Overview of the FASOLT Experiment and Final Results"

Kurzfassung

Within the frame of the FASOLT project the German Aerospace Center (DLR) performed channel measurements and optical data transmission tests on a 61 km near ground horizontal path. The transmitter was situated on a mountain top in the German Alps with the receiver placed on top of a building at the DLR site in Oberpfaffenhofen. Partners in the FASOLT project were Contraves Space, Switzerland and EADS Military Aircraft, Germany. During a period of several months various data sets of scintillation data were recorded in one and two laterally separated transmitter configurations and under different environmental conditions. A significant decrease of number and depth of fades was observed for the two transmitter setup. This paper presents an overview on the scintillation statistics of this particular optical channel. Also beam offsets due to refraction have been measured and results are presented here. As well as these measurements, data transmission tests at bit rates of 100 Mbps have been performed. A two transmitter configuration with a transmit power of 1 W per laser and a sensitive APD receiver front-end plugged in to a 75mm Rx telescope have been used. Despite severe scintillations, bit error rates (BER) below 1e-4 could be observed, though synchronization losses of the data and clock recovery affected the results. Tests at 155 Mbps (OC-3) and 270 Mbps (SMPTE 259M) were not successful due to high atmospheric attenuation. This paper gives an overview of the entire experimental setup, sums up the results of this long-haul data transmission experiment, and gives an outlook to further DLR activities in the field of free-space optics.