Survey of near infra-red communication systems.

The development of methods of communication by means of light beams is reviewed from the work of A. G. Bell in 1880 to the termination, in 1945, of the activities carried out under the auspices of the Office of Scientific Research and Development. The review is limited to voice and code systems, and includes a discussion of methods of producing modulated beams of radiation, use of filters to provide security in military applications, and a summary of the various types of photo-sensitive receiving elements used. An attempt is made to correlate the factors responsible for the trend of developments during each period and to evaluate the relative merits of the several types of systems which have been studied. Descriptions of several types of foreign light-beam communication equipments are included. An extensive bibliography has been compiled.