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An opportunity arose to demonstrate optical crosslink pointing between two CubeSats in LEO using spacecraft not specifically designed for that purpose. The AeroCube-7 spacecraft, designed for optical downlinks as part of the Optical Communication and Sensor Demonstration mission, was tasked to point its communications laser at the ISARA spacecraft to demonstrate the capability of one CubeSat to track another in LEO. The ISARA spacecraft, which does not carry a data receiver, but does carry a short-wave infrared camera (SWIR) as part of the CUMULOS payload, was tasked to track the AeroCube-7 spacecraft and use the SWIR camera to record the OCSD laser. The SWIR images were downloaded over an RF channel and used to evaluate the pointing and tracking of both spacecraft. Two successful tests of crosslink pointing were completed between AeroCube-7 and ISARA, providing a demonstration in principle of the capability, and laying the groundwork for more refined experiments that will use this technique for on-orbit measurements of beam profiling. Further tests between AeroCube-11 and ISARA are also in preparation to demonstrate crosslink pointing in a more-challenging orbital configuration.

Laser technology has observed a great advancement over the last few decades. This technology is used for a wide range of applications including medical sciences, military, industrial manufacturing, electronics, holography, spectroscopy, astronomy and much more. Military operations often demand a secure and timely transmission of a massive amount of information from one place to another. Until now, the military has relied on the radio spectrum for effective communication, which is vulnerable to security threats and susceptible to electromagnetic interference (EMI). Also, this spectrum is hard-pressed to meet the current bandwidth requirement for high-resolution images, on-air video conferencing and real-time data transfer. Therefore, the focus has shifted to visible and infrared spectrum using laser technology which is capable of providing secure data transfer because of its immunity to EMI. The probability of intercepting a laser signal is very low due to its narrow beam divergence and coherent optical beam, making the laser a suitable candidate for secure military tactical operations. Besides the communication aspect, the highly directive nature of a laser beam is also used as a directed energy laser weapon. These highly powerful and light weighted directed energy laser weapons are very cost-effective countermeasures for airborne threats. Furthermore, laser sensors are deployed in the battlefield or in space for tracking the path of a wide range of military vehicles like missiles, unmanned aerial vehicles, fighter aircraft, warships, submarines, and so on. Advancements in space operations and laser technology have offered synergistic possibilities of using lasers from space-based platforms during military operations. In this paper, we are providing our readers with a comprehensive study of laser applications, used by the military, to carry out tactical operations on the ground or space-based platforms. Also, an intensive investigation on the development of laser technology for sensors, range-finders and target designators that are used for intelligence, surveillance and reconnaissance is presented in the paper. The advancement of laser communication for military purposes and its current state of the art is reviewed as well as some recent scientific developments in the area of high-energy directed laser weapons are discussed, which have revolutionized military battlefields. Therefore, this manuscript highlights recent trends and engineering breakthroughs for the use of lasers in tactical operations.

Bu çalışma kaynak düzleminde şişe ve sinus oyuk ışınları kullanan kablosuz optik haberleşme hatlarında parıldama davranışı ve hata olasılığı tahminini içermektedir. Haberleşme linki üzerindeki performasına ek olarak, şişe ışınının yayılma ve kurtosis parametresi de analiz edilmiştir. Şişe ışının parıldamasının analitik türetimi Rytov parıldama teorisinden faydalanarak yapılmıştır. Denklemler çözülmesi çok zor olduğundan yayılma özellikleri, kurtosis parametresi, parıldama tahmini ve hata olasılığı değerleri rastgele faz tabakaları yöntemi kullanılarak elde edilmiştir. Aynı merthodu kullanara sinus oyuk ışınının da parıldama ve bit hata oranı hesaplanmıştır. Sonuçlarımız gösteriyor ki, asimetrik şişe ışınlarının parıldaması aynı şartlarda karşılık gelen simetrik ışınlara nazaran daha azdır. Bu da bize asimetrik ışınların sabit sinyal gürültü oranında daha düşük bit hata oranına sahip olduğunu sonucunu getirmektedir. Zayıf türbülansta sinüs oyuk ışınının parıldaması Gaussian ışınından daha az olduğu için, bu ışın zayıf türbülansta bit hata oranı bakımından daha vantajlı görünmektedir. Parıldama sonuçları küresel dalga ile karşılaştırılmış ve elde edilen hata olasılığı değerleri analitik formül ile kaşılaştırılıp bu çalışmada çizilmiştir. This thesis involves scintillation behavior, and probability of error estimation of optical wireless communication links using bottle and sine hollow beams on the source plane. In addition to performance over communication link, propagation and kurtosis parameter of bottle beams are analyzed as well. Analytical derivation of scintillation of bottle beam is performed utilizing Rytov scintillation theory. Since equations becomes too complicated to solve intensity profiles, kurtosis parameter, scintillation estimation, and probability of error values of selected bottle beams are obtained benefiting from random phase screen approach. Utilizing the same method, scintillation index and bit error rate(BER) of sine hollow beam are evaluated too. Our results show that asymmetric bottle beams have less scintillation value under the same conditions as compared to corresponding symmetric ones. This brings us, asymmetric bottle beams have less bit error rate when signal to noise ratio is constant. Since, scintillation index of sine hollow beam becomes less than Gaussian beam in weak turbulence, this beam seems advantageous considering BER for weak turbulence. Scintillation results are compared with spherical wave and obtained probability of error values are compared with the analytical formula and plotted in this study. 93

Free-space optical (FSO) communications offer a resilient and flexible alternative communications medium to current radio technologies, which are increasingly threatened by our peer adversaries. FSO provides many advantages to radio technologies, including higher bandwidth capability and increased security through its low probability of detection (LPD) and low probability of interception (LPI) characteristics. However, current FSO systems are limited in range due to line-of-sight requirements and suffer loss from atmospheric attenuation. This thesis proposes the use of arrayed optical emitters for FSO communication by developing a link-layer protocol that leverages the inherent error correction of quick response (QR) encoding to increase bandwidth and overcome atmospheric loss. Through the testing of a system built with commercial-off-the-shelf equipment and a survey of current optical transmitter and receiver technology, this link-layer protocol was validated and estimated to provide similar data rates to current single emitter FSO systems. Various limitations were discovered in the current structure of the protocol. Future work should be conducted to correct inefficiencies in the QR encoding format when applied to a transmission medium. Additionally, technological advancements in hardware systems, including the large-scale production of VCSELs and faster high-speed cameras, must be achieved before such an FSO would be viable for large-scale use. http://archive.org/details/arraybasedfreesp1094559655 Captain, United States Marine Corps Approved for public release; distribution is unlimited.

We report the development of the multimode fiber-coupled superconducting nanowire transition edge sensor with high system detection efficiency at optical and near-infrared wavelength. The SNTES consists of an absorber, a sensitive thermometer, and a weak thermal link to a cold bath, For a SNTES optimized to detect single photons, the temperature change caused by the absorption of a single photo is read out by the thermometer, and the system resets by cooling through the thermal link. The graded index (GRIN) lenses were spliced to the end of the multi mode fiber with a 50 µm diameter core, and the incident light spot diameter was focused to approximately 20 µm at the active area, which is 28 µm diameter, allowing a good optical coupling. We have achieved a nominal coupling efficiency of 91 % and system efficiency of 76 % by the SNTES at 1310 nm -1350 nm. The developed practical SNTES presented in this paper could open a new frontier for a wide range of applications at optical and infrared wavelength.

Laser communication is of growing importance for space programs and is utilized in several recent satellite missions, since it offers the advantages of high data rates over long distances. Since 2007, the German Space Operations Center (GSOC) of the German Aerospace Center (DLR) is involved in a number of projects in which laser communication plays a significant role, such as TerraSAR-X, TDP-1, EDRS-A and the upcoming EDRS-C. The role performed by GSOC is different for each of these missions, thus it covers a broad portfolio of operational experience in laser communication. For TerraSAR-X, a low earth orbit (LEO) satellite, GSOC performs the satellite as well as all payload operations. TerraSAR-X is equipped with a Laser Communication Terminal (LCT) as secondary payload, which is capable of inter-satellite (ISL) as well as space-to-ground links (SGLs). The development of these LCTs is led by the Space Administration of DLR, funded by the Federal Ministry for Economic Affairs and Energy, and performed by TESAT Spacecom GmbH. In contrast, EDRS-A is a hosted payload on a geostationary (GEO) satellite and the first step in the European Data Relay System, which will soon be supported by a second relay terminal, EDRS-C. The relay system offers LEO satellites more possibilities for high speed data downlinks via laser. It is a commercially used service with quite demanding requirements concerning the availability of this downlink. For EDRS-A, GSOC fulfills the role of the LCT payload control center. For EDRS-C, the task of GSOC is extended to dedicated satellite operations including the LCT payload. To address the demanding requirements, all processes on GSOC side are completely automated. ESA´s TDP-1 (Technology Demonstration Payload No.1) project is the proof-of-concept for EDRS. It is a collaboration between DLR, ESA, and TESAT-Spacecom. The mission involves LCTs installed as secondary payloads on board a variety of LEO and GEO satellites as well as on ground, allowing for ISLs as well as for SGLs. Here, GSOC fulfills the role of the Mission Control Center, which includes collection of orbit and availability data, calculation of feasible link slots, scheduling of customer link requests, and generation of operational products for the LCT payloads of the involved spacecraft. One important aspect of this advanced concept is the connection to multiple control centers or associated facilities (like TECO, INMARSAT, ESOC), which is a necessary prerequisite for successful laser communication between different satellite projects. This paper gives an overview of the operational concepts of GSOC within the four mentioned projects, with a focus on our involvement in the TDP-1 program.

The paper first establishes the mathematical model of bit error rate of OOK system and an effective mathematical model of performance analysis based on exponentiated Weibull distribution channel model that can accurately describe the fluctuation probability distribution of light intensity on limited receiving aperture, simulates and verifies the correctness of both models, analyzes the effect of different aperture means on the improvement of atmospheric laser communication performance and provides an efficient mathematical tool for the budgeting of system power.

Kablosuz haberleşme sistemleri için en önemli sorun atmosferik türbülanstır. Temelde radyo frekans haberleşme sistemleri için geliştirilmiş birçok modülasyon ve kodlama tekniği son yıllarda atmosferik türbülansın sönümleme etkisini azaltmak adına kablosuz optik haberleşme sistemlerine uyarlanmaya başlanmıştır. Spektral verimliliği artıran uzaysal modülasyon ve sistem performansını geliştiren uzay-zaman blok kodlama teknikleri yakın zamanda radyo frekans sistemler için birleştirilerek kullanılmıştır.Bu tezde radyo frekans sistemler için geliştirilmiş uzay-zaman blok kodlamalı uzaysal modülasyon tekniği kablosuz optik haberleşmeye uyarlanmıştır. Önerilen tekniğe ait analitik bit-hata oranı ifadesi, log-normal, gamma-gamma dağılımlı ve görünür ışık kanallar için darbe genlik modülasyonu kullanılarak çıkarılmıştır. Analitik ifadenin doğruluğu simülasyonlarla desteklenmiş, sistem sadece uzaysal modülasyon tekniği kullanan bir sistemle bit hata oranı açısından karşılaştırılmış ve uzay-zaman blok kodlamalı uzaysal modülasyon tekniğinin bit-hata oranı açısından yalnızca uzaysal modülasyona olan üstünlüğü gösterilmiştir. The major drawback of the optical wireless communication systems is athmospheric turbulence. Various modulation and coding techniques of radio frequency systems are adapted to the optical communication systems for degrading effect of athmospheric turbulance. Spatial modulation and Space-time block coding schemes are two promising techniques for improving spectral efficiency and enhancing the system performance. Recently STBC and SM techniques are combined for RF systems.In this thesis we propose space-time block coded spatial modulation for optical wireless communication. We derived the analytical bit-error rate expression of the proposed system for log-normal, gamma-gamma athmospheric turbulence and visible light channels where the pulse amplitude modulation is considered. We confirm the accuracy of our analytical expression through computer simulations. Additionally, we compare our proposed optical STBC-SM scheme with the optical SM scheme in terms of BER performance. The results show that STBC-SM technique offers significant improvements compared to SM. 90

Free-space optical (FSO) communication is a very attractive technology offering very high throughput without spectral regulation constraints, yet allowing small antennas (telescopes) and tap-proof communication. However, the transmitted signal has to travel through the atmosphere where it gets influenced by atmospheric turbulence, causing scintillation of the received signal. In addition, climatic effects like fogs, clouds and rain also affect the signal significantly. Moreover, FSO being a line of sight communication requires precise pointing and tracking of the telescopes, which otherwise also causes fading. To achieve error-free transmission, various mitigation techniques like aperture averaging, adaptive optics, transmitter diversity, sophisticated coding and modulation schemes are being investigated and implemented. Evaluating the performance of such systems under controlled conditions is very difficult in field trials since the atmospheric situation constantly changes, and the target scenario (e.g. on aircraft or satellites) is not easily accessible for test purposes. Therefore, with the motivation to be able to test and verify a system under laboratory conditions, DLR has developed a fading testbed that can emulate most realistic channel conditions. The main principle of the fading testbed is to control the input current of a variable optical attenuator such that it attenuates the incoming signal according to the loaded power vector. The sampling frequency and mean power of the vector can be optionally changed according to requirements. This paper provides a brief introduction to software and hardware development of the fading testbed and measurement results showing its accuracy and application scenarios.

TDP-1 is a quasi-operational technology demonstration payload, designed to prove the concept of data transfer between low-orbit observation satellites and earth via a geostationary relay satellite in between the communication chain. This detour allows to significantly increase transferable data volume at reduced latency time, and is performed with the help of Laser Communication Terminals (LCTs) on board the low-orbit as well as the geostationary satellite, from which the data is immediately downlinked via Ka-Band. In this framework, TDP-1 is the successful precursor mission for the forthcoming European Data Relay Satellite System (EDRS). A dedicated operational concept has been developed by DLR GSOC as TDP1 Mission Control Center. The concept is based on heritage programs TerraSAR-X and NFIRE and includes all necessary tasks and steps like calculation of feasible link slots based on satellite orbit and availability data, scheduling of customer link requests, and generation of operational products for the involved spacecrafts to execute the links. This paper gives an overview of the current Mission Control Center System Design of the TDP-1 program and its operational experiences.

Optical feeders for geostationary High Throughput Satellites (HTS) systems based on 1.55μm wavelength technology are expected to enable to transmit up to several terabits over one active link. A desirable option of transmission architecture is an optical feeder link transparent with respect to the user air interface. This can be implemented using either a digital or an analog modulation of the optical carrier. The digital option increases the optical bandwidth to be transmitted, however it benefits from error correcting codes, interleaving and framing which are efficient against atmospheric turbulence impairments. The analog option is more efficient concerning the optical bandwidth; however the atmospheric turbulence impairments can only be mitigated by a more complex optical ground terminal. Both analog and digital options could be feasible in the 2025-2030 time-frames but the digital option is more mature with respect to the atmosphere impairments mitigation techniques.

U ovom radu opisan je alarmni sustav temeljen na laserskim zrakama. Dana je teorijska podloga potrebna za sintezu traženog sustava. Analizirani su sklopovski zahtjevi, izrađene su tiskane pločice, te je napisan programski kod testnog sustava. Prekidom zrake alarm se aktivira i šalje obavijest na mobitel putem SMS poruke In this paper the alarm system based on a laser beams is explained. Theory needed for synthesis of the required system is given. Hardware requirements are analysed, printed circuit boards are fabricated and software for the test system is written. When a laser beam is blocked an alarm is triggered and SMS message is sent to a mobile phone.

Free Space Optical (FSO) communications use modulated collimated light energy, usually in the form of an infrared (IR) laser, to transmit data. This affords FSO many appealing qualities such as a very high bandwidth capability, a high level of security through a low probability of detection (LPD) and a low probability of intercept (LPI), and a signal that is impervious to radio frequency (RF) interference or regulation. Military communications require broadband capabilities at the highest level of security in an incredibly dense RF operating environment. The bandwidth and security qualities of FSO make it an attractive technology for military communications. However, a strict line of sight (LOS) requirement and link attenuation in poor atmospheric conditions limit its application. Several companies are developing and implementing FSO communication solutions worldwide in response to a demand for broadband connectivity without RF interference at a relatively low price point. Recent advances in hybrid FSO-RF systems have improved performance in all atmospheric conditions. This research conducts a survey of the current state of FSO communications and analyzes its suitability as a military communication solution. The findings indicate further research, development, and link performance improvement is required before actual implementation of FSO communications can occur. http://archive.org/details/freespaceoptical1094543886 Captain, United StatesMarine Corps Approved for public release; distribution is unlimited.

Inmarsat’s geostationary satellite Alphasat, launched on July 25, 2013, is the largest European telecommunications satellite ever built with a weight of 6.6 tons. For technology demonstration it is carrying different payloads, hereunder the laser communication terminal (LCT) built by Tesat-Spacecom and operated by DLR/GSOC. Its purpose is to establish bidirectional data links with data rates of up to 1.8 Gbit/s. Links can be either within space, so called inter-satellite links (ISL) to counter terminals in low Earth orbit (LEO), or from the geostationary satellite to terminals mounted on ground stations on the Earth’s surface, space-toground links (SGL). This paper gives an overview about the LCT operations aboard Alphasat and its counter terminals. The corresponding work flow from visibility computations over link scheduling until command generation is described. Furthermore, it provides a deeper insight into the flight dynamics tasks that comes along with the operations of an LCT, such as visibility calculations and pointing performance analysis. The results of the first successfully performed links are presented.

Transportable ground stations that receive high data volumes from aircraft offer a solution for monitoring unforeseen events.

Bu çalışmada, zayıf türbülanslı atmosferde yayılan çoklu Gauss ışık hüzmelerinin Gauss formunda açıklığa sahip alıcı düzleminde oluşturdukları ortalama optik güç ve pırıldama indisi Huygens-Fresnel integrali kullanılarak analitik olarak yatay linkler için hesaplanmıştır. Özel olarak, Gauss, düz tepeli ve halkasal ışık hüzmelerinin türbülanslı atmosferde yayılımlarında alıcı düzleminde oluşturdukları ortalama optik güç ile pırıldama indisi, alıcı açıklık yarıçapı, yayılım mesafesi ve Gauss kaynak boyutu gibi parametrelere karşı incelenmiş, alıcı açıklık yarıçapının ortalama optik gücü artırmada ve pırıldama indisini düşürmedeki etkileri gözlemlenmiştir. Türbülanslı atmosferde yayılan düz tepeli ve halkasal ışık hüzmelerinin açıklık ortalama faktörü hesaplanmış, açıklık ortalama faktörü, alıcı açıklık yarıçapı, yayılım mesafesi ve Gauss kaynak boyutuna karşı çizdirilmiş, pırıldama indisini düşürecek değişkenler belirlenmiştir. Ortalama optik güç ve pırıldama indisi fonksiyonları amaç fonksiyonlar olarak belirlenerek Pareto-optimum eğrisi çizdirilmiş, ortalama optik güç ile pırıldama indisi arasındaki ilişki incelenmiştir. Ortalama optik gücün pırıldama indisine oranını en fazla yapacak şekilde belirlenen optimizasyon kriteri ile optimum Gauss, düz tepeli ve halkasal ışık hüzme modelleri belirlenerek link performans optimizasyonu yapılmıştır. Normalize optik güçteki düşmenin alıcı açıklık yarıçapının artırılmasıyla azaldığı görülmüştür. Açıklık yarıçapının artmasıyla ortalama optik güç artmakta, düz tepeli ışık hüzmeleri için düzleştirme parametresinin artırılmasıyla en fazla optik güç elde edilmekte ve halkasal ışık hüzmelerinde küçük yayılım mesafelerinde en fazla optik güç elde edilmektedir. Açıklık ortalama faktörünün etkisi, yapı sabitinin ve yayılım mesafesinin artmasıyla artmaktadır. Ayrıca, düz tepeli ışık hüzmelerinin yayılımında açıklık ortalamasının etkisi tüm açıklık yarıçap değerlerinde artan düzleştirme parametresi için artarken, halkasal ışık hüzmelerinin yayılımında büyük kaynak boyutu değerlerinde, büyük açıklık yarıçaplarında büyük ikincil hüzme kaynak boyutu değerlerinde artmaktadır. Belirlenen optimizasyon kriterine göre düşük kaynak boyutunda düşük yapı parametre değerleri için optimum çoklu Gauss ışık hüzmeleri elde edilmiştir. Ortalama optik gücün sintilasyona oranı sabit bir yapı sabitinde odaklanmış Gauss ışık hüzmeleri için artmaktadır. Bu oran sabit bir alıcı açıklık yarıçapında geniş halkaya sahip halkasal ışık hüzmelerinde artmaktadır. Düz tepeli ışık hüzmelerinde, sabit bir dalga boyu ve alıcı açıklık yarıçapı için düzleştirme parametresinin artırılmasıyla oran artmaktadır.Anahtar Kelimeler: Atmosferik yayılım, atmosferik türbülans, optik güç, pırıldamaindisi, optimum çoklu Gauss hüzme modeli, link performans optimizasyonu. In this study, the optical power and the power scintillation of multi Gaussian beams propagating in turbulent atmosphere is analytically calculated by using the Huygens-Fresnel integral when a realistic receiver possessing a finite sized aperture is employed in a horizontal atmospheric optics link. The optical power and the power scintillation of Gaussian, flat-topped and annular beams, as special cases of the multi Gaussian beam, is analyzed versus the receiver aperture radius, the propagation length and the Gaussian source size. The effect of the receiver aperture radius on the decrease of the power scintillation is examined. The receiver aperture averaging factor of flat-topped, annular beams are calculated and the receiver aperture averaging factors are plotted against the receiver aperture radius, the propagation length and the Gaussian source size. The link performance optimization is studied. Also the parameters that reduce the power scintillation index are found. The relation between the optical power and the power scintillation is analyzed by plotting the Pareto-optimum curve by defining the average optical power and the power scintillation as the object functions. An optimization criterion is defined as the maximization of the ratio of the average optical power to the power scintillation index from which the optimum Gaussian, flat-topped and annular beams are evaluated. The normalized optical power of the multi Gaussian beams decreases as the propagation length increases. The decrease in the normalized optical power reduces as the receiver aperture radius increases. The optical power increases as the receiver aperture radius increases and the increasing flatness parameter promotes the effect of the receiver aperture averaging on obtaining larger optical power for the flat-topped beams. However, for the annular beams, the maximum optical power is obtained at smaller propagation lengths. The effect of the receiver aperture averaging increases as the structure constant increases. Also, in the propagation of flat-topped beams the effect of the receiver aperture averaging increases as the flatness parameter increases for all receiver aperture radii. For the annular beams, the effect of the receiver aperture averaging increases for larger Gaussian source sizes, larger receiver aperture radii and larger secondary beam source sizes. At a fixed large propagation length, the flat-topped beams which have larger Gaussian source sizes have small power scintillation index. For the annular beams, smaller power scintillation is obtained for larger ring sizes. The ratio of the average optical power to power scintillation increases at a fixed structure constant for the focused Gaussian beams. The ratio increases for the annular beams which have larger ring sizes at a fixed receiver aperture radius. The ratio increases as the flatness parameter increases at fixed wavelength and receiver aperture radius for the flat-topped beams.Keywords: Atmospheric propagation, atmospheric turbulence, optical power, power scintillation index, optimum multi Gaussian beams, link performance optimization. 113

Uzun mesafeli kablosuz optik haberleşme bağlantıları için en önemli sorun, atmosferin sıcaklık ve basınç homojensizliğinden kaynaklanan atmosferik türbülanstır. Sönümlenme veya parıldama olarak da bilinen atmosferik türbülans, alınan optik sinyalin gücünde dalgalanmalara neden olmaktadır. Son yıllarda kablosuz optik haberleşme sistemlerinin performansını arttırmak için sönümlenme etkisini azaltmaya yönelik birçok teknik geliştirilmiştir. Bütün bu tekniklerdeki ortak varsayım, sadece alıcının kanal durum bilgisine sahip olması ve bu bilginin vericide mevcut olmamasıdır. Atmosferik türbülans sönümlenmeli kanallarda olduğu gibi çok yavaş değişen kanallar için, kanal durum bilgisinin alıcıda kestirilip geribesleme yolu ile vericiye gönderilmesi mümkündür. Verici bu bilgiyi kullanarak güç, modülasyon boyutu ve kodlama oranı gibi iletişim parametrelerini, bantgenişliği verimliliğini maksimize etmek için kanal durumuna göre değiştirebilir. Bu işlem, bağlantı uyarlaması olarak adlandırılmaktadır.Bu tezde, log-normal türbülanslı ve darbe konum modülasyonlu (pulse position modulation, PPM) kablosuz optik haberleşme sistemi için, tepe güç sınırı koşulu altında uyarlanabilir modülasyon ve kodlama teknikleri geliştirilmiştir. Özellikle üç teknik üzerinde çalışılmıştır: i) Kodlamasız kablosuz optik haberleşme sistemleri için uyarlanabilir modülasyon tekniği, ii) Kodlamalı kablosuz optik haberleşme sistemleri için uyarlanabilir modülasyon tekniği, ve iii) Modülasyon ve kodlamanın birlikte uyarlanması. Bu teknikler geliştirilirken sistemin verimliliğini tepe güç sınırı koşulu altında belli bir bit hata oranı ve devre dışı kalma olasılığı için maksimize eden optimal uyarlama stratejisi belirlenmiştir. Bilgisayar benzetim sonuçları, önerilen uyarlanabilir tekniklerinin uyarlanabilir olmayanlara göre daha iyi performans gösterdiğini kanıtlamaktadır. A major problem in long-range wireless optical links is atmospheric turbulence due to inhomogenities in the temperature and presure. This results in severe fluctuations of the received intensity of the optical signal, known as fading or scintillation. Over the last decade, various fading mitigation techniques have been proposed to improve the reliability of wireless optical links. A common assumption in all those techniques is that only the receiver has channel state information (CSI) while the transmitter has no knowledge of the channel. For very slowly-varying fading channels as in the case of atmospheric turbulence-induced fading, it is possible to reliably estimate the channel state information and send it back to the transmitter. The transmitter can use this information to vary the transmission parameters such as power, modulation size, code rate etc. according to the channel conditions. This is known as link adaptation. In this thesis, we investigate an adaptive modulation and coding scheme for wireless optical communication systems with M-ary pulse position modulation over log-normal turbulence channels under peak power constraints. Specifically, we consider three schemes: i) Adaptive modulation for uncoded wireless optical communicaiton systems, ii) An adaptive modulation scheme for coded wireless optical communication systems, and iii) Joint modulation and coding adaptation. Optimal adaptation strategy that maximizes the efficiency of the system at a targeted bit-error rate and outage probability under peak power constraint is determined. Our simulation results demonstrate significant performance improvements of the proposed adaptive schemes over non-adaptive counterparts. 77

Pointing, Acquisition and Tracking (PAT)-systems are one of the central parts of a Laser Communication Terminal. In Laser Communication Terminals a staggered PAT-system consisting of Coarse Pointing Assembly (CPA) and Fine Pointing Assembly (FPA) is common. The CPA provides a Wide-Field-of-Regard (FoR) and the FPA a precise and fast alignment of the beam to the communication partner. The disadvantage is the mechanical complexity. This paper presents the development challenges of a Wide-Field-of-Regard PAT-system for small Laser Communication Terminals by combining and miniaturizing the functionality of the CPA and FPA to a single actuator. To get a small and lightweight Wide-Field-of-Regard PAT-system, the number of moving parts has to be minimized. Therefore, the system consists of an optical setup that provides a large Field-of-View (FoV) and one single mirror actuator for beam steering – thus, CPA and FPA can be combined in just one moving component. The actuator is controlled by a Digital Signal Processor (DSP). The tracking sensor is a 4-Quadrants-Detector (4QD). During the acquisition mode, the actuator moves in a predefined scan pattern until a signal can be detected on the 4QD. Consequently, the system changes to tracking mode. Our design approach succeeded in a FoR of more than 45° without a traditional CPA. The scan time for the complete FoR is less than 1 second. The block diagram and measurements taken with the prototype in the laboratory will be presented in this paper.

This paper summarizes the results of a coherent transmission feasibility study which has been carried out for the coherent optical downlink from the German TerraSAR-X satellite. The receiver is located at an optical ground station. To evaluate the quality of the downlink experiment, effects of atmospheric refractive-index turbulence are investigated. By means of numerical simulations, the influence of turbulence on the communication system is analyzed. The simulated distorted complex field at the receiver is focused by means of a Fourier transform and superimposed on the local oscillator. The impact on the performance of a shot-noise-limited receiver is studied. This investigation showed that a mean bit error rate of 10-9 is achieved easily for all cases and turbulence conditions. The impact of phase-piston temporal fluctuations on the optical phase locked loop is investigated analytically. Beam motion with respect to the turbulence cells is taken into account. The calculated values for the additional residual phase noise due to the atmosphere are too small to cause significant deterioration of the receiver performance.

ÖZET Yüksek Lisans Tezi LAZERLI HABERLEŞME SİSTEMLERİNİN TASARIM PARAMETRELERİNE ÇEVRE VE ATMOSFER ŞARTLARININ ETKİLERİ ÜZERİNE ARAŞTIRMA B. Berna GÖGÜSGER Ankara Üniversitesi Fen Bilimleri Enstitüsü Elektronik Mühendisliği Anabilim Dalı Danışman: Doç. Dr. Faruk ÖZEK JürkDoç. Dr. Faruk ÖZEK Prof. Dr. Selçuk GEÇİM Prof. Dr. Abdulrza ABİLOV Bu çalışmada, çevre ışıması ve atmosfer şartlarının,serbest ortam optiksel iletişimde mobil sistemlerin tasarım parametrelerine etkisi araştırılmıştır. Sinyal/Gürültü oranının 72 olduğu durumda, maksimum iletim mesafesinin değişimi, değişik çevre ve atmosfer şartlan için gösterilmiştir. Lazer benek büyüklüğünün (çap) ve 4-Q dedektörlü ahcı üzerindeki pozisyonunun önemi gösterilmiştir. Hesaplamalarda iletim hızı 2,4-1 15,2kbps arasında alınmıştır. Gece etkili olabilecek,toprağın kendi İR emisyonundan kaynaklanan gürültü akımının etkisinin ihmal edilebilir olduğu hesaplamalarla ispatlanmıştır. Deniz uygulamaları incelendiğinden atmosferik zayıflatma katsayıları deniz seviyesinde seçilmiştir. Hesaplamalar ticari olarak bulunabilen sistem bileşenleri baz alınarak yapılmıştır. 1999,74 sayfa ANAHTAR KELİMELER: Optiksel iletişim, atmosfer etkileri, çevre ışıması, lazer benek büyüklüğü, maksimum iletim mesafesi, iletim hızı. ABSTRACT M.Sc. Thesis RESEARCH ON EFFECTS OF AMBIENT AND ATMOSPHERIC CONDITIONS TO DESIGN PARAMETERS OF LASER COMMUNICATION SYSTEMS B. Berna GOGUSGER Ankara University Graudate School of Natural and Applied Sciences Department of Electronics Engineering Supervisor: Assoc.Prof.Dr. Faruk ÖZEK Jury:Assoc Prof. Dr. Faruk ÖZEK Prof. Dr. Selçuk GEÇİM Prof. Dr. Abdulrza ABİLOV In this work, the effects of the ambient radiation and atmospheric conditions on the design parameters for mobile free space optical communication systems are investigated. Variations of the maximum communication range, at the signal -to- noise ratio 72,for different ambient and atmospheric conditions. The importance of the laser spot size and position on the receiver four-quadrant detector is depicted. Communication rates between 2,4 and 115,2kbps are considered in the computations. It is proved by calculation that by night the noise current due to the ground self infrared emission is negligible and only the dedector dark current is effective. Considering the on-sea applications, the atmospheric attenuation coefficients at sea level are chosen. Computations are based on the data for commercially available system components. 1999,74 pages KEY WORDS: Optical communication,free space,atmospheric effects, ambient radiation, laser spot size, max. communication range, communication rate. 74