大气闪烁对无线光CDMA通信系统性能的影响

将光CDMA技术应用到无线光通信中。提出了基于脉冲位置调制的二维大气无线光CDMA通信系统，并分析了该通信系统的性能。考虑多用户干扰、APD噪声以及热噪声等干扰因素的影响，采用数值分析的方法，详细分析了大气湍流引起的大气闪烁对二维无线光CDMA通信系统误码率的影响。结果表明，大气闪烁是影响二维无线光CDMA系统误码率性能的一个重要因素；当大气闪烁的对数方差较小(如σ2s=0.1)时，该系统可以实现高速率通信；当大气闪烁的对数方差较大(σ2s≥0.2)时，在有限的光功率条件下，该系统难以实现通信，需要采用信道编码技术来提高系统的误码率性能。     

Capacity of wander and spread beams in log-normal distribution non-Kolmogorov turbulence optical links

We model the average channel capacity of optical wireless communication systems in weak turbulence horizontal channels, using the log-normal distribution models. The effects of beam wander and spread, pointing errors, turbulence inner scale, turbulence outer scale and the spectral index of non-Kolmogorov turbulence on system's performance are included. The model can evaluate the influence of the atmospheric turbulence conditions in the performance of a ground-to-train optical wireless communication system.     

光通信技术在物联网中的应用

介绍了物联网的定义及结构;从感知层和网络层角度,探讨了光通信技术(光纤通信和无线通信)在物联网中的应用现状和前景.光纤通信、近距离无线通信、移动通信是物联网开发的基础,制定物联网各个层面上统一的、标准化协议和技术标准是物联网未来发展必须解决的关键和难点.     

水下无线光通信自组织网性能分析

针对无线光通信工作频率高、通信频带宽、数据传输能力强、传输距离远的特点,提出建立水下无线光通信自组织网。为解决水下无线光通信点对多点通信的问题,提出了一种组合折反射镜,为建立移动自组织网（MobileAdhocNetwork,MANET）提供条件。研究利用OPNET对按需距离向量协议（AODV）进行仿真,通过设置移动节点参数模拟水下无线光通信自组织网,分析了不同网络规模、不同节点速度、不同发包率对网络的吞吐量、时延、误比特率等性能的影响。仿真结果表明,AODV在节点速度5m／s--10m／s以下,网络规模10个节点左右,发包率小于20packets／s时对网络拓扑变化的适应性较好。     

西安理工大学无线光通信系统自适应光学技术研究进展

总结了国内外自适应光学技术在无线光通信系统应用中的研究进展和技术分类,同时介绍了西安理工大学在该领域的工作,包括有波前测量的自适应光学系统、无波前测量的自适应光学系统、液晶空间光调制器波前校正、偏摆镜和变形镜组合的波前校正、空间光光纤耦合自适应光学波前校正等。自适应光学技术可有效修正无线光通信系统中由大气湍流引起的畸变波前,提高耦合效率和通信性能。虽然这些方法在理论分析和工程实际中尚不完善,但不失为人们在该领域进行的有益探索。     

移动式无线激光通信基台结构与装调研究

针对近年各国对无线激光通信的应用越来越多,设计一款快速组网的无线激光通信基台。主要介绍了移动式无线激光通信基台的结构设计和5条光轴平行度的装调方法,满足系统通信的需要,同时对通信接收系统中直角棱镜的固定和调整机构做了介绍,并对5条光轴的平行度进行了简单的误差分析,可以满足系统的10平行度的要求。     

Resources scheduling for data relay satellite with microwave and optical hybrid links based on improved niche genetic algorithm

The formation of the Space-based Information System with the technology of high performance optical inter-satellite communication and the realization of global seamless coverage and mobile terminal accessing are the necessary trend of the development of optical and microwave hybrid communication. Considering the resources, missions and restraints of data relay satellite optical and microwave hybrid links system, a model of hybrid links resources scheduling is established and a scheduling algorithm based on an improved niche genetic algorithm is put forwarded. According to the multi-user-satellite, multi-time-window, multi-class-antenna and a number of missions with priority weight, the scheduling schemes are generated randomly to begin with and evaluated with the fitness functions. To obtain an optimal scheduling result, an improved niche genetic algorithm is adopted to optimize the scheduling schemes. The simulation result reveals that a satisfactory result is obtained and the improved niche genetic algorithm has advantages in both efficiency and performance in a scenario including a relay satellite with 2 optical antennas and 1 microwave antenna for user satellites connection, 8 user satellites with 64 missions. The simulation indicates that the model and the optimization algorithm are suitable for multi-user, multi-mission and multi-class-antenna hybrid communication recourses scheduling problem.     

Capacity for non-Kolmogorov turbulent optical links with beam wander and pointing errors

The performance of optical wireless communication links depends strongly on the atmospheric conditions and the parameters of the link such as the propagation distance, the operation wavelength, jitter variance, attenuation coefficient and effective beam spot radius at the receiver. The analytical expression for the evaluation of the average capacity of optical wireless communication systems is derived, using the gamma-gamma distribution in the non-Kolmogorov atmosphere turbulence. The impact of atmospheric attenuation, beam wander and pointing errors on the average of the optical wireless communication link is investigated. It is shown that the capacity has a fluctuation curve, when power law α increases, and the power law α of minimum point in fluctuation curve is bigger as the non-Kolmogorov turbulence strength is stronger.     

Quantum-correlation-based free-space optical link with an active reflector

We present a quantum-correlation-based free-space optical(FSO) link over 250 m using an outdoor active reflector 125 m from the transceiver station. The performance of free-space optical communication can be significantly degraded by atmospheric turbulence effects, such as beam wander and signal fluctuations. We used a 660 nm tracking laser to reduce atmospheric effects, by analyzing the fast beam wander and slow temporal beam drift, using this information to correct the quantum channel alignment of the 810 nm signal photons. In this work, the active reflector consisted of a mirror, a 6-axis hexapod stage, and a long-range wireless bridge. The slow drift of the beam path due to outdoor temperature changes was steered and controlled using wireless optical feedback between the receiver units and the active reflector. Our work provides useful knowledge for improved control of beam paths in outdoor conditions, which can be developed to ensure high quality quantum information transfer in real-world scenarios, such as an unmanned FSO link for urban quantum communication or retro-reflective quantum communication links.     

Fundamental performance limit of covert free-space optical communications

With the development of wireless communication, free-space optical (FSO) communication is becoming a highly promising technology. In this paper, we consider the covert FSO communication between two legitimate peers in the presence of an external warden. We establish a system model under a nonnegativity constraint, a peak optical intensity constraint, an average optical intensity constraint and a covertness constraint. For the considered system, the optimal input signal is shown to follow a uniform distribution. Based on the optimal input signal and covertness constraint, we obtain an upper bound that should be satisfied by the transmitter’s peak optical intensity, which provides a basis for the transmitter to set the transmit optical intensity. We also derive the upper bound of maximum amount of information transmitted covertly, which reveals the fundamental performance limit of covert FSO communication. Finally, we verify the theoretical analysis by numerical simulations.     

Numerical evaluation of radiation and optical coupling occurring in optical coupler

We present in this work a new mathematical model to analyze and evaluate optical phenomena occurring in the nonuniform optical waveguide used in integrated optics as an optical coupler. By introducing some modifications to the intrinsic integral, we perfectly assess the radiation field present in the adjacent medium of the waveguide and, thus, follow the evolution of the optical coupling from the taper thin film to the substrate and cladding until there is a total energy transfer. The new model that is introduced can be used to evaluate electromagnetic field distribution in three mediums that constitute any nonuniform optical couplers presenting great or low wedge angles.     

Acrylic and metal based Y-branch plastic optical fiber splitter with optical NOA63 polymer waveguide taper region

We proposed a simple low-cost acrylic and metal-based Y-branch plastic optical fiber (POF) splitter which utilizes a low cost optical polymer glue NOA63 as the main waveguiding medium at the waveguide taper region. The device is composed of three sections: an input POF waveguide, a middle waveguide taper region and output POF waveguides. A desktop high speed CNC engraver is utilized to produce the mold inserts used for the optical devices. Short POF fibers are inserted into the engraved slots at the input and output ports. UV curable optical polymer glue NOA63 is injected into the waveguide taper region and cured. The assembling is completed when the top plate is positioned to enclose the device structure and connecting screws are secured. Both POF splitters have an average insertion loss of 7.8 dB, coupling ratio of 55: 45 and 57: 43 for the acrylic and metal-based splitters respectively. The devices have excess loss of 4.82 and 4.73 dB for the acrylic and metal-based splitters respectively.     

Indoor optical wireless systems–a review

This paper reviews the research effort to date into optical wireless communication systems, both in academic and industrial contexts. The idea of using the optical medium for wireless communications is not new, having been proposed as a means for indoor communications almost two decades ago. However, the last few years have seen an explosive interest in the potential for free space optical systems to provide portable data communications. One of the prime motivators for reconsidering the use of an optical carrier in the wireless context is the demand for greater transmission bandwidths. The radio frequency spectrum is already exceedingly congested and frequency allocations of sufficient bandwidths are extremely hard to obtain. Further, for the high bandwidth services envisaged, the use of microwave or mm-wave systems will be required, where device technology is currently either expensive or immature. Proponents of optical wireless systems argue that the optical medium is the only cost-effective way to provide high bit-rate mobile services to volume markets. This paper identifies the technical obstacles and limitations of indoor optical wireless delivery in addition to techniques for mitigating these effects and shows that infrared is a viable alternative to radio for certain applications. This revised version was published online in November 2006 with corrections to the Cover Date.     

Characteristics of radio transmission over polymer optical fiber for indoor wireless coverage

The characteristics of radio over polymer optical fiber (RoPOF) are evaluated for indoor or in-building wireless coverage. The frequency responses and the third order intermodulation distortion products of the RoPOF link are investigated. The eye diagrams and EVM values of signals carrying quadrature-phase-shift-keyed (QPSK) data and global system for mobile (GSM) signals are measured to evaluate the transmission performance. The interference measurements with FDM are also carried out. The results show that although the nonlinear distortion and power loss deteriorate the system to some extent, making use of passband transmission, RoPOF can provide fairly good transmission performance for wireless applications.     

Observation of V-type electromagnetically induced transparency and optical switch in cold Cs atoms by using nanofiber optical lattice

Optical nanofiber (ONF) is a special tool to achieve the interaction between light and matter with ultralow power. In this paper, we demonstrate V-type electromagnetically induced transparency (EIT) in cold atoms trapped by an ONF-based two-color optical lattice. At an optical depth of 7.35, 90% transmission can be achieved by only 7.7 pW coupling power. The EIT peak and linewidth are investigated as a function of the coupling optical power. By modulating the pW-level control beam of the ONF-EIT system in sequence, we further achieve efficient and high contrast control of the probe transmission, as well as its potential application in the field of quantum communication and quantum information science by using one-dimensional atomic chains.     

Design and analysis of the optical transceiver for mobile atmospheric laser communication

The concept of mobile atmospheric laser communication (MALC) is introduced in this paper. Atmospheric attenuation, turbulence-induced scintillation and beam wander cause deep fades in the beam power and degrade the optical channel. The optical transceiver presented in this paper is designed for a MALC test system. Currently achievable hardware performance capabilities for the MALC terminals are used as input parameters to the analysis. A novel optical transceiver structure is designed. Link margin is analyzed using the MALC analysis software, our optical link analysis program. Data rate, bit-error rate, prime transmit     

Analysis of inter-satellite free-space optical link performance considering different system parameters

The welcome and adaptation of optical wireless technology by the modern era has brought forward the concept of an inter-satellite free-space optical communication system. In the present work, I study the combined effect of selection of different operating wavelengths and detector types along with the pointing errors at the transmitter and receiver side on the performance of an inter-satellite free-space optical link. The link performance has been optimized by measuring and analyzing the bit error rate and quality-factor of received signal under different scenarios. Performance of the inter-satellite link has also been investigated considering different modulation formats and data rates for LEO and MEO distances.     

GHz frequency band soliton generation using integrated ring resonator for WiMAX optical communication

New system of optical soliton signal generation with a high frequency band is presented. Microring resonator can be used to generate soliton signals with high frequency of GHz. These signals can be transmitted via a wireless network system known as WiMAX, which is providing broadband wireless access up to 50 km. The soliton pulses are more stable with less loss during propagation which is good candidate compare to other current optical waves used in optical communication. In this study, soliton pulses with full width at half maximum of 3 MHz and FSR of 85 MHz could be generated using an add/drop filter system which is used to generate high frequency signals, required for wireless network systems. These pulses can be used as carrier signals in order to transmit information codes without significant changes, thus improving transmission quality and delivery of the right information.     

纤维光锥有效透过率的理论分析

光锥的有效透过率不仅影响光锥与CCD的耦合效率,而且会影响到耦合器件的信噪比.本文主要从理论上讨论了影响光锥有效透过率性能的因素,从纤维光学元件的实际内部结构推导出了其实际有效填充率,从光线在光锥中的传输特征推导出了光线在光锥中传播时产生的衰减损耗,最后提出了提高光锥有效透过率的方法和途径.     

光锥与CCD耦合效率的理论分析

光锥与CCD的耦合技术是研制ICCD图像传感器的关键技术,本文主要从理论上分析并讨论了光锥与CCD耦合器件的耦合效率及其影响因素,进一步分析讨论了耦合效率对耦合器件信噪比的影响.证明了光锥与CCD的耦合效率不仅降低ICCD探测效率而且降低ICCD信噪比,并提出了提高光锥与CCD耦合效率的方法和途径.