The aim of this work is to create the regions of different effective refractive index in typical liquid crystal cell thanks to the polymer-stabilization. For this purpose typical liquid crystalline material, namely E7, has been combined with a small amount of the mixture of RM257 monomer and UV-sensitive activator, with percentage weight less than 10%. Thanks to the photo-polymerization process it is possible to obtain polymer-stabilized molecular orientation inside LC cell. In particular, periodic changes in spatial distribution of effective refractive index in LC layer have been achieved thanks to selective irradiation with UV light. Determination of suitable dose of both the monomer and UV-activator to be added to LC material, as well as of irradiation intensity and time, is essential and highly required to provide repeatable and good-quality periodic waveguiding structures. Eventually, functionality of the liquid crystal cells with distinguished regions of different molecular orientation, and in particular with combination of the planar and homeotropic alignment, has been experimentally tested by launching the near-infrared light beams of orthogonal linear polarizations. Thanks to the molecular reorientation induced by external electric field and/or by electromagnetic wave, it is additionally possible to control character of light propagation by electric bias and optical power, respectively. Proposed polymer-stabilized periodic waveguiding structures in liquid crystalline materials may find potential applications as functional elements and devices for LC-based integrated optics.
Fundamental properties of pure silica microstructured fibres (MSFs) can be determined by their geometrical crosssection design. Investigation of nonlinear effects was widely evaluated in diverse types of MSFs with exactly defined dispersive properties. Proper design of Zero Dispersion Wavelength (ZDW) strongly influences generation of nonlinear processes resulting especially in supercontinuum generation (SC). ZDW shift to short wavelengths together with high nonlinearity (small effective mode area) can be obtained by dramatic decrease of microstructured fibre pitch and increase of air-filling ratio. Fibre geometry must be properly scaled preserving technological tolerances to obtain precisely defined position of ZDW near visible range. Additionally, higher air-filling ratio results in multimode guiding regime. Therefore, in the paper we present studies of novel type of fibre geometry with ZDW near visible range together with endlessly single mode propagation regime. Chromatic dispersion measurements and ZDW analysis are performed with use of interferometric method. Presented MSFs series (the same structure type, but different ZDW position) is manufactured by stack and draw method. Proposed MSFs geometry enables fabrication of desired chromatic dispersion characteristic while respecting all technological tolerances, which is very difficult in case of manufacturing typical photonic crystal fibres for supercontinuum generated with 780 nm wavelength pulses from titanium-sapphire laser. Additionally, proposed endlessly single mode operation provides high quality white light output beam, simultaneously with stable and flat SC source. Paper also reports on the SC generation with pumping in the anomalous and normal side of chromatic dispersion with femtoseconds and picoseconds pulses.
In this work we present the 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 few millimeters and the nonlinear selffocusing
was observed for a light power of order of few tenths of milliwats. The experimental results are in a good
agreement with theoretical predictions.
We investigate linear and nonlinear light propagation in the multicore fiber. Such a structure, with a periodic modulation of refractive index in one-dimension, allows for the study of discrete optical phenomena. Light intensity distribution in such structure changes with propagation length and also depends on the input beam position. Additionaly, in nonlinear regime it changes with the increase of light power. We present both theoretical and experimental results on the nonlinear light propagation in the silica multicore fiber, where the near infrared wavelength from femtosecund laser Ti:Saphire propagates in a distance of a few centimeters.
In this work nonlinear light propagation in a photonic crystal fiber (PCF) infiltrated with a nematic liquid crystal
(NLC) is presented. Such a photonic structure, called the photonic liquid crystal fiber (PLCF), combines the passive PCF
and the active NLC guest mixture. The analyzed configuration with a periodic modulation of spatial refractive index
distribution corresponds to the matrix of waveguides. This kind of structure can be controlled by optical power and
additionally by temperature and it allows for studying variety of discrete optical phenomena. For properly chosen
parameters of the analyzed fiber, discrete diffraction in the linear case and generation of the discrete spatial soliton in
nonlinear regime can be obtained. In this paper a possibility of the transverse light localization and delocalization due to
both focusing and defocusing Kerr-type nonlinearity was analyzed. In the case of the positive nonlinearity the refractive
index increases as a function of light intensity in such a way that the stronger guiding of the light within NLC cores is
obtained. Light modifies the refractive index distribution inducing a defect in the periodic structure. That can lead to the
situation in which light becomes self-localized and its diffractive broadening is eliminated. Eventually the discrete
soliton can be created. In the case of negative nonlinearity, the difference between NLC waveguides and glass refractive
indices decreases and the beam guidance becomes weaker for higher light intensities. In such a case the generation of the
bright soliton is possible only in the regime of negative discrete diffraction. However, in the case of defocusing
nonlinearity a decrease of refractive index with the optical power can lead to the bandgap shifting. The incident beam
with a frequency initially within a bandgap is then turned outside the bandgap resulting in changing of the propagation
mechanism to the modified total internal reflection.
In this paper the tunable properties of the photonic liquid crystal fibers are analyzed. Both numerical and experimental
results on the linear light propagation in the photonic crystal fiber filled with the glycerin-water solution and with
6CHBT nematics are presented. Investigated fiber called as photonic liquid crystal fiber combines the passive photonic
crystal fiber host structure and an active nematic liquid crystal material. Such a photonic structure, with a periodic
modulation of refractive index, which could be additionally controlled by the temperature and by the optical power,
allows for the study of discrete optical phenomena.