Optical Telecommunication Paths (Lines)

The optical way of sending thru (transmitting) information has in general a multi-century history. Limiting ourselves to its modern parts, one can state that the first tests of optical communication were carried on at the end of the eighteenth century, when there was built in France (in accordance with the Chappe bros construction), a semaphore telegraph line connecting Paris with Lille. In the period that preceded the introduction of electrical telecommunication, optical communication was the fastest and most efficient way of reaching agreement over even very great distances. The development of the telegraph and telephone, guided and later unguided, pushed aside plans for the problem of optical communication. Only in special application, especially military, did communication on light waves in the infrared area maintain a certain importance (for instance in the course of the second world war optical telephone used to be used for communication over a range of from 3 to 15 km). The invention of the laser (in the year 1960) gave a powerful impulse to the renewal of investigations and experiments in the field of optical telecommunication, and the unattainable-to-this-time properties provided by the laser, of a light beam, (coherence, monochromaticity, and minimum divergence) dazzled the scientists and engineers abruptly by their dazzling prospects.