光纤无线电系统中两路毫米波信号的同时产生

随着信息技术对通信系统的容量、带宽、安全性以及灵活性的要求越来越高,当今通信网络逐渐不能满足这种需求,光载毫米波系统已经成为目前国内外的研究热点。通过理论建模,在光载毫米波信号系统的发送端利用两平行的马赫-曾德尔调制器分别对两射频信号进行调制,经过长距离的光纤传输之后,在接收端利用两个光电探测器分别进行探测,通过仿真在接收端同时产生了两束高质量的毫米波信号,并得到了解调之后的基带信号的眼图。     

Generation and transmission of dispersion tolerant 10-Gbps RZ-OOK signal for radio over fiber link

We proposed and demonstrated the generation and transmission of 10-Gbps return-to-zero ON/OFF keying (RZ-OOK) signal using a new technique without pulse carving at transmitter.The new technique is char...     

光载毫米波在光纤中传输色散性能研究

提出了并理论分析了一种采用单电极Mach–Zehnder调制器(SD-MZM)产生光载毫米波的方案。采用电混频器将射频信号与基带数字信号混频后再利用单电极调制器产生双边带调制信号并发送至光纤,在基站使用一个交叉复用器(IL)将双边带信号的中心载波与一阶边带信号进行分离,中心载波可用于上行链路的光载波,而一阶边带产生光载毫米波;理论分析了该毫米波的色散特性并在仿真平台上验证了其正确性,研究发现由于光纤色散引起两个一阶边带的延时不同, 从而导致毫米波能量的损失和解调信号的码间干扰,限制了毫米波的最大传输距离。     

光码分多址多比特传输系统性能分析

:多比特传输是光码分多址通信的一种方案。本文对光码分多址多比特传输系统的误码性能进行了理论分析和计算机数字仿真。在系统中存在光电检测器散粒噪声、暗电流噪声、背景光、热噪声的情况下 ,分别对无光硬件限幅器和引入一个光硬件限幅器的多比特传输系统进行讨论 ,得出相应的误比特率表达式 ,该表达式明确、具体。分析结果表明 ,当接收功率较大时 ,多比特传输系统的误码性能优于相应的单比特传输系统。     

光载射频信号在多模塑料光纤中的传输特性研究

实验研究了光载射频信号在多模塑料光纤(POF)中的传输特性,将24GHz的正弦波信号与1.5Gbt/s的数字信号进行混频后再通过光强度调制器产生双边带调制光信号,将双边带调制信号通过多模POF发送至接收机,在接收机转化为24GHz的射频信号。实验结果表明,这种双边带调制的光载波射频信号可以在多模POF中传输50m后而功率代价可以忽略不计。     

基准信号的低相噪声长距离光纤传输设计

介绍了基准光传输设备的基本组成和原理,指出低相噪长距离光纤传输中的问题所在,并提供了解决问题的方法,即数模混合器件的选择及改进滤波器设计.     

基于三角波与HNLF的90GHz光生毫米波技术研究

通信技术的飞速发展对带宽提出了更高的需求, 移动通信向毫米波等更高频段发展 ,w波段(74 GHz)的宽频谱可以满足对高 流量的需求,为人们对w波段系统的研究提供了 巨大的推动力。本文理论提出并仿真了一种使用三角波信号作为射频信号驱动双驱动马赫增 德尔调制器(DDMZM)产生高阶边带,用高非线性光纤(HNLF)产生四波混频效应(FWM)进 一步提高倍频数的生成90 GHz毫米波的30倍频 光生毫米波产生方案。仿真结果表明,该实验 方案可以使用3GHz的射频信号生成90 GHz的光生毫米波信号,且搭 载2.5 Gbit/s的NRZ信号传 输20 km后,眼图清晰信号质量良好。另外分析了HNLF长度以及输入H NLF的光信号强度对FWM 的影响,得到能使HNLF产生最佳±15阶边带的条件,进而进一步优化 整个系统。     

环境温度对单模光纤中光信号传输延时的影响

分析了单模光纤中光信号传输延时随环境温度变化的原因,通过实验方法研究了单模光纤中光信号传输延时和环境温度变化的数值关系,给出了温度漂移系数的取值区间.     

射频信号光纤传输技术研究现状及进展

随着现代战场中电磁环境的日趋复杂化,情报侦察、电子对抗、通信和遥感等系统中不同频率、制式的射频(RF)信号密集交叠,RF信号光纤传输技术所具有的宽带、抗干扰和信号损耗小等优势将在这些系统中发挥关键性的作用。概述了RF信号光纤传输技术的特点和优势,介绍了国内外的研究现状及进展情况,展望了RF信号光纤传输技术的发展前景。     

相位偏移和分束比对八倍频光毫米波产生及传输的影响分析

相位偏移和分束比极大地影响了产生光毫米波信号的边带抑制比以及光纤无线(ROF)系统的BER。针对串联两个马赫-曾德尔调制器产生八倍频光毫米波信号的方案,利用贝塞耳级数展开的方法,推导了相位偏移和分束比影响下,光毫米波信号的严格通用解析解,当分束比偏离0.001,相位偏移1°时,边带抑制比可达35.9 dB,能够忽略谐波分量的影响。仿真结果表明,在BER=10-10的条件下,当八倍频光毫米波信号背靠背传输时,分束比偏离0.001和相位偏移1°的功率代价仅为0.001dB,经20 km标准单模光纤传输后的功率代价为0.145 dB,系统性能良好。     

Design of low‐power all‐optical networks under the constraint of four‐wave mixing

In this paper, we propose a static lightpath establishment method to design low‐power all‐optical networks under the constraint of four‐wave mixing (FWM). Since the FWM causes nonlinear interchannel crosstalk, it degrades the communication quality of optical signals. The FWM crosstalk effect becomes strong in a fiber as the number of passing optical signals increases. Therefore, we should reduce the number of optical signals passing through the same fiber from the perspective of the FWM. Meanwhile, in order to enhance the power efficiency of optical amplifiers, which are deployed at each optical fiber, it is preferred that multiple optical signals are transmitted in the same fiber. In order to decrease the power consumption while keeping high communication quality, the proposed method statically selects routes, wavelengths, and fibers for each traffic demand, considering the FWM crosstalk effect and the usage efficiency of the optical amplifiers. We show the performance of the proposed method through numerical experiments.     

音频信号数字化光纤传输实验仪信道的设计与实现

介绍音频信号数字通信实验装置设计的实现过程,该装置以FPGA为主控芯片,以光纤为通讯媒介,将音频信号数字化后通过光纤实现传输,并对电路各个模块的功能及实现加以说明。实验装置采用分模块式的设计,设计思路灵活,结构清晰。电路在Altium Designer和Protel99中设计完成,并且在QuartusⅡ环境下用VerilogHDL语言进行编程并对程序进行仿真。该装置已做成了实体,可以实现音频信号的发射与接收,达到设计提出的要求。     

子载波OFDM毫米波接入信号的光学产生与应用研究

研究了一种下行链路采用64 阶正交幅度调制-正交频分复用(QAM-OFDM)信号和上行链路采用8阶相移键控(PSK)-OFDM 信号的全双工光载无线通信(RoF)系统。其中,下行链路承载的是60GHz不同子载波数量(64,256)的 光生64QAM-OFDM毫米波接入信号。数值模拟仿真证明:光生 64QAM-OFDM毫米波接入信号 的峰均比(PAPR)随着子载波数量的增加而增大;当下行链 路接收功率为－18dBm时,相比较其它3种子载波数量而言, 子载波数为256QAM-OFDM毫米波接入信号 的接收灵敏度最好,误码率(B ER)近似为10－3.7;当上行链路的接收功率高于 －28.5dBm时,接收信号的BER在 10－3以下。     

双向混合信号光纤传输系统的设计与实现

介绍了一种新的多路信号光纤数字化传输方法,基于FPGA设计了混合信号光纤传输系统,并通过实验验证了系统的准确性.该系统不仅能传输模拟信号还能传输数字信号,不仅能传输低速数字信号还能传输高速脉冲信号,此外还能实现双向CAN通信.     

Performance of fiber delay‐line buffers in asynchronous packet‐based optical switching networks with wavelength conversion

A major challenge in asynchronous packet‐based optical networks is packet contention, which occurs when two or more packets head to the same output at the same time. To resolve contention in the optical domain, two primary approaches are wavelength conversion and fiber delay line (FDL) buffering. In wavelength conversion, a contending packet can be converted from one wavelength to another in order to avoid conflict. In FDL buffering, contending packets can be delayed for a fixed amount of time. While the performance of wavelength conversion and FDL buffering has been evaluated extensively in synchronous networks with fixed‐sized packets, in this paper, we study the performance of FDL buffers in asynchronous packet‐based optical networks with wavelength conversion. An analytical model is proposed to evaluate the performance in terms of packet loss probability and average delay. Extensive simulation and analytical results show that, with appropriate settings, FDL buffers can perform much better in switches with wavelength conversion than in switches with no conversion. Copyright © 2014 John Wiley & Sons, Ltd.     

SPM/XPM/FWM对高速光传输的影响与对策探讨

文章探讨了SPM、XPM、FWM等与折射率相关的光纤非线性效应对高速长距离光传输的影响及减轻其影响程度的技术措施。     

Electrospinning Preparation and Drug‐Delivery Properties of an Up‐conversion Luminescent Porous NaYF4:Yb3+, Er3+@Silica Fiber Nanocomposite

Up‐conversion (UC) luminescent porous silica fibers decorated with NaYF₄:Yb³⁺, Er³⁺ nanocrystals (NCs) (denoted as NaYF₄:Yb³⁺, Er³⁺@silica fiber) are prepared by the electrospinning process using cationic surfactant P123 as a template. Monodisperse and hydrophobic oleic acid capped β‐NaYF₄: Yb³⁺, Er³⁺ NCs are prepared by thermal decomposition methodology. Then, these NCs are transferred into aqueous solution by employing cetyltrimethylammonium bromide (CTAB) as secondary surfactant. The water‐dispersible β‐NaYF₄:Yb³⁺, Er³⁺ NCs are dispersed into precursor electrospinning solution containing P123 and tetraethyl orthosilicate (TEOS), followed by preparation of precursor fibers via electrospinning. Finally, porous α‐NaYF₄:Yb³⁺, Er³⁺@silica fiber nanocomposites are obtained after annealing the precursor fibers containing β‐NaYF₄:Yb³⁺, Er³⁺ at 550 °C. The as‐prepared α‐NaYF₄:Yb³⁺, Er³⁺@silica fiber possesses porous structure and UC luminescence properties simultaneously. Furthermore, the obtained nanocomposites can be used as a drug delivery host carrier and drug storage/release properties are investigated, using ibuprofen (IBU) as a model drug. The results indicate that the IBU–loaded α‐NaYF₄:Yb³⁺, Er³⁺@silica fiber nanocomposites show UC emission of Er³⁺ under 980 nm NIR laser excitation and a controlled release property for IBU. Meanwhile, the UC emission intensity of IBU–α‐NaYF₄:Yb³⁺, Er³⁺@silica fiber system varies with the released amount of IBU.     

Performance limitation of laser satellite communication due to vibrations and atmospheric turbulence: down‐link scenario

In this paper, we analyse the effects of vibrations and the atmosphere on the performance of a broadband laser inter‐satellite link (BLISL) which was studied within the framework of the BLISL joint Israeli–German applied research project. The use of optical radiation as a carrier between satellites and in satellite‐to‐ground links enables transmission using very narrow beam divergence angles. Due to the narrow beam divergence angle and the large distance between the satellite and the ground station or airplane the pointing is a complicated process. Further complication results from vibration of the pointing system caused by two fundamental mechanisms of a stochastic nature: (1) tracking noise created by the electro‐optic tracker and (2) vibrations caused by internal satellite mechanical mechanisms. Additionally an inhomogeneity in the temperature and pressure of the atmosphere leads to variations of the refractive index along the transmission path. These variations of refractive index as well as pointing vibrations can cause fluctuations in the intensity and the phase of the received signal leading to an increase in link error probability. In this paper, we develop a bit error probability (BEP) model that takes into account both pointing vibrations and turbulence‐induced log amplitude fluctuations (i.e. signal intensity fading) in a regime in which the receiver aperture D₀ is smaller than the turbulence coherence diameter d₀. Our results indicate that BLISL can achieve a BEP of 10^?9 and data rate of 1Gbps with normalized pointing vibration of G_T*σ_θ²=0.05 and turbulence of σ_X=0.3. Copyright © 2003 John Wiley & Sons, Ltd.     

Surface Chemistry Routes to Modulate the Photoluminescence of Graphene Quantum Dots: From Fluorescence Mechanism to Up‐Conversion Bioimaging Applications

The bandgap in graphene‐based materials can be tuned from 0 eV to that of benzene by changing size and/or surface chemistry, making it a rising carbon‐based fluorescent material. Here, the surface chemistry of small size graphene (graphene quantum dots, GQDs) is tuned programmably through modification or reduction and green luminescent GQDs are changed to blue luminescent GQDs. Several tools are employed to characterize the composition and morphology of resultants. More importantly, using this system, the luminescence mechanism (the competition between both the defect state emission and intrinsic state emission) is explored in detail. Experiments demonstrate that the chemical structure changes during modification or reduction suppresses non‐radiative recombination of localized electron‐hole pairs and/or enhances the integrity of surface π electron network. Therefore the intrinsic state emission plays a leading role, as opposed to defect state emission in GQDs. The results of time‐resolved measurements are consistent with the suggested PL mechanism. Up‐conversion PL of GQDs is successfully applied in near‐IR excitation for bioimaging.     

On the performance of joint space‐frequency pre‐filtering and equalization for downlink multi‐carrier code division multiple access

We analyze the performance of joint space‐frequency pre‐filtering and equalization techniques for downlink multi‐carrier code division multiple access in terms of average bit error rate performance. Several linear power allocation strategies combined with single‐user equalization schemes are compared with a joint pre‐filtering with an equal power constraint at the base station and maximal ratio combining at the mobile terminals. Our bit error rate analysis obtained in this paper facilitates predicting the performance of various space‐frequency pre‐filtering schemes without massive simulations. Copyright © 2011 John Wiley & Sons, Ltd.