Development of LC Optics for Free-space Laser Communications

Free-space laser communications is a very flexible means to connect end users to a high-bandwidth data network via ground-based terminals on top of buildings or to bring a variety of data services to remote locations via satellite terminals in space. External influences on the optical link due to atmospheric turbulence and vibrations in the transmitter's environment require some method of beam control to stabilize the optical link and maintain a high transmission rate. Liquid crystal (LC) optics can provide a compact and low-power solution to beam control in laser communications systems. Besides reviewing recent Japanese activities in the field of free-space laser communications, this paper summarizes four years of research in designing and experimentally evaluating LC beamdeflectors and adaptive lenses that feature simple driving circuitry and have been manufactured specifically with regard to laser communications.     

卫星相干激光通信系统与技术发展

自由空间光通信(Free Space Optical Communication,FSOC)尤其是基于相干体制的卫星激光通信,正逐渐成为突破微波通信瓶颈、建设天地一体化网络、实现高速数据传输的重要手段.总结了欧空局、德国、日本及国内卫星相干激光通信的重要进展,给出了成功验证的相干激光通信系统的激光器、传输速率、多普勒频...     

Transparent Optical Intersatellite Link Using Double-Sideband Modulation and Homodyne Reception

A coherent, transparent optical communication system has been developed for free-space lasercomm terminals. The laser synchronisation scheme has been chosen such that the transmission of either an ensemble of subcarrier-modulated signals or of a binary baseband signal is equally possible. By using double-sideband modulation and an average-power-limited booster amplifier, the link capacity for subcarrier-multiplexed transmission approaches that of a homodyne PSK transmission system to within 0.5 dB.     

The SILEX optical interorbit link experiment

The European Space Agency (ESA) has instigated an in-orbit demonstration project known as SILEX (semiconductor laser intersatellite link experiment) using a pre-operational link between the French SPOT-4 low earth orbit satellite and the ESA Advanced Relay and Technology Mission Satellite (ARTEMIS). Such an optical communication system brings some new and challenging requirements. In particular, the communication beam, which has a divergence of around 6 μrad, must achieve and maintain a very demanding pointing accuracy in the presence of both host satellite vibration and relative satellite motion. The authors provide an overview of the SILEX project and describe a novel pointing mechanism     

Optimal Equalization of Distortions due to Group Delay Ripples of Chirped Fiber Bragg Gratings (CFBG)

We present a closed solution for an optimal equalizer which compensates for signal distortions caused by group delay ripples in chirped fiber Bragg gratings (CFBG) employed for dispersion compensation in optical communication systems. The theory is verified with the help of group delay measurement results of a dispersion compensating CFBG and the improvements achieved by the equalizer are presented on the basis of simulation results.     

Optically Preamplified Direct Detection in the Presence of Modulator Chirp

We analyze the impact of modulation induced chirp on optically preamplified direct-detection communication systems transmitting over dispersion-free channels, as found in optical free-space communication links. We show that commonly used quantitative measures of chirp (the small-signal chirp parameter and the effective chirp parameter) can fail to describe changing chirp characteristics under large-signal modulation in a satisfactory manner. We present an extended chirp model that lends itself both to measurement and simulation in a straightforward way. Regardingreceiver performance, we show thatreturn-to-zero (RZ) coded data signals can experience receiver sensitivity degradations of several dB due to spectral broadening of the chirped signal. By optimizing optical and electrical receiver bandwidths the penalty can be kept considerably lower than for receivers optimized for chirp-free signals. For non return-to-zero (NRZ) coding, chirpcan even improve receiver sensitivity by means of a pulse compression effect in the presence of narrow-band optical filters, leading to reduced inter-symbol interference (ISI). In our simulations and for the measurements, we exploit the variable chirp characteristics of a dual-drive electro-optic Mach-Zehnder modulator.     

星间激光通信终端性能对比分析

提出了两种星间激光通信终端性能的比较方法，可为空间激光通信系统设计提供参考。以SILEX研究计划为例，简要分析了各种轨道之间光通信系统的特性及未来光学终端的升级方案。     

Multifunctional Optical Terminals for Microsatellite Clusters – Design Tradeoffs

We study optical terminals with both communication and ranging capabilities for their potential use in short range free-space applications, typically encountered within a cluster of microsatellites. For our considerations we assume satellites with a unit mass between 10 kg and 100 kg, with mutual distances on the order of a few km, and per link data rates range from a few kbits/s to some 100 Mbit/s. We discuss possible network topologies and multiple access methods, andcompare the performance characteristics of different intensity modulation formats, taking into account not only the task of communication but also that of accurate intra-cluster distance measurement. Our considerations revealbasic tradeoffs to be observed when designing such multifunctional optical terminals.     

Space Laser Communications: A Review of Major Programs in the United States

This paper reviews space laser communication technology developments in the United States of America from 1960 to 2000. Early programs initiated and funded by government agencies closely followed the advancements made in laser transmitter technology. In the 1980s, growing commercial interest in long distance terrestrial fiber cables contributed significantly to the advancement of critical components. While several laser communications terminals were fully developed and flight qualified, actual space flight tests were not conducted due to funding problems, schedule overruns, and changed priorities. The first opportunity for commercial intersatellite links, the Iridium program, was missed due to a lack in technology readiness. The second opportunity for large-scale commercial deployment of very wide band terminals was the Teledesic program. The Teledesic terminal combined the most advanced design concepts with the latest component technologies. Unfortunately, business considerations forced the program to be cancelled in 1998.     

Alphasat Aldo Paraboni,an advanced Q/V band mission space segment

This paper provides an overview of the space segment of the Aldo Paraboni mission on the Alphasat satellite and the technology programme that has developed one of the most powerful geostationary satellites in Europe. The Aldo Paraboni technology demonstration payload, funded by ASI under European Space Agency's Advanced Research in Telecommunications System Programme, was embarked as a hosted payload on the Alphasat satellite, launched on 25 July 2013. The Aldo Paraboni payload is composed of two main elements, an experimental communication payload operating at Q/V bands (COMEX) and a scientific payload formed by 2 beacons at Ka and Q bands (SCIEX). The Aldo Paraboni payload is a key technology element of the Aldo Paraboni Mission, which covers two main objectives: the communication segment of the mission aims at assessing the performance of satellite communication links at Q/V bands and investigating use Fade Mitigation Techniques (FMT, eg, Adaptive Coding and Modulation defined in DVB‐S2 standard), while the scientific segment aims at characterizing in time, space, and frequency the K and Q band radio channel over Europe to permit development and improvement of propagation channels for slant paths.     

Key payload technologies for future satellite personal communications: A European perspective

This paper deals with satellite payload architectures adequate for the provision of universal mobile telecommunication services (UMTS) by medium altitude earth and geostationary orbit (MEO and GEO) satellites. The payload concept introduced is based on a transparent transponder with onboard digital signal processing (DSP) operations and digital beamforming at the traffic carrier level (narrowband beamforming). The emphasis of the paper is on key design aspects and technology considerations of the payload processor unit (PPU), which includes multiplexing/demultiplexing and digital beamforming operations, and on the antenna and RF signal handling subsystems. For completeness, a review on the European digital technology is also presented. The development of such a payload architecture is in line with present and planned activities of the European Space Agency (ESA) for MEO and GEO orbit systems, which are also implicitly discussed in the paper.     

空间激光通信发展现状及组网新方法

针对现有无线电方法空间信息传输能力不足问题,简要分析了空间激光通信的优势,重点介绍了国内外空间激光通信的发展现状与计划,研究了空间激光通信的未来发展趋势。针对卫星小型化、网络化的发展趋势,提出了一种基于逆向调制技术的空间激光通信及组网方法。结合我国空间激光通信发展现状与不足,总结并分析了相关领域的关键技术。     

激光星间链路发展综述：现状、趋势、展望

由于激光通信在空间传输中波长短且方向性强,已成为下一代卫星通信与导航的重要手段。激光星间链路的高速率、高带宽、高安全性等特点,可以提供高质量卫星空间通信,同时其还可以提高星间测距的精度,因此,构建激光星间链路成为下一代卫星网络的研究重点之一。文中首先从技术层面介绍激光星间链路的基本组成,主要介绍了卫星激光建链模式、卫星激光信号调制模式及卫星激光载波波长三个重要技术点。从技术到现象,根据不同轨道高度和不同的任务需求,按照发射时间顺序综合调研并总结了近年来国内外典型中高轨和低轨卫星激光通信成果的发展现状与未来计划。通过调研,进一步从宏观角度分析出卫星激光通信发展标准化、兼容化、网络化和商业化四个趋势,并从微观角度总结了卫星激光终端弹性化和模块化的发展方向。最后,除了作为通讯手段,展望了星间激光链路用于卫星激光测距的良好前景。通过对激光星间链路的现状、趋势和展望的综合分析,旨在为未来激光星间链路的设计与优化提供一定的借鉴和参考,并为我国未来星间激光通信和测距技术的发展及研究提供方向参考。     

全双工逆向调制回复空间光通信系统性能评价

基于逆向调制反射器(MRR)的空间光通信系统因其结构紧凑、可免去链路一端的捕跟(APT)系统、功耗低等优点,是空间光通信系统研究热点之一。提出采用双波长激光发射实现全双工逆向调制回复空间光通信结构,并基于该结构对强度调制解调模式,通信距离为300 km,通信速率为1 GHz下的地面站对近地小卫星全双工通信链路进行了链路计算及通信误码率的分析。当MRR端口径为0.1 m时,通信链路余量大于5 dB,通信误码率优于10-15,满足通信链路的要求。并进一步分析了仿真结果存在的缺陷。结果表明所提出的空间光通信结构在小卫星对地面站全双工激光通信是可行的,是未来空间光通信系统发展趋势之一。     

光学空间通信进展

回顾了光学空间通信的发展，介绍了美国、日本及欧空局光学空间通信的研究现状和光学空间通信系统，并对我国光学空间通信系统的发展提出了建议。     

一种大气激光通信系统抗干扰调制/解调技术

空间光通信以大气为介质进行信息传输时,不可避免地受到大气散射、大气湍流及背景光等因素的影响。针对大气信道对通信质量的影响,提出了基于激光偏振态参数的调制与解调技术,设计了一种基于偏振移位键控(PolSK)的大气激光通信系统并对其原理进行了简要分析。该通信系统采用偏振移位键控的调制方式,即利用圆偏振光的两种旋态(左旋和右旋)进行编码、调制从而实现数据的传输,接收端采用平衡探测方法进行光信号解调。对系统性能进行仿真分析,结果表明,基于激光偏振态参数的调制与解调技术在抗大气环境干扰、提高数据传输速率和降低误码率等方面具有优越性,在未来的空间激光通信领域有广阔的发展空间和应用前景。     

混沌空间光通信研究进展

随着空间通信技术的迅猛发展,人们对信息安全的需求愈发迫切。基于半导体激光器的空间激光通信凭借其终端体积小、功耗低、高带宽以及无电磁频谱约束等特点,已广泛应用于空间高速通信领域。激光混沌通信技术作为一种在物理层对空间光通信加密的安全技术手段,逐渐成为了空间光通信的研究热点。结合当前国内外自由空间光通信、混沌激光通信、混沌空间光通信的发展历程,介绍了近年来混沌空间光通信关键技术的研究进展,主要包括自由空间光通信快速跟瞄技术、混沌空间光通信大气湍流抑制技术和激光混沌空间同步技术。最后结合当前混沌空间光通信发展现状与不足,对混沌空间光通信的研究方向和可借鉴的关键技术进行了展望,旨在为该领域的进一步发展提供参考和借鉴。     

基于自由空间光通信技术的研究

自由空间光通信（FSO）是以大气为传输媒介,以激光的波长作为载体用以携带高速信息的无线传输技术,它是光通信与无线通信的结合,并兼有光纤通信的高速传输与无线通信可灵活移动等优点,无须挖沟,无须申请频率许可证,为当今卫星通信技术的首选。关键技术主要对FSO通信系统中接收灵敏度进行分析以及对接收的光学系统中跟踪原理进行剖析,为进一步提高自由空间光通信的性能作铺垫。     

带有前置EDFA卫星相干激光通信终端的信噪比分析

卫星激光通信链路是一项实现卫星大规模星座组网的关键技术。相干激光链路灵敏度高、抗背景干扰、速率升级空间大,在星间激光链路中应用广泛。文章建立了带有前置掺铒光纤放大器(EDFA)的卫星相干激光通信终端的信噪比分析模型,仿真分析了EDFA功率增益、EDFA噪声系数、本振光功率、信号光功率、光放后端光带宽、基带前端电带宽对终端输出信噪比的影响以及各种输出噪声功率占比的情况,得到了带有前置EDFA卫星相干激光通信终端的信噪比参数特性。     

Simplified Design Approach of Reliable Transparent Optical Networks

Transparent optical networks will play an important role in the near future. The aim of this work is to provide a simplified design approach how to utilize the new feature “optical transparency” in WDM based optical networks. Therefore optical nodes and transmission links are characterized and a set of simplified parameters and rules describing the transparent sub-networks is presented. In this way the complexity originating from physical constraints is reduced substantially, simplifying the management of these optical networks and the physical parameters which will be implemented in the routing protocols. This contribution is a compendium of results of the BMBF KomNet project in the field of optical networks optimisation.