正交频分复用(PM-OFDM)信号在此系统中传输的性能。仿真结果显示,当系统的光信噪比为10dB时,10Gbit/s的PM-OFDM信号经过SOA中的四波混频效应后,在接收端能够实现无串扰偏振不敏感PM信号的接收,其中x和y方向对应的系统误码率分别为1.16×10-4和1.06×10-5。仿真结果表明激光器线宽,OFDM信号的子载波个数,信道功率,以及OFDM调制格式均与系统波长转换效率有关,且仿真结果与理论推导结果一致。     

圆偏振光偏振复用激光通讯系统

提出了一种采用圆偏振光的偏振复用通讯系统。其基本设想是信号光在空间中以左 旋和右旋圆偏振光的形式进行传播,在接收端将这两种偏振光区分并分别接收。本文详细论证了在两个相对运动点之间采用圆偏振光实现偏振复用激光通讯的可行性。     

Nondeterministic endless control system for active polarizationcontrol

An active polarization-state control system is described for use in coherent fiber-optic communication systems. The active control system uses four piezostack fiber squeezers to enable control of the state of polarization (SOP) of the light over an unlimited range. The response time of the system is small enough to enable accurate tracking of changes in the SOP at a rate of up to 25 revolutions per second in the Poincare sphere representation. Unlimited control is achieved with a nondeterministic control algorithm. This makes the system insensitive to irregularities and unbounded instabilities of the control devices (e.g. drift). Experiments show that the SOP is accurately controlled by the system; the penalty loss due to residual mismatch in SOP is kept well below 1 dB even under dynamic circumstances     

An adaptive first-order polarization-mode dispersion compensationsystem aided by polarization scrambling: theory and demonstration

An adaptive polarization-mode dispersion (PMD) compensation system has been developed to cancel the effects of first-order PMD by producing a complementary PMD vector in the receiver. Control parameters for the PMD compensation system comprised of a polarization controller and a PMD emulator are derived from the nonreturn-to-zero (NRZ) signal in the channel to be compensated. Estimates of the link's differential group delay (DGD) and principal states of polarization (PSPs) based on this signal are reliable when the signal power is equally split between the link's two PSP's; however this condition cannot be assumed. To meet this requirement, we scramble the state of polarization (SOP) of the input signal at a rate much greater than the response time of the PMD monitor signal so that each sample represents many different SOP alignments. This approach allows the effective cancellation of the first-order PMD effects within an optical fiber channel     

Analysis of secrecy outage performance for full duplex NOMA relay systems with appearance of multiple eavesdroppers

Full-duplex (FD) relay systems including a transmit antenna selection and a non-orthogonal multiple access (NOMA) methods are analyzed under presence of multiple eavesdroppers. A channel state information of both the considered system and eavesdroppers is assumed to be outdated and eavesdroppers eavesdrop information signals independently. A closed-form of secure outage probability (SOP), secrecy throughput of every user is derived to evaluate the secrecy performance, and the mathematical analysis approach is verified by the Monte-Carlo simulation. Furthermore, the Golden-Section Search algorithm is proposed to find the maximum of the secrecy throughput of the considered FD-NOMA system. Numerical results indicate that there exists the SOP floor in the considered system and it is constrained by the channel gain of near user. Moreover, there is the optimal signal to interference plus noise ratio value which minimizes the SOP of the system regardless of the number of eavesdroppers. In comparison with half-duplex NOMA model, the SOP of FD-NOMA model is better.

     

New polarisation-control scheme for optical heterodyne receiver using two Faraday rotators

A new state-of-polarisation (SOP) control scheme using two Faraday rotators is proposed. It features low optical insertion loss and quick response. Experiment shows that the receiver output is stable regardless of drastic SOP changes in the signal.     

干涉型光纤传感器阵列消PIF技术的研究

针对低双折射光纤双光束干涉型传感器两臂偏振态随机变化引起的信号衰落,提出了一种新型消偏振方式,它可以在可见度略有下降的情况下,较好地消除偏振态变化引起的信号可见度的随机变化。该方案是通过相互正交的两个偏振态来补偿由于其中一个偏振态变化导致的干涉信号衰落。通过自动增益控制电路可以使传感信号稳定,能够在信噪比有所下降的情况下消除偏振衰落的影响,实现了干涉型光纤传感器的消偏振衰落。     

Effect of polarization mode dispersion on a coherent optical systemwith pilot carrier

The effect of fiber polarization mode dispersion (PMD) on a coherent optical system with pilot carrier is twofold. First, the PMD causes state of polarization (SOP) mismatch between the message signal and the pilot carrier. Second, the degrees of polarization (DOPs) of the message signal and pilot carrier are degraded by PMD. Because coherent reception relies both on the SOPs and DOPs of the waves, system performance is degraded by PMD. The effect of SOP mismatch causes intermediate frequency (IF) signal amplitude degradation, whereas DOP variation not only results in IF signal amplitude degradation but further induces IF noises. Analytical expressions are derived to evaluate the performance degradation. It is shown that there is no performance degradation if only one principle state of polarization is excited and maximum degradation occurs when both principle states of polarization are equally excited. It is found that significant degradation may happen when large differential group delay exists     

Secrecy Performance of CCRN with an EHAF Relay under Source and Destination Jamming

In this paper, we investigate the secrecy performance of a cooperative cognitive radio network (CCRN) considering a single energy harvesting (EH) half‐duplex amplify and forward (AF) relay and an eavesdropper (EAV). Power is allocated to each node under cognitive constraints. Because of the absence of a direct wireless link, secondary source (SS) communicates with secondary destination (SD) in two time slots. The SD and the SS broadcast jamming signal to confuse the EAV in the first and in the second time slots, respectively. The relay harvests energy in the first time slot and amplifies and forwards the signal to SD in the second time slot. The EAV employs maximal ratio combining scheme to extract the information. We evaluate the performance in terms of secrecy outage probability (SOP) of the proposed CCRN. The approximate expression of SOP is obtained in integration form. Improvement in SOP is expected for the proposed CCRN because of the use of jamming signals. The secrecy performance of CCRN improves with increase in primary transmit power, peak transmit power of secondary nodes, channel mean power, and energy conversion efficiency but degrades with increase in threshold outage rate of primary receiver and threshold secrecy rate. A MATLAB‐based simulation framework has been developed to validate the analytical work.     

Experimental demonstration of an all-fiber endless polarization controller based on Faraday rotation

An all-fiber device for the control of the state of polarization (SOP) is presented. The controller is high speed (its time response is less than 50 ms in the worst case), low loss (insertion losses are 2.5 dB independently of the input SOP), and low cost (is constructed with standard single-mode fiber). The polarization controller has been implemented using two Faraday rotators and works at 1550 nm. We have also designed an algorithm that confers an endless performance to the device. The controller has been included in a 2.5 Gb/s CPFSK optical coherent system and results are presented here.     

Chip-to-chip optoelectronics SOP on organic boards or packages

In this paper, we demonstrate compatibility of hybrid, large-scale integration of both active and passive devices and components onto standard printed wiring boards in order to address mixed signal system-on-package (SOP)-based systems and applications. Fabrication, integration and characterization of high density passive components are presented, which includes the first time fabrication on FR-4 boards of a polymer buffer layer with nano scale local smoothness, blazed polymer surface relief gratings recorded by incoherent illumination, arrays of polymer micro lenses, and embedded bare die commercial p-i-n photodetectors. These embedded optical components are the essential building blocks toward a highly integrated SOP technology. The effort in this research demonstrates the potential for merging high-performance optical functions with traditional digital and radio frequency (RF) electronics onto large area and low-cost manufacturing methodologies for multifunction applications.     

Polarization dependent gain in erbium-doped fiber amplifiers:computer model and approximate formulas

A computer model for polarization dependent gain (PDG) in Er-doped fiber amplifiers (EDFA) is presented. The model assumes that each erbium ion possesses an ellipsoidal gain surface and that all ion orientations are equally likely. By dividing the ions into subsets based upon orientation and computing the inversion of each subset in the presence of polarized pump and signal waves, the model predicts the dependence of the PDG induced by this polarization hole-burning (PHB) on the design of the EDFA, the signal degree and state of polarization (SOP), and the pump SOP. For moderate gain amplifiers (made from the same fiber) with the same gain peak wavelength and the same compression level, the magnitude of the PDG is nearly independent of the EDFA gain. Internal and random fiber birefringence are included to model real fibers. In fibers which cause the signal SOP to walk rapidly around the Poincare sphere, the PDG is reduced by a factor of 2/3 when compared with a linear polarization-maintained signal. Scrambled signals and partially-polarized saturating tones are also considered. Simple rules are derived for predicting the PDG of a given EDFA