Contribution à la Conception de Capteurs Electrooptiques de Champ Electromagnetique

Abstract

With the progress realized in domains as the aeronautics, appeared the possibility to embark devices of communication on planes, on cars etc.... The idea to use the technology of microstrips as antennas allowed to bring solutions to the question of the congestion of these devices. However, the used techniques of supply by welded coaxial cable on the antenna or by microstrips, perturbs the radiation of the antenna. Furthermore, to limit the attenuation of the radio frequency signal and the disturbances, the chain of signal processing must be close to the antenna. A solution of this problem is to use the optical domain. In fact an optical fiber is transparent to the radio frequency radiations and then do not perturb the antenna. On the other hand, the losses in a fiber are of an order which is less than the losses in the wave guide, what allows to take away the chain of data processing. The applications are multiple: sensors of fields, radar system fed by optical way, and receivers of telecommunication at moderate costs. To realize the optical / electric conversion the most successful material is Lithium Niobate but its high dielectric constant limits the bandwidth of any device. The polymer materials are to supplant it, at present,. The electromagnetic waves got by a system of reception, perturbs directly the electro-optical material and modify by Pockels effect its index and thus the speed and the polarization of the light wave which crosses it. The system of microwave reception that must allow the increase of the electric field interacting with the material; a structure like patch antenna is examined. The spectral method is applied to estimate the electric field in the anisotropic multilayer material. We show that for substrate with organic materials (with losses and of small thickness), this structure cannot be used, a dipole antenna structure is better adapted.