BORTOLOZZO , Umberto

We show experimentally that large matrixes of localized structures can be stored as elementary pixels in a nematic liquid crystal cell. Based on optical feedback with phase modulated input beam, our system allows to store, erase and actualize the localized structures in the matrix.

We study the Faraday instability in an elongated rectangular cell and for a range of the forcing frequency for which two nearly degenerate modes enter in competition. We investigate the stability properties of the two modes and we show that they can either coexist in a bistable way or give rise to a mixed mode. We develop a simple model based...

In a nonlinear optical experiment we report a unique class of localized structures, which appears as localized peaks of a pattern nucleating over another pattern. We show that this occurs when the system is driven through three pattern branches of solutions, accompanied by the appearance of localized peaks with two different amplitudes....

We show that the Talbot effect can be used to increase the gaib of two-wave mixing in a stack of this nonlinear media. We demonstrate that a large gain enhancement is achieved for a new nonlinear elements, provided that they are placed at distances that satisfy Talbot recurrences.

We show that the Talbot effect can be used to increase the gaib of two-wave mixing in a stack of this nonlinear media. We demonstrate that a large gain enhancement is achieved for a new nonlinear elements, provided that they are placed at distances that satisfy Talbot recurrences.

International audience

In a photorefractive liquid crystal light valve, acting as a Kerr-like nonlinear optical medium, we show the appearance of optical patterns induced by a single mirror feedback. The spatial wavelength of the patterns scales with the distance between the mirror and the valve and the contrast of the patterns decreases for decreasing this distance....

Liquid-crystal (LC) optically addressable spatial light modulators (OASLMs) allow control of the phase and amplitude of optical beams. By performing wave mixing in an OASLM, we show that coherent phase detection can be achieved for light beams passing through highly scattering media, such as foam layers with several cm thicknesses. Thanks to...

International audience

International audience

We perform jointly spectral and spatial characterization of cholesteric liquid crystals with oblique helicity through a liquid crystal-based hyperspectral imaging, which is a compact and non-destructive technique ideally adapted to characterize mesoscopic samples, both in transmission and reflection.

International audience

Electrically driven nematic liquid crystals layers are ideal contexts for studying the interactions of local topological defects, umbilical defects. In homogeneous samples the number of defects is expected to decrease inversely proportional to time as a result of defect-pair interaction law, so-called coarsening process. Experimentally, we...

International audience

Ongoing research on chiral liquid crystals takes advantage of the peculiar behavior of twisted structures subject to curvature. We demonstrate the fine tunability of the characteristics of the bandgap of a cholesteric structure in which the orientation of the helix axis spatially changes. To date, the spectral resolution of the order of 6 nm,...

International audience

International audience

International audience

Hyperspectral imaging collects knowledge about the spectral content enclosed in a given target. For such investigations , fundamental requirements include the ability to extend the spectral range, improve the spectral resolution, and achieve a large field of view together with compactness and robustness. Here we introduce a new method of...

International audience

We present an unifying description of a new class of localized states, appearing as large amplitude peaks nucleating over a pattern of lower amplitude. Localized states are pinned over a lattice spontaneously generated by the system itself. We show that the phenomenon is generic and requires only the coexistence of two spatially periodic...

International audience

We simplify, to first order in v c , the generalized, special relativistic treatment of a Doppler shift from an arbitrarily translating mirror originally derived by Ashworth and Davies [ Proc. IEEE 64 , 280 ( 1976 ) IEEPAD 0018-9219 10.1109/PROC.1976.10098 ]. We show that it is in good agreement with a somewhat modified, but more intuitive,...

A nonlinear optical medium results by the collective orientation of liquid crystal molecules tightly coupled to a transparent photoconductive layer. We show that such a medium can give a large gain, thus, if inserted in a ring cavity, it results in an unidirectional optical oscillator. Dynamical regimes with many interacting modes are made...

A dynamical optical characterization of planar nematic liquid-crystal cells electrically driven through the Fréedericksz transition is presented. Our method involves applying voltage steps with different starting voltage close to the Fréedericksz threshold. Measurements are performed on cells with various thickness, from a few microns up to...