Conception optique et hyperfréquence d'un modulateur électro-optique sur polymère : optimisation de transitions ultra-large bande pour l'électrode de commande

摘要

The electro-optical polymers are expected to allow realizing eventually cheaper modulators with better performances than those based on inorganic crystals such as LiNbO3 and semiconductors such as GaAs. This PhD thesis concerns the study and the design of the microwave and optical structure of a Mach-Zehnder modulator based on polymer, in order to demonstrate the feasibility of its realization based on the electro-optical polymer PIII (PGMA/DR1). The study of the optical structure using the software OptiBPM allowed, at first, to optimize the dimensions of the cross section of single mode with high confinement factor, so the absorption of the evanescent lightwave by the metallic electrode and the driving voltage of the modulator are minimized. The study of Y-junctions results in a trade-off between the losses by absorption of the polymer PIII and those by curvature, while keeping the minimum distance required between the two arms of the Mach-Zehnder interferometer, so the electrical field applied to one arm does not extend into the other one. In order to reduce the manufacturing cost of modulators and facilitate their characterization on chip with CPW probes, we studied especially ultra-broadband transitions coplanar microstrip (GCPW-MS) without via-holes and etching the ground plane. The results of measurements and simulations obtained using the software HFSS are in very good agreement for the transitions realized on both the commercial NH9338 substrate and polymer SU8 in thin layer of 8 µm. The simulations anticipate a bandwidth from 420 MHz to 60 GHz for a transition GCPW-MS-GCPW on polymer NOA61 in thin film with a metallization of silver of 6 µm.