Data Transmission At Optical Frequencies

System analysis of an optical data transmission link and the basic expressions for beam power, received power and signal-to-noise ratio are derived. It is shown that transmission at optical frequencies requires 3-4 orders of magnitude less power than at K band. The effect of background noise, such as sunlit earth, on the signal-to-noise ratio and the improvements obtained by limiting the receiver look-back angle and use of narrow band optical interference filters are considered. In addition, a summary of the design parameters and the problems that were encountered during the development and testing of the Optical Data Transmission System are presented. The system capabilities are given and the successful transmission of a closed circuit television picture over a 2-mile path with a 33 db signal-to-noise ratio is discussed. Atmospheric effects on transmission and the results of a 33 db attenuation of signal over a 2-mile path during a heavy snow storm with 1/4 mile maximum visibility are given. Finally, a comparison of the Gallium Arsenide light emitting diode and the Gallium Arsenide laser diode is presented. It is shown that for otherwise identical systems the beam power is increased by 30 db over the noncoherent system