Cesare Umeton

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.

Realization of particular liquid crystal cells for propagation and characterization of optical spatial soliton

We report on the design, fabrication process and characterization of liquid crystal cells for investigation of optical spatial solitons. Controlling of the director orientation at the input interface, as well as in the bulk, allows to obtain configurations that can produce distinct optical phenomena in a light beam propagating in the cell. For a particular director configuration, it is possible to produce two waves inside the nematic liquid crystal cell: the extraordinary and the ordinary one. With a different director configuration, the extraordinary wave only is obtained, which propagates inside the cell at an angle of more than 7 degrees with respect to the impinging wave vector direction. Under this peculiar configuration and by applying an external voltage, it is possible to have a good control of the propagation direction of the optical spatial soliton.

Gold nanoparticles embedded in flexible materials: new frontiers in Plasmonics

Fabrication of samples showing plasmonic properties is fundamental for the realization of devices that can exhibit peculiar electromagnetic properties. Here we illustrate results of experiments performed on systems with Au nanoparticles embedded in flexible substrates.

TRANSVERSE DYNAMICS OF ANISOTROPIC NEMATICONS

We investigate the role of anisotropy in the transverse dynamics of spatial solitons in nematic liquid crystals, owing to the interplay between walk-off, bias-induced index profile and self-confinement.

Walking anisotropic spatial solitons and their steering in nematic liquid crystals

A novel nematic liquid crystal cell allows the excitation of anisotropic spatial solitons and their angular steering, acting on walk-off thru the applied bias. The input interface enables polarization-healing soliton generation and spatial routing.