Suppression of scintillations and beam wandering in free space gigabit rate optical communication based on spectral encoding of a partially coherent beam

A new concept of a free-space, high-speed optical communication (FSOC) system based on spectral encoding of radiation from a broadband pulsed laser is developed. It is known that the intensity fluctuations of a partially coherent beam in combination with a time-averaging photodetector leads to a significant scintillation reduction with the corresponding improvement of the bit error rate by several orders of magnitude. Unfortunately, the time-averaging method cannot be applied directly to gigabit data rate communication. The main limitation of this method is related to the requirement that the correlation time between different spatially coherent spots be shorter than the response time of the photodetector. We propose to extend the technique of scintillation suppression, based on time averaging of a partially coherent beam, to gigabit data rate FSOC. In our approach, information is encoded in the form of amplitude modulation of the spectral components of the laser pulse which has a broad spectrum. To examine the intensity fluctuations of a partially coherent beam under the conditions of strong turbulence, we developed an asymptotic method for solution of the kinetic equation for the photon distribution function. We show that, for long distances, scintillations and beam wandering can be significantly suppressed.