Wavelength Correlation in Free Space Optical Communication Systems

Free space optical (FSO) communication systems are attractive for the military because such systems are capable of transmitting extremely high data rates over very long point-to-point links. However, in the presence of atmospheric turbulence the FSO channel will be distorted and this limits the effective data rate that can be transmitted over the link. These distortions can affect the signal in the spatial, time and wavelength (frequency) domains. It is well known that channel coding and diversity techniques can be employed to mitigate the channel distortions and improve the performance of the communication link. For these techniques to be effectively utilized the FSO channel properties have to be characterized. In this paper we will examine the correlation of the FSO channel across wavelengths under the weak turbulence propagation model. Specifically, we will determine the wavelength correlation of the FSO signal for the satellite-to-ground and ground-to-satellite links with coherent and direct detection schemes