Miroslaw A. Karpierz

Nematicons: self-localised beams in nematic liquid crystals

We review the impressive progress on light self-localisation into spatial optical solitons in nematic liquid crystals. We summarise the basic physics and models, outlining the main properties of nematicons and providing an overview of the most significant experimental achievements in undoped, planar, twisted and chiral nematic liquid crystals.

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.

Influence of different peripheral substituents on the nonlinear optical properties of cobalt phthalocyanine core

In this article, we show how the substituting different peripheral substituents around the cobalt phthalocyanine core correlate with nonlinear optical properties. We present the results on nonlinear optical properties of solution of cobalt phthalocyanine (CoPc), cobalt phthalocyanine with DNA-CTMA surfactant complex (CoPc-DNA-CTMA), and cobalt phthalocyanine with liquid crystal (CoPc-LC) measured by degenerate four-wave mixing (DFWM) method at the 532 nm wavelength region. We found that the values of third-order nonlinear optical susceptibility (χ⟨3⟩) of CoPc-LC and CoPc-DNA-CTMA increase in comparison with the value of the third-order nonlinear optical susceptibilities of CoPc. We supposed that this is caused by increase of the charge-transfer effects and of the dipole moments of the molecule with the increase of the chain length.

Nematicons in chiral nematic liquid crystals

We report on the experimental studies of the existence of spatial solitons called nematicons in chiral nematic liquid crystal cells. The low absorption allows us to observe soliton propagation at a distance of over a few millimeters in range. The results of our experiment also show that it is possible to create independent nematicons in different layers formed by a helical structure of the liquid crystals.

Coupled solitons in waveguides with cascaded second order nonlinearity

Abstract The propagation of two pulses in optical waveguides with second order nonlinearity is analyzed. Analytical solutions in the form of coupled solitons are presented and it is shown by utilizing the Beam Propagation Method that they are stable at long distances.

Coupled solitons in waveguides with second- and third-order nonlinearities

The analytical form of coupled temporal solitons in waveguides with second- and third-order nonlinearities is presented. The solutions are obtained for group-velocity dispersions of the same sign for both fundamental and second-harmonic frequencies. In particular, three types of coupled soliton are found: bright solitons, which can exist in materials with second- or third-order nonlinearities; semidark (twin-hole) solitons, which require materials with second-order nonlinearity; and gray coupled solitons existing only in materials with both nonvanishing nonlinearities.

Spatial solitons in chiral nematics

In this work we present for the first time experimental results of measurements of spatial solitons (nematicons) in chiral nematic liquid crystalline film. We measured the propagation of light beam at the distance of a few millimeters and the nonlinear self-focusing was observed for a light power of order of a few tenths of milliwats. Additional, in a waveguide induced by the nematicon, other low-power light beam (signal beam) with different wavelength was trapped. There were also observed the changes of the nematicon direction by changing the position across the nematics layer. The experimental results are in a good agreement with theoretical predictions.

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.

Modeling of molecular reorientation and beam propagation in chiral and non-chiral nematic liquid crystals

The exact molecular reorientation model for nematic liquid crystals taking into account all diagonal Frank elastic constants and using two angles to describe director orientation is presented. Solutions and simplified equations are shown for the most common planar and chiral configurations. Gaussian beam propagation simulated using fully vectorial Beam Propagation Method in nonlinear case is also provided. Detailed comparison between exact solutions and single Frank constant approximation is made. However, no significant differences between these two models were found neither in beam propagation nor in polarization distribution, some difficulties may occur in choosing single Frank constant especially when it comes to quantitative results. Presented results correspond to a propagation of a beam of the Gaussian or topologically similar shapes.

Nematicon–nematicon interactions in a medium with tunable nonlinearity and fixed nonlocality

We investigate the attractive interaction between spatial solitons in nematic liquid crystals with a tunable nonlinearity and a constant nonlocality. The experimental study, carried out by controlling the orientation of the optic axis via the electro-optic response, shows how the interactions depend on reorientation, in excellent agreement with a model accounting for the anisotropic nature of the dielectric.