We report on the realization and characterization of an active control system of the optical holographic setup used for fabrication of holographic gratings in liquid-crystalline composite materials. The system exploits a reference diffraction grating and a piezomirror in closed-loop feedback. The piezoelectric mirror exhibits a hysteresis that depends not only on the applied voltage, but also on the history of the mirror motion. In an open-loop configuration, the hysteresis can be reduced by adjusting the delay time between the application of two different control voltage values; in a closed-loop operation, it is possible to eliminate the residual hysteresis. By testing the system in different conditions, it has been shown that residual fluctuations are comparable to the resolution of the piezomirror operation.

We report our recent efforts on the fabrication and characterization of light responsive devices realized in soft composite materials. Periodic microstructures obtained by means of a photolithographic technique and a chemical etching process have been used to micro confine a light responsive liquid crystal stabilized through a self-organization processes.The high quality, light responsive, periodic microstructures have been exploited for realizing different all-optical, fast and low power applications. An overview of the realized photonic devices is presented.

No abstract

We present the results of realization and study of a light beam splitting effect based on a full-optically controlled holographic diffraction grating. The high quality, light responsive, periodic structure, which is exploited as tunable beam splitter, is monitored by combining its zero and first diffracted orders in a Mach-Zehnder geometry interferometer. The interference pattern exhibits a dependence of the fringe visibility on the external optical pump power utilized to drive the splitting effect. The visibility, characterized by means of a standard pump-probe optical setup, reveals a strong dependence on the polarization of the probe radiation and on its incident angle as well. The effect is reversible and repeatable, and shows a continuously adjustable fringe visibility in the range 0.94-0.2, with response times in the millisecond range.

No abstract