19710

۱۹۷۱۰

بررسي و شبيه سازي تاثيرات پديده هاي اتمسفري بر رفتار انتشار مورب باريكه هاي ليزري در مخابرات بي سيم نوري

دكتري تخصصي

فيزيك اتمي مولكولي

۱۳۹۲

۱۳۹۷/۸/۱۵

دكتر بيژن غفاري قمي

فيزيك

در پايان نامه حاضر، با توجه به نقش تضعيف¬كننده و مخرب تلاطم اپتيكي و مهمترين اثر آن يعني پديده سوسوزني در كارايي و كيفيت لينك¬هاي ارتباطي اپتيكي اتمسفري و لزوم مطالعه جامع تلاطم اتمسفري در شرايط آب و هوايي مختلف با احتساب انتشار مورب در اتمسفر متلاطم و به منظور بهره¬برداري از مزاياي بالقوه اين¬گونه سيستم¬ها، به مطالعه و شبيه¬سازي اثر تلاطم اپتيكي بر مهمترين پارامترهاي يك لينك مخابرات ليزري پرداخته شده¬است. با توجه به اين نكته كه تلاطم تنها پديده موثر در لينك¬هاي مخابراتي اتمسفري نيست و جذب و پراكندگي هم در تعيين عملكرد لينك¬هاي مخابراتي به خصوص در بودجه بندي لينك نقش مهمي دارد، تاثيرات مخرب اين دو پديده اتمسفري نيز با استفاده از مدل لوترن(Lowtran) در اين پايان¬نامه مورد مطالعه قرار گرفته¬اند. جهت نيل به اين اهداف، دو گام اساسي برداشته شده¬است. در گام اول بر اساس روش انتگرال تعميم يافته¬ي هويگنس- فرنل، ابتدا اثر تلاطم اپتيكي بر رفتار انتشاري مشخصه¬هاي آماري و اپتيكي باريكه¬هاي ليزري آرايه¬اي با پروفايل سرصاف از جمله توزيع شدت، عرض باريكه، درجات قطبش و همدوسي و فاكتور كيفيت M2 به صورت تحليلي بررسي شده و سپس با شبيه¬سازي عددي پديده¬ي سوسوزني، تأثير آن بر پارامترهاي كيفيت لينك مخابراتي مانند خطاي بيت و نسبت سيگنال به نويز مورد مطالعه قرار گرفته¬است. در گام دوم، بر اساس قانون بيرلامبرت و به كمك مدل لوترن (Lowtran) پديده¬هاي جذب و پراكندگي در اتمسفر شبيه¬سازي شده و سپس تاثير اين پديده¬هاي تضعيف كننده بر پارامترهاي لينك مخابراتي مانند توان در واحد سطح، خطاي بيت و نسبت سيگنال به نويز مورد بررسي و مطالعه قرار گرفته¬است. اميد است بر اساس نتايج مطالعات صورت گرفته در اين رساله و اهميت روز¬افزون مخابرات نوري به خصوص در ارتباطات ماهواره¬اي، در درجه اول گام مـؤثري در بومي¬سازي فن¬آوري مخابرات نوري و سپس جهت بهبـود عملكرد لينك¬هاي مخابرات ليزري اتمسفري در شرايط آب و هوايي مختلف برداشته¬شود.

1397/09/09

Theoretical Investigation of Atmospheric Effects on the Slant Propagation Behavior of Laser beams in Wireless Optical Communication Links

12/1/2018 12:00:00 AM

After the invention of laser in 1960, the introduction of laser and the significant advances made in its production with various characteristics, as well as the possibility of using it in a variety of strategic applications such as the data transmission, commercial and defense optical communication, on the other hand to make extensive research on the use of laser beams as an data transmission agent in the applications. Often, these applications, which include optical communications, satellite communications, remote sensing, Lidar, Ladar, imaging, communication links between ships and the beach, positioning, and targeting are based on the propagation of laser beams in randomly changed refractive-index (optical turbulence) such as the atmosphere. Since communication theory is based on sending, transmitting and receiving data, it is important to study the effects of the propagation media as a communication channel on optical laser beams. Three fundamental phenomena that affect the propagation of optical waves in random media include absorption, scattering and turbulence (fluctuation of the refractive index). In all applications, in order to design and characterize more precisely, along with the phenomena of absorption and dispersion, the various effects of the oppressive phenomenon of optical turbulence, such as broadening, decreasing the degree of coherence and polarization, wandering of rays and intensity fluctuations on the electromagnetic wave field in the atmosphere are also considered in calculations, simulations and studies. Therefore, considering the destructive role of optical turbulence and its most important effect, namely the phenomenon of scintillation on the efficiency and quality of the atmospheric optical link communication, and the need for a comprehensive study of atmospheric turbulence in different climatic conditions, taking into account the slant propagation in the turbulent atmosphere and in order to capitalize on the potential benefits of such systems, this thesis studies and simulates the effect of optical turbulence on the most important parameters of a laser communication link. Considering the fact that turbulence is not the only phenomenon affecting atmospheric communication links, the absorption and scattering also play a significant role in determining the performance of communication links, especially in link budgeting. The destructive effects of these two atmospheric phenomena, also using the model Lowtran have been studied in this thesis. To achieve these goals, two basic steps have been taken. In the first step, based on the generalized Huygens-Fresnel integral method, the effect of optical turbulence on the propagation behavior of the statistical and optical characteristics of Flat-topped array laser beam such as intensity distribution, beam width, polarization and coherence and beam quality factor (M2-Factor) were analyzed analytically and then, by simulation of the scintillation phenomenon, its effect on the parameters of communication link quality, such as Bit Error Rate (BER) and Signal to Noise Ratio(SNR), has been studied. In the second step, according to the law of Beer-Lambert and with the help of the Lowtran model, atmospheric absorption and scattering phenomena are simulated, and then the effect of these destructive phenomena on the communication parameters such as Power In Bucket (PIB) , BER and SNR has been studied. In recent years, laser introduction and significant developments in its generation with different characteristics besides the possibility of its usage in various applications of wireless data communication in one side and ever-increasing human need to the more bandwidth for transferring any kinds of data in another side, lead to the vast research in the field of laser beam usage as a data carrier in strategic applications such as optical communication, satellite communication, Lidars, remote sensing, imaging, underwater communication, marine exploration and research, targeting and navigation. It is hoped that, based on the results of the studies carried out in this thesis and the importance of optical communications, especially in satellite communications, this thesis is primarily an effective step in the localization of optical communication technology and then to improve the performance of this technology in different weather conditions.