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COHERENT OPTICAL PROPAGATION STUDY.
ITT FEDERAL LABS NUTLEY NJ
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An integrated study is presented of the properties of optical laser propagation and radiation applicable to long range communication in both an atmospheric and free space environment. The results regarding the performance limitations imposed by the optical source as well as the medium can be summarized as Partial coherence of the laser causes a significant performance degradation when large simple receiving apertures are employed The lack of complete coherence is due, in part, to the presence of a multiplicity of cavity modes in the laser emission Some improvement can be expected from external mode locking techniques Coherent detection efficiency is markedly affected by mild atmospheric turbulence High detection efficiency can be obtained over very small apertures for paths on the order of 1 KM The use of a multiplicity of small apertures whose outputs are optimally combined appears to provide a means for achieving coherent optical communications over long atmospheric paths. Spectral distribution of the effect of atmospheric turbulence exhibits a 1f to the nth characteristic 2n1, therefore, the use of sub carrier techniques is indicated The use of both source and receiver aperture apodization is indicated for Fresnel region communication. Author
APPROVED FOR PUBLIC RELEASE