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Scintillation is an effect that limits the performance of many optical systems including imagers and free space optical communication links. Scintillation can be especially severe for optical retro-reflectors. This can limit the range of links based on modulating retro-reflectors. In this work we examine the effects of retro-reflector diversity on optical scintillation. This technique uses multiple retro-reflectors, separated by a distance larger than the atmospheric coherence size and illuminated by one interrogating beam, to reduce the scintillation index. We examine the dependence of scintillation index on the number of retro-reflectors, their separation and the degree of coherent interference at the receiver.

Data was taken in the field at three different sites: the Naval Research Laboratory's Chesapeake Bay Detachment, where both over land and over water measurements were made, the Fort AP Hill Laser Test Range and China Lake, California. We show that multiple retro-reflectors can reduce the scintillation index on double-pass links. We demonstrate that when retro-reflectors are spaced too closely, coherent interference can increase the scintillation index and greatly expand its frequency content. We also examine the effects of retro-reflector diversity on the margin needed for modulating retro-reflector data links.