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Frontiers of Optoelectronics

ISSN 2095-2759

ISSN 2095-2767(Online)

CN 10-1029/TN

Postal Subscription Code 80-976

Front Optoelec Chin    2009, Vol. 2 Issue (3) : 312-317    https://doi.org/10.1007/s12200-009-0030-z
RESEARCH ARTICLE
Effects of light propagation in middle intensity atmospheric turbulence
Mzee S. MNDEWA(), Xiuhua YUAN, Dexiu HUANG, Bangxu LI
Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
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Abstract

The purpose of this report is to present an experimental study of the effects of light propagation through atmospheric turbulence. Free space optical communication is a line-of-sight technology that transmits a modulated beam of visible light through the atmosphere for broadband communication. The fundamental limitations of free space optical communications arise from the environment through which it propagates. However these systems are vulnerable to atmospheric turbulence, such as attenuation and scintillation. Scintillation is due to the air index variation under the temperature effects. These factors cause an attenuated receiver signal and lead to higher bit error rate (BER). An experiment of laser propagation was carried out to characterize the light intensity through turbulent air in the laboratory environment. The experimental results agree with the calculation based on Rytov for the case of weak to intermediate turbulence. Also, we show the characteristics of irradiance scintillation, intensity distribution and atmospheric turbulence strength. By means of laboratory simulated turbulence, the turbulence box is constructed with the following measurements: 0.5 m wide, 2 m long and 0.5 m high. The simulation box consists of three electric heaters and is well described for understanding the experimental set up. The fans and heaters are used to increase the homogeneity of turbulence and to create different scintillation indices. The received intensity scintillation and atmosphere turbulence strength were obtained and the variation of refractive index, with its corresponding structure parameter, is calculated from the experimental results.

Keywords free space optical communication      atmospheric turbulence      scintillation     
Corresponding Author(s): MNDEWA Mzee S.,Email:mndewa@excite.com   
Issue Date: 05 September 2009
 Cite this article:   
Mzee S. MNDEWA,Xiuhua YUAN,Dexiu HUANG, et al. Effects of light propagation in middle intensity atmospheric turbulence[J]. Front Optoelec Chin, 2009, 2(3): 312-317.
 URL:  
https://academic.hep.com.cn/foe/EN/10.1007/s12200-009-0030-z
https://academic.hep.com.cn/foe/EN/Y2009/V2/I3/312
Fig.1  Experimental set up. (a) Laser beam set up; (b) turbulence box set up
Fig.2  Theoretical attenuation of 632.8 nm against visibility by using Eqs. (3) and (5)
Fig.3  Comparison of attenuation between laser wavelengths 632.8 and 1550 nm
Fig.4  Behavior of light beam when passes through turbulence box while fans are switched off
Fig.5  Behavior of light beam when passes through turbulence box while fans are switched on
Fig.6  Behavior of light beam when passes through turbulence box while fans are switched on (second trial)
Fig.7  Behavior of light beam when passes through turbulence box while fans are switched off (second trial)
eventscintillation indexrefractive index structure parameter / m-2/3
no turbulence0.30294.55×10-11
turbulence1.13391.70×10-12
no turbulence0.14202.13×10-11
turbulence0.00701.15×10-10
Tab.1  Calculation of refractive index structure parameter from experimental results
Fig.8  Irregularity of beam intensity distribution in laser beam that has passed through 2 m of non-simulated atmospheric turbulence (pictures are taken with a time interval of 2 min)
Fig.9  Irregularity of beam intensity distribution in laser beam that has passed through 2 m of simulated atmospheric turbulence (pictures are taken with a time interval of 2 min)
Fig.10  Spatial intensity distribution in laser beam that has passed through 1 km of atmosphere with weak turbulence (pictures are taken with a time interval of 2 ms)
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