S. Residori

Non-Gaussian Statistics and Extreme Waves in a Nonlinear Optical Cavity

A unidirectional optical oscillator is built by using a liquid crystal light valve that couples a pump beam with the modes of a nearly spherical cavity. For sufficiently high pump intensity, the cavity field presents complex spatiotemporal dynamics, accompanied by the emission of extreme waves and large deviations from the Gaussian statistics. We identify a mechanism of spatial symmetry breaking, due to a hypercycle-type amplification through the nonlocal coupling of the cavity field.

Roll-hexagon transition in a Kerr-like experiment

A transition between hexagons and rolls is observed in an optical diffractive system containing a LCLV acting as a Kerr-like non-linearity. A rotation of 180° in the optical feedback is responsible for the appearance of new stable structures as negative hexagons and rolls. The stability of the different patterns is discussed by means of a simple model based on coupled normal form equations.

Soliton gating and switching in liquid crystal light valve

Using a photoconductive light valve with nematic liquid crystals, we introduce a versatile platform for the excitation and routing of spatial optical solitons, with external beams controlling the whereabouts of the underlying all-optically induced waveguides and their spatial dynamics. Using this all-optical control of soliton trajectory, we demonstrate a NOR gate, an XNOR, and a Boolean half-adder.Using a photoconductive light valve with nematic liquid crystals, we introduce a versatile platform for the excitation and routing of spatial optical solitons, with external beams controlling the whereabouts of the underlying all-optically induced waveguides and their spatial dynamics. Using this all-optical control of soliton trajectory, we demonstrate a NOR gate, an XNOR, and a Boolean half-adder.

Optical wave turbulence and the condensation of light

In an optical experiment, we report a wave turbulence regime that, starting with weakly nonlinear waves with randomized phases, shows an inverse cascade of photons toward the lowest wavenumbers. We show that the cascade is induced by a six-wave resonant interaction process and is characterized by increasing nonlinearity. At low wavenumbers the nonlinearity becomes strong and leads to modulational instability developing into solitons, whose number is decreasing farther along the beam.

Nematicon all-optical control in liquid crystal light valves

We discuss the interactions between self-guided light beams and light-induced perturbations in a liquid crystal light valve. The model and data are in perfect agreement.

Beam coupling in photorefractive liquid crystal light valves

Photorefractive liquid crystal light valves (LCLVs) are hybrid devices that combine a nematic liquid crystal layer with a thin monocrystalline Bi12SiO20 (BSO) photorefractive crystal in the form of a cell wall. The device behaves as an optically addressed spatial light modulator, where the photoconductive layer is made of the BSO crystal. Differently from conventional types of spatial light modulators, usually working in retroreflective configuration, the photorefractive light valves work in transmission, thus allowing new applications related to the coupling of the optical beams when they pass through the liquid crystal layer. Here, we review some recent experiments of beam coupling in photorefractive LCLVs. After a characterization of the device in terms of its spatial resolution, which is related to the features of pattern formation in an optical feedback configuration, we present two-beam coupling and optical amplification in single pass experiments. Then, we develop a theoretical model by taking into account the Raman–Nath diffraction of the incoming beams over the thin liquid crystal layer. By using two or more light valves in cascade, we show, both experimentally and theoretically, that the two-wave mixing gain can be enhanced by the Talbot effect related to the multi-passage of the beams through the successive layers of the nematic liquid crystal. Finally, we show that self-pumped phase conjugation can be realized by placing the light valve in a tilted feedback configuration. In this case, the four-wave mixing is spontaneously created through the scattering of the signal beam onto the feedback induced grating.

Mid-IR to near-IR image conversion by thermally induced optical switching in vanadium dioxide

We demonstrate the image conversion from mid-IR to near-IR (NIR) exploiting high-contrast optical switching in vanadium oxide thin-film layers. The intensity distribution of a mid-IR beam is converted to NIR wavelengths exploiting the strong reflectivity changes induced by optical pumping in the mid-IR. We show an experimental setup in which the radiation of a Tm-doped fiber laser at 1940 microm and a carbon dioxide at 10.6 microm has been converted to both 850 nm and 1064 nm. The resolution was 35 microm and was reached by using an inexpensive CCD camera. The sensitivity of the device increases linearly with sample temperature. We measured a threshold of 144 mW/cm(2), with a sample temperature of 62 degrees C.

Spatial solitons in liquid-crystal light valves

Liquid-crystal light valves can control the orientation of a nematic layer under the independent or combined action of applied voltage and impinging light intensity; hence, they offer a unique environment for the propagation of spatial optical solitons or nematicons. We demonstrate nematicon excitation, propagation, and steering in photoconductive light valves.

Readdressable Interconnects With Spatial Soliton Waveguides in Liquid Crystal Light Valves

We excite spatial solitons by reorientational nonlinearity of the nematic liquid crystals, using a photoconductive light valve to implement an external light-driven control of their trajectories. Control spots provide deviations of the solitons and allow implementing various routing operations. We demonstrate 2-bit (4-output) and 3-bit (8-output) spatial demultiplexers and a continuously adjustable X/Y power-dependent junction.

Bouncing localized structures in a liquid-crystal light-valve experiment.

In a liquid crystal light-valve experiment, we report solitary localized structures appearing outside the bistability range and displaying a behavior of single independent cells. The transition from an extended pattern to solitary states is characterized both experimentally and numerically.