Application of LASERS to Digital Communications

Revolutionary developments taking place in the field of light generation show promise of providing a means for transmitting digital information over vast distances in space at extremely high rates. These developments stem from the generation of coherent light by devices called LASERS (Light Amplification by Stimulated Emission of Radiation). This paper gives a brief description of LASER operation and discusses the applicability of the device to certain aerospace vehicular digital communications requirements. An earth-moon link is an alyzed from the standpoint of beamwidth, power, and aiming requirements. It is shown that a system utilizing a coherent optical transmitter of less than 1 w and a conventional photodetector would be capable of transmitting digital information over this link at megacycle rates. The bandwidth limitation here is imposed by lack of a suitable modulator rather than by any theoretical bound, and the power level is dictated by earth background noise and a usable transmitter and receiver beam angle. Improvements which can be made on this rather simple system by increasing bandwidth and improving detection efficiency, tracking accuracy, and LASER techniques are pointed out. Curves showing basic limitations and interdependence of system parameters are plotted.