Experimental Investigation of Optimum Beam Size for FSO Uplink

In this paper, the e ect of transmitter beam size on the performance of free space optical (FSO) communication has been determined experimentally. Irradiance pro le for varying turbulence strength is obtained using optical turbulence generating (OTG) chamber inside laboratory environment. Based on the results, an optimum beam size is investigated using the semi-analytical method. Moreover, the combined e ects of atmospheric scintillation and beam wander induced pointing errors are considered in order to determine the optimum beam size that minimizes the bit error rate (BER) of the system for a xed transmitter power and link length. The results show that the optimum beam size for FSO uplink depends upon Fried parameter and outer scale of the turbulence. Further, it is observed that the optimum beam size increases with the increase in zenith angle but has negligible e ect with the increase in fade threshold level at low turbulence levels and has a marginal e ect at high turbulence levels. Finally, the obtained outcome is useful for FSO system design and BER performance analysis.