平成２１年度　実績報告書

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教育研究プラットフォームIDER研究成果/ポストドクター・GCOE研究員Investigation of Optical Scintillation Characteristics for Free Space Optical Link Design Kyung - Hwan Kim D ivision of Electrical, Electronic and Information Engineering , Graduate School of Engineering , Osaka University Ko maki Laboratory Abstract Optical scintillation can significantly impair the performance of free space optical (FSO) links. Investigation on its characteristic is required to construct a FSO link, and directly related to design of optical link margin. This report presents an example of empirical characteristics of optical scintillation base on analysis of several experiment data of FSO link. FSO technology can provide easy - to - install and high - speed links for various radio services. Recently, radio on free space optical (RoFSO) system [1], which is the convergence of radio on fiber (RoF) and FSO technologies, has developed to realize a cost - effective and universal platform for heterogeneous radio services. Since they includ e the optical propagation through the atmosphere, signal transmission qualities are affected by optical scintillation. In general, optical scintillation is characterized by variance and frequency. Variance is directly related to optical loss and frequen cy is closely related to fade duration, determining auto gain control (AGC) performance. Especially, Tatarski [2] presents the relation of frequency characteristic of optical scintillation and wind speed component normal to an optical path. However, this m odel is not proper to evaluation or optimum design of such systems since his theory accounts for the relation only. In this report, presents empirical ranges of the two parameters of optical scintillation obtained experiment data of FSO link. Fig ure 1 dep icts the experimental configuration. The length of optical path is 1km. After 785 nanometers beam is radiated from the Tx, received beam intensity is converted to photocurrent, i ( t ) . Then, it is sampled and obtained i ( kT ) , k =0 , 1 , 2 , ... , where T =0 . 0001 sec. Finally, the parameters of optical scintillation are extracted from the data by a time - correlated process, which enables us to treat scintillation frequency by f c [1]. Fig ure 2 shows a distribution chart of and f c . In the figure, the total number of point is about 1,500. Their ranges can be found to about σi 2 of 0 to 0.26 and f c of 0Hz to 180Hz, respectively. It can be assumed that two parameters of 0 all in the case of without scintillation. The correlation coefficient between the two parameters is close to zero. It is observed that almost and f c are distri buted over 90 percents of all present below 0.1 and 80Hz, respectively. Fig. 1 Experimental Configuration Fig. 2 distribution chart of and f c References [1] K. Kim, et al., “Statistical Analysis on the Optical Fading in Free Space Optical Channel for RoFSO Link Design,” Proc. of SPIE , Vol. 7620, pp. 7620OL1 - 10, 2010. [2] V. I. Tatarski, Wave Propagation in a Turbulent Medium , McGraw - Hill, NY, 1961. σi 2 σi 2 σi 2 σi 2 93

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