POLICRYPS composite structures: realization, characterization and exploitation for electro-optical and all-optical applications

The acronym POLICRYPS indicates a nano/micro composite structure made of films of well aligned nematic liquid crystal (NLC) alternated to slices of almost pure polymer. Structures are fabricated by curing a homogeneous mixture of mesogenic material, monomer and a curing agent with UV radiation, under suitable physical and geometrical conditions. In particular, geometrical conditions determine (in the range 0.2 ÷ 15 μ m) the spatial periodicity of the realized sample, which can be utilized for transmitting, diffracting or reflecting an impinging light beam, with negligible scattering losses. The 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/μ m or, in some cases, by irradiating the sample with a light beam of suitable wavelength. This electrical/optical tuneability is responsible for a series of distinctive characteristics of the optical effects produced by the structure, and determines the range of possible applications. In fact, in different geometries, the POLICRYPS can be exploited as a switchable holographic grating, a switchable optical phase modulator, a switchable beam splitter, a tuneable Bragg filter or it can be exploited as an electro-optical edge filter in an optical interrogation system.