NEW ORGANIC MATERIALS FOR HIGHLY EFFICIENT NONLINEAR OPTICAL SIGNAL PROCESSING

Abstract
Fiber optics communication systems, optical computing or industrial as well as scientific laser equipment include a number of nonlinear functions which, in turn, require new highly nonlinear materials to be adequately packaged in devices. Among these functions are electrooptic modulation, frequency mixing, parametric amplification and emission, and logical gating. As opposed to quasi-resonnant nonlinearities originating from confined structures and localized states such as in III-V compound nultiple quantum wells, the approach followed here is based on non-resonnant parametric nonlinearities originating from the interaction of light with highly delocalized π-electron polarizable systems (1). The efficiency is traded here for quasi instantaneous response and recovery times together with a wide-band tunability from the visible on to the infra-red. Prototype molecule and molecular systems will be discussed, exemplifying strategies where molecular charge transfer (optical diode-like) moieties are engineered so as to pack in centrosymmetric and possibly optimized (2) crystalline lattices. The properties of N-(4-nitrophenyl)-(L)-prolinol ("NPP") (3) and N-(4-nitrophenyl)-N-methylamino-acetonitrile ("NPAN") (4) will be emphasized and the parametric efficiency of these materials shown to be two orders of magnitude above that of Lithium Niobate. Other structures, such as Langmuir-Blodgett layers, organic cored fibers or nonlinear liquid crystalline polymers will be discussed and shown to open the way towards molecular waveguiding devices where the additionnal benefit of light confinement further enhances the gain.