Characterization of an active control system for holographic setup stabilization

Abstract

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.

Soft Periodic Microstructures Containing Liquid Crystals

“…The curing process is carried out at a 100 nm precision level, by utilizing an optical holographic setup that enables the spatial periodicity of the structure to be easily varied from the almost nanometric to the micrometric range. 23,24 The POM view of a POLICRYPS structure with a periodicity of Λ= 5 μm, reported in Figure 1a, reflects the almost complete phase separation that is usually achieved in this kind of systems and evidences the absence of LC droplets, whose presence could yield some scattering of the impinging light and some depolarization of the transmitted/diffracted one. Figure 1b is a side view of the POLICRYPS structure acquired by means of an environmental scanning electron microscope (ESEM) after removing the top cover glass.…”

Optical Properties of Electrically Tunable Two-Dimensional Photonic Lattice Structures Formed in a Holographic Polymer-Dispersed Liquid Crystal Film: Analysis and Experiment

“…After 20-minutes holographic exposure the HPDLC film was post-cured with an ultraviolet LED light source operating at a wavelength of 365 nm for 30 minutes to ensure that remaining monomer, if any, was consumed completely. Although we employed a conventional three-beam holographic setup [56,57] without any particular phase stabilization control [58,59], any nonlinear effect such as wave mixing between interfering beams during curing [60] would not play a role in our fabrication process. This is so because good agreement is seen between the morphology of our fabricated PhC structures and the calculated ones as will be seen in Subsection 4.1.…”

Full Optical Control of Holographic Gratings Realized in Composite Materials Containing Photosensitive Liquid Crystals

“…POLICRYPS fabrication has been realized by means of the UV holographic setup described in details elsewhere [6], implemented with a new technique for high stability curing [8,9]. For our experiments, a POLICRYPS grating with a periodicity K ¼ 1.6 mm and thickness d ¼ 11.4 mm has been realized, following the procedure of Ref.…”