On aperture averaging of speckle patterns

Statistical parameters of the power of a nonuniform (speckled) light field measured by a photodetector with a finite receiving aperture were investigated. Such a field was created by passing coherent laser radiation through a multimode optical fiber and then scanned across the aperture. It was demonstrated that the mean square deviation of the received power is defined by a parameter equal to the ratio of the aperture diameter to the characteristic dimension of the spatial variations of the light field. If this ratio is more than 2, the above deviation does not exceed values permissible for devices using spatially coherent light (e.g., for free-space optical communication systems). (C) 2003 MAIK "Nauka/Interperiodica".