A new polymeric - liquid crystAlline composite templAte for opticAl, electro-opticAl And All-opticAl ApplicAtions cesAre pAolo umeton

1 The POLICRYPS structure In the last decades, great attention has been devoted to the realization of switchable holographic structures in liquid crystalline composite materials [1]. In particular, it has been shown that diffraction gratings based on Holographic Polymer Dispersed Liquid Crystals (HPDLC), that means droplets of Nematic Liquid Crystal (NLC) dispersed in a polymer matrix (see insert 1), are low cost and can exhibit good performances [2]. However, applicationoriented utilization of these devices is very often limited by their strong scattering of light, due to the circumstance that the average size of NLC droplets is, in general, comparable to the wavelength of the impinging light. For this reason, it has been recently designed, fabricated, patented and deeply investigated a new kind of holographic grating called POLICRYPS (acronym of POlymer LIquid CRYstal Polymer Slices), which is made of slices of almost pure polymer alternated to films of uniformly aligned NLC. These structures present a sharp morphology of high optical quality and, if used as diffraction gratings, they can exhibit values of the diffraction efficiency as high as 98%. The acronym POLICRYPS indicates a micro-composite structure made of slices of almost pure polymer alternated to films of well aligned Nematic Liquid Crystal (NLC), with a spatial periodicity that can be settled in the range 0.2–15 mm. It can be utilized for transmitting, diffracting or reflecting an impinging light beam with negligible scattering losses, while the optical effects of a spatial modulation of the refractive index (from polymer to NLC) can be switched on and off both by applying an electric field of few V/mm or, in some cases, by irradiating the sample with a light beam of suitable wavelength. In different geometries, the POLICRYPS can be exploited as a switchable diffraction grating, a switchable optical phase modulator and a switchable beam splitter.