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Light propagation in periodic photonic structures formed by photo-orientation and photo-polymerization of nematic liquid crystals

Rutkowska K. A., Chychłowski M., Kwaśny M., Ostromęcka I., Piłka J., Laudyn U. A.

Opto-Electronics Review

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2017

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Vol. 25, No. 2

118--126

EN

Propagation of linearly polarized light beams in a nematic liquid crystal cell with distinguished regions of different molecular orientation has been analyzed. Specifically, combination of the planar/homogenic and homeotropic alignment, forming thus spatially limited regions characterized by a different LC molecular orientation, has been tested, as achieved by means of the photo-orientation and photo-polymerization processes, independently. An influence of molecular orientation on the light beam propagation has been checked for different directions of the linear polarization. Thanks to the molecular reorientation induced by the low frequency external electric field and also to the reorientational nonlinearity taking place in NLCs, propagation direction of the light beam can be additionally controlled by the electric bias and/or optical power, respectively. Proposed structural solutions and techniques, related to the photo-orientation and photo-polymerization processes described in this communication, give rise to the novel LC geometries and structures. The latter act as promising candidates for new practical photonic applications as they are expected to be of a particular importance for integrated optic elements and devices.

2

Wybrane optyczne zjawiska nieliniowe w mikrostrukturach fotonicznych i ośrodkach magnetooptycznych

Rutkowska K. A.

Prace Naukowe Politechniki Warszawskiej. Fizyka

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2015

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z. 58

3--181

PL

W pracy przedstawiono opis wybranych zjawisk nieliniowych drugiego i trzeciego rzędu, w których wykorzystywana jest zarówno specyfika struktur falowodowych wykonanych z różnych materiałów, jak również indukowana zewnętrznym polem magnetycznym dwójłomność optyczna pozwalająca na uzyskanie quasi-stacjonarnych rozwiązań w objętościowym ośrodku kerrowskim. Niniejsze opracowanie zawiera opis teoretyczny rozpatrywanych zagadnień, a także wyniki badań eksperymentalnych. Przeanalizowane w pracy procesy i zjawiska typowe dla optyki nieliniowej, takie jak przykładowo generacja drugiej harmonicznej, samoogniskowanie światła, czy generacja solitonów przestrzennych w ośrodkach kerrowskich, zostały opisane na podstawie oryginalnych badań własnych autorki. Wskazuje ona przy tym, że odmienne mechanizmy nieliniowości występujące w różnych badanych przez nią ośrodkach materialnych wpływają na przebieg analizowanych zjawisk nieliniowych i umożliwiają ich potencjalne zastosowania przy praktycznym konstruowaniu układów i urządzeń fotonicznych. W monografii opisane zostały zarówno różnorodne metody analityczne i numeryczne stosowane przy analizie zagadnień związanych z propagacją światła i projektowaniu struktur fotonicznych, jak również metody pomiarowe i techniki eksperymentalne stosowane przy charakteryzacji i optymalizacji struktur i układów optycznych wykorzystywanych w optyce nieliniowej.

EN

In this work selected second- and third-order optical nonlinear phenomena are described, in which unique properties of waveguiding structures made of various materials as well as magnetically induced optical birefringence allowing for quasi-stationary solutions in bulk Kerr-type media are utilized. Presented studies include both theoretical description of the analyzed subjects, as well as experimental results. Based on original research achievements of the author, selected nonlinear optical processes and phenomena, such as, for example, second harmonic generation, self-focusing and spatial solitons generation in Kerr-type media are considered. It is indicated that different mechanisms of nonlinearity occurring in various materials under investigations influence nonlinear processes and thus allow for potential application of prospective photonic devices and systems. This treatise describes various analytical an numerical methods used for analyses of light propagation in selected photonic structures as well as measurement methods and experimental techniques applied for characterization and optimization of the proposed structures and systems to be used in nonlinear optics.

3

Light propagation mechanism switching in a liquid crystal infiltrated microstructured polymer optical fibre

Rutkowska K. A., Milenko K., Chojnowska O., Dąbrowski R., Woliński T. R.

Opto-Electronics Review

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2015

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Vol. 23, No. 4

252-258

EN

In this work studies on propagation properties of a microstructured polymer optical fibre infiltrated with a nematic liquid crystal are presented. Specifically, the influence of an infiltration method on the LC molecular alignment inside fibre air-channels and, thus, on light guidance is discussed. Switching between propagation mechanisms, namely the transition from modified total internal reflection (mTIR) to the photonic bandgap effect obtained by varying external temperature is also demonstrated.

4

Tunability of discrete diffraction in photonic liquid crystal fibres

Rutkowska K. A., Laudyn U. A., Jung P. S.

Opto-Electronics Review

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2014

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Vol. 22, No. 4

207-217

EN

In this paper theoretical and experimental results regarding discrete light propagation in photonic liquid crystal fibres (PLCFs) are presented. Particular interest is focused on tunability of the beam guidance obtained due to the variation in either external temperature or optical power (with assumption of thermal nonlinearity taking place in liquid crystals). Highly tunable (discrete) diffraction and thermal self-(de)focusing are studied and tested in experimental conditions. Specifically, spatial light localization and/or delocalization due to the change in tuning parameters are demonstrated, with possibility of discrete spatial (gap) soliton propagation in particular conditions. Results of numerical simulations (performed for the Gaussian beams of different widths and wavelengths) have been compared to those from experimental tests performed in the PLCFs of interest. Owning to the limit of experimental means, direct qualitative comparison was not quite accessible. Nevertheless, a qualitative agreement between theoretical and experimental data (obtained in analogous conditions) has been achieved, suggesting a compact and widely-accessible platform for the study of tunable linear (and nonlinear) discrete light propagation in two-dimensional systems. Proposed photonic structures are of a great potential for all-optical beam shaping and switching.

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Light induced angular steering via Floquet-Bloch band-tunnelling in one-dimensional liquid photonic lattices

Fratalocchi A., Rutkowska K. A., Karpierz M. A., Assanto G.

Opto-Electronics Review

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2007

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Vol. 15, No. 4

210-214

EN

We investigate all-optical Zener tunnelling in electro-optically tunable arrays of identical channel waveguides in undoped nematic liquid crystals. By all-optically inducing a refractive acceleration, we demonstrate a novel technique for band-to-band tunnelling, as well as a novel approach to light controlled steering and readdressing.