SILEX: The first European optical communication terminal in orbit

Optical communication is presently in a rapid expansion phase, since it off ers a considerable growth potential to the constantly increasing useful tra nsmitted data rate demand. Planned constellations of communication satellit es will benefit from the use of optical communication's ability to transmit the increasingly higher data rates with compact, low-mass terminals, while avoiding interference problems and radio frequency band saturation. in add ition to semiconductor lasers and highly sensitive wide bandwidth optical c ommunication sensors,optical communication implies utilisation of a wide ra nge of leading-edge technologies, e.g, ultrastable structural materials, hi gh-precision pointing mechanisms, large CCD matrices, fast digital signal p rocessing, high precision optics, optical coatings with high reflectivity o r narrow filter bandwidth and accurate thermal control. In 1991 the development phase of an optical communication system, SILEX (Se mi-Conductor Inter Satellite Link EXperiment) was started with MMS (F) as p rime contractor leading a large European consortium. The step from the optical bench in the laboratory to an optical terminal in orbit is enormous. This step was achieved when PASTEL (PASsager TELecom) o n SPOT-4 was successfully launched on 22 March 1998.