Research On Transmission Performances Of Atmospheric Laser Communication System With Different Wavelengths

Free Space Optical(FSO)communication has attracted considerable research interest in the telecommunications fields due to its large bandwidth,high transmission rates,and other attractive features.Unfortunately,the randomness of the characteristic of atmospheric transmission channel limits its application.Thus,how to reduce the influence of the atmosphere on the laser transmission to improve the transmission performance is important for the FSO system.In this paper,the effects of atmosphere on the FSO system with different wavelengths are studied,the results can provide some scientific basis and technical support for the development of long-wavelength FSO communication technology.Firstly,this work analyzes the influence of atmospheric attenuation,which is divided into atmospheric absorption and atmospheric scattering on laser transmission.Some specific laser wavelengths are found more suitable for the FSO system because their attenuation values are less than those of other wavelengths.Secondly,the Fast Fourier Transform based subharmonic method,is used to numerically simulate the atmospheric turbulence.The optimal subharmonics selection for atmospheric turbulence phase screen simulation with a given precision using this method is investigated.To precisely determine the optimal subharmonics required for simulation,a criterion called a structure function increment ratio is presented and the integrated power ratio criterion is improved.Based on the above two criteria,the optimal subharmonic numbers which should be added in the simulation for different atmospheric turbulence phase power spectral density models are calculated.Furthermore,the phase structure function and relative error function are employed to evaluate the accuracy of the obtained optimal subharmonic levels.Finally,the transmission performances of the laser with different wavelengths transmitted through the atmosphere are compared.The results demonstrate long wavelength is more suitable for FSO system.To make the FSO system work for the long wavelength,only additional two wavelength converters need to be added into the current FSO system working in 1550 nm wavelength.But in this way,the transmission performance of FSO can be effectively improved.