LASER COMMUNICATIONS STUDY.

Abstract : The design of a laser communications system was predicated upon obtaining a tool with which the deleterious effects of the atmosphere on a FM signal could be measured. The system incorporates the elements of a coherent communications system with sufficient bandwidth to handle a 12 voice channel binary multiplex. Modulation of the light is accomplished in the UHF region. This is a 'single-ended' system (i.e. a mirror is used at one end) utilizing a single laser to provide LD and signal beam power. The system design was implemented during the development phase. A two-element electro-optic modulator enclosed in a UHF cavity to obtain the desired frequency translation is described. In an additional operational mode the carrier is not suppressed and the 'local oscillator' is transmitted with the signal. Atmospheric path study tests showed both modes were at times greatly degraded by atmospheric turbulence. This is primarily attributed to thermal gradients in the atmosphere. The heterodyne signal degraded more than the 'self-mix' (carrier plus sideband) mode. (Author)