Transmission d'images par modulation du spectre

Abstract

In this paper, we describe an all-optical method of transmission of the information contained in a photographic transparency. The basic principle consists of modulating, by a one-dimensional transparency, the spectral density of a wide-band collimated light beam, which can be transmitted over several kilometres. The image of the photographic transparency is obtained by simply displaying the optical spectrum of the received light beam. As all resolvable details of the one-dimensional image are transmitted in parallel, this method makes it possible to reach a high information rate. We also show experimentally how a two-dimensional image can be reconstructed. The theoretical and practical limits to the transmission capacity of the system are analysed, and an information rate of 20 Mbits/s appears readily obtainable. The performance of this method compares advantageously with that of two other methods of wide-band light–wave communication (Delisle et Cielo; Froehly, Lacourt et Vienot). We also describe an experimental technique for correcting the problems arising from the wavelength-dependent absorption of the propagation material and the chromatic selectivity of the photographic emulsion. Finally, we emphasize the potential applications of this method in the area of computer to computer communication.