Abstract

The efficiency of nonlinear effects in bulk materials and integrated optics is constrained by phase matching relations between the different waves interacting inside the medium. Artificial control of the phase mismatch between the different waves in interaction can be achieved by periodic 1D or 2D patterns of the susceptibility or refractive index, known as quasi phase matching gratings. Soft and amorphous materials like polymers are therefore appealing for designing adequate structures to fulfill the phase-matching condition. This can be done with optical techniques enabling to process arbitrary 2D nonlinear structures down to micron scale resolution. Nonlinear optical molecules such as Disperse Red 1 exhibit photochemical sensitivity which enable them to be reoriented under irradiation by light [1,2]. More specifically, when a film is irradiated by a linearly polarized light beam, the molecules tend to align perpendicularly to the beam polarization, which results in an axial biréfringent order known as the Weigert effect. Irradiation of an ensemble of previously oriented molecules erases the initial order leading to the adequate axial non centrosymmetric alignment. We therefore use this technique for encoding various structures by means of a holographic grating recording configuration (Fig. 1) or by using different masks (Fig. 2). Sample characterization was then performed both by polarized microscopy, by scanning non linear optical polarization microscopy and by Atomic Force Microscopy (Fig. 3). The definition of the mask then enables to define various structures with resolutions limited by the Rayleigh criterion as in photolithography. Further use of all optical poling techniques [2] enables direct writing of non linear optical susceptibilities by optical means, allowing full control of the tensorial properties of the locally patterned nonlinear optical susceptibility tensor (Fig. 4).

© 2001 EPS