Marek Wojciech Sierakowski

Self Focusing in Liquid Crystalline Waveguides

Abstract Nonlinear self-focusing of the laser beam in waveguide with nematic homeotropically aligned liquid crystalline layer is analysed theoretically and observed experimentally. The nonlinearity is caused by the reorientational effect and the stable self-trapped beams are created by the spatially periodic reorientation in the liquid crystalline layer.

Depolarization of partially coherent light in liquid crystals

In the paper we present results of analysis of partially coherent light depolarization in two types of liquid crystals possessing linear birefringence controlled by temperature and external electric field changes. Some experimental results of degree of polarization measurements for different light sources as a superluminescent diode and a laser diode are also presented.

Spatial Solitons in Twisted Nematic Layer

In this work we investigate light beam propagation in twisted nematic liquid crystalline film. Due to the optical reorientational nonlinearity light beam is self-focusing and finally the spatial solitary wave is created. With increasing the nonlinear effect the direction of light beam propagation is also changing. The samples were filled with 6CHBT nematic liquid crystal and the propagation of light beam at the distance of few millimeters was measured. Nonlinear self-focusing was obtained for a light power of few tenths of milliwats.

Light beam propagation in twisted nematics nonlinear waveguides

In the paper, the light beam propagation in twisted nematic liquid crystalline waveguides is analyzed theoretically. It is shown that optical reorientational nonlinearity in analyzed waveguides is large enough to observe spatial solitons formation with milliwatts of light power. The reorientational nonlinearity induces self-focusing and changes the direction of propagation of the light beam.

Polarimetric optical fibers with elliptical liquid-crystal core

We present experimental data on polarization properties of the light propagating in an anisotropic elliptical fiber with a liquid-crystal core in view of potential applications for use in polarimetric fiber-optic sensors.

Liquid Crystals and Polymer-Based Photonic Crystal Fibers

Experimental results of polymer photonic liquid crystal fibers based on commercially available (Kiriama) PMMA and cyclo-olefin polymer (Zeonex 480R) microstructured polymer fibers infiltrated with nematic liquid crystals (2CHBT/8CHBT and PCB) are presented and thermally-tuned photonic band-gap propagation mechanism is observed. These preliminary results suggest, that polymers binding to liquid crystals much easier than silica, can offer new opportunities while using polymer-based photonic crystal fibers.

Ionic Interface-effects in Electro-optical LC-cells

The work discusses ionic electrode processes in LC-cells driven by voltage. Ions in LC-material are generated by dissociation of residual impurities or (dye) additives, but by ageing of LC-material as well. Therefore even in carefully purified electro-optical cells temporal decomposition of the base material causes slow, but permanent increase of ion concentration. It is apparently manifesting in non-linear electrical response of LC-cell in the case of quick switching by pulse driving. Every change of voltage on cell electrodes induces re-charging process and causes flow of the space-charge limited current across LC-layer. Existence of the ions influences electro-optical performance of LC-cell. The ionic flow changes field distribution in LC-layer and can temporary distort molecular ordering. Ionic processes may superimpose an undesired intrusion on optical switching response of LC-cell and may result either in faster or in slower switching, depending on driving source parameters. In this paper we propose a simple model of ionic processes to explain the mechanism of non-linear ionic polarisation. Observed voltage - polarisation characteristics, space-charge current flow and an anomalous electro-optical behaviour of LC-cell can be explained by the model assumed. Concentration of the considered ions, their mobility, and activation energy is also evaluated.

Application of Optical Nonlinearity in Liquid Crystals to Optical Logic

Abstract New configurations of nonlinear liquid crystalline cells utilising an intensity-dependent scattering of light at liquid crystal/glass plate interface are presented. This kind of devices, based on a scattering-mode light modulation, require relatively low light power. Assistance of an additional electric field results in a more stable and a faster device performance.

A novel liquid crystal light modulator

Abstract We present a conception of two optical modulators. One of these, which we have called the scattering liquid crystal cell seems to be promising with a view to possible applications. We assumed that the modulator could be used in optical logic as a gate element, but other applications in optoelectronics would appear also to be possible. Some preliminary results of an experimental examination of the modulators are also presented.

Photonic liquid crystal fibers: Towards highly tunable photonic devices

Photonic liquid crystal fibers are hybrids that combine inorganic host micro-structured glass substrates with organic guest nanostructured liquid crystals. This combination creates a novel class of nano- and microstructured photonic crystal fibers and simultaneously is responsible for a diversity of new and uncommon material and optical properties. Due to the highest level of tunability induced by external electrical, magnetic, optical or thermal physical fields the effective Photonic liquid crystal fibers technology can be used for highly tunable advanced photonic devices.