Observation
of out-coupling of a nematicon
J. BEECKMAN, K. NEYTS, X. HUTSEBAUT, and M. HAELTERMAN
In this work we present the observation of spatial optical solitons in liquid crystal cells by recording the diffraction pattern of the out-coupled beam on a distant screen. Simultaneously, the light propagation is observed via scattering measurements. The most important observation is displacement of the beam on the screen due to the transverse undulation inside the cell. This undulation is caused by the anisotropic walk-off of the beam. The displacement is in good agreement with the values of the undulation earlier reported.
Keywords: liquid crystals, optical spatial solitons, lateral light propagation.
Design
and simulation of single-electrode liquid crystal phased arrays
B. BELLINI, M.A. GEDAY, N.
BENNIS, A. SPADLO, X. QUINTANA, J.M. OTON and R. DABROWSKI
Liquid crystal (LC) phased arrays and gratings have been employed in optical switching and routing [1]. These diffractive optic elements are of great interest because they can be scaled up to a large number of elements and their optical properties can be electrically addressed with a low driving voltage. LC phase gratings have been achieved either by periodic addressing of pixels or by using periodically-modified structures. The latter approach leads to less reconfigurable devices but the addressing is simpler.
In this paper we focus on optical phased arrays where the phase is varied either continuously or discretely and where the periodicity is induced by electrode configuration. We first describe a possible structure based on a conductive silicon wafer. We argue that this structure can induce either continuously or discretely varying arrays while applying single voltage to the array. In the second part we simulate the behaviour of such arrays. We base the simulation on a LC synthesized at the Military University of Technology, this high-birefringence nematic LC shows in a 4-μm thick cell a linear phase shift range of more than 3600 between 1.2 V and 1.8 V. We calculate the distribution of the LC molecule director and assess the performance of the array with respect to the applied voltage. Finally, the relevance of such technology for switchable phased arrays is discussed.
Keywords: liquid crystals, phased arrays, silicon.
Nonlinear
optical properties of composites based on conductive metal-alkanoate
S. BUGAYCHUK, G. KLIMUSHEVA, Y.
GARBOVSKIY, T. MIRNAYA and A. ISCHENKO
The dynamic holography in new composite materials based on a novel class of metal-alkanoate ionic liquid crystals (ILCs) is studied experimentally and theoretically. The composites are formed as a dielectric dye film covered by lyotropic metal-alkanoate ILC and ionic smectic glasses with doped dye molecules. The dynamic gratings are created by nanosecond pulses of double frequency Nd:YAP laser, the recording demonstrates fast erasure time of residual thermal gratings. The nonlinear optical properties are determined by the resonance nonlinearity in photosensitive centres of ILC. Note, that permanent relief gratings will be formed on a dielectric dye film only as well as in composite cells either with nematic LC or with polymers under action of pulsed laser radiation. Lyotropic ILC layer applied over the dye film provides the dynamic regime of grating recording in composite cells. We found a secondary thermal grating is much smaller, the conductive ILC matrix provides effective heat dissipation and erasure of this thermal grating. A theory of Raman-Nath self-diffraction holography on thin films followed from the wave equation and the nonlinear mechanism of absorption saturation is developed to explain experimental results.
Keywords: ionic liquid crystals, dynamic holographic recording, composites.
Low
threshold voltage asymmetric antiferroelectric liquid crystal cells
N. BENNIS, A. SPADLO, R. DABROWSKI, E.
MARTINELLI, G. GALLI, X. QUINTANA, J.M. OTON and M.A. GEDAY
Asymmetric antiferroelectric liquid crystal displays (AAFLCD) are attractive since they show a very well defined off state and fast switching time. Moreover, they can be driven by a simple biasless DC compensated waveform. The electrooptical response of an AAFLCD allows for new addressing modes, including quasi-static intermediate greyscales maintained without applying a field and passively addressed multiplexed high-frequency displays and spatial light modulators. A new kind of asymmetric cells have been obtained by using fluorinated block copolymer (FBC) alignment, which enhances surface segregation and provides a low energy surface. In this work we combine FBC alignment with antiferroelectric liquid crystal mixtures containing strongly electronegative fluorinated components. Threshold voltages for the antiferroelectric-ferroelectric phase transition as low as 3 volts are observed. We report the time evolution of the shift of the electro-optical response.
Keywords: antiferroelectric liquid crystals, multistable analogue retardation, alignment layer.
Linear and
nonlinear properties of photonic crystal fibers filled with nematic
K.A. BRZDAKIEWICZ, U.A.
LAUDYN, M.A. KARPIERZ, T.R. WOLINSKI, and J. WOJCIK
We investigate linear and nonlinear light propagation in the photonic crystal fibers infiltrated with nematic liquid crystals. Such a photonic structure, with 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. Our theoretical investigations, carried out with the near infrared wavelength of 830 nm, for both focusing and defocusing Kerr-type nonlinearity, show the possibility of the transverse light localization, which can result in the discrete soliton generation. In addition, we present the preliminary experimental results on the linear light propagation in the photonic crystal fiber with the glycerin-water solution and 6CHBT nematics, as the guest materials.
Keywords: photonic crystal fibers, optical nonlinearity in liquid crystals, solitons, discrete diffraction.
Formation
and dynamics of easy orientation axis in magnetic field on
O. BULUY, Y. REZNIKOV, K. SLYUSARENKO, M.
NOBILI and V. RESHETNYAK
We describe the experiments on a magnetically-induced drift of the easy axis on a soft surface of photoaligning material fluoro-polyvinyl-cinnamate. We found unexpected partial relaxation of the drift of the easy axis after switching the magnetic field off. This relaxation cannot be explained in a framework of the existing models and requires additional assumptions about the drift process. We propose a model that explains the experimental data suggesting elastic-like behaviour of the polymer fragments during the drift of the easy axis.
Keywords: liquid crystal, easy axis, gliding, drift of easy axis, photoalignment.
Tunable
topographical cellulose matrices for electro-optical liquid crystal
I. COSTA, P.L. ALMEIDA, D.
FILIP, J.L. FIGUEIRINHAS and M.H. GODINHO
In this work we have used acetoxypropylcellulose (APC) to produce free standing solid films (~60 μm) that were used for assembling electro-optical devices. Thin films were obtained from concentrated lyotropic solutions of cellulose derivatives. Induced by the cast and shearing preparation conditions wrinkles and band textures can be observed in their free-surface plane. In order to eliminate and control these textures we used a process similar to that introduced in literature [1] which consists of storing the films in the same solvent-vapour atmosphere as the solution system. Lyotropic APC liquid crystalline solutions in dymethylacetamide (DMA) with crosslinker were prepared, thin films were obtained by using a shear/casting technique and stored in the solvent-vapour atmosphere until a planar structure was achieved. The dried crosslinked films were analyzed by optical polarised microscopy (POM) and scanning electron microscopy (SEM). The films with different topographies were used to produce optical cells composed by the cellulose derivative film covered on both free surfaces by a layer of the nematic liquid crystal E7 and placed between two transparent conducting substrates. The electro-optical properties of these cells were obtained.
Keywords: acetoxypropylcellulose, liquid crystals, PDLC, electro-optical properties.
Depolarization
of partially coherent light in liquid crystals
A.W. DOMANSKI, D. BUDASZEWSKI, M. SIERAKOWSKI and T.R. WOLINSKI
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.
Keywords: depolarization of light, liquid crystals, coherency of light.
Reconfigurable
optical multiplexer based on liquid crystals for polymer
P.C. LALLANA, C. VAZQUEZ, J.M.S.
PENA and R. VERGAZ
In this work, different novel 3×1 multiplexer structures for being used in polymer optical fiber networks are proposed. Designs are compact, scalable, and of low consumption, capable of operating in a large wavelength range simultaneously 660, 850, and 1300 nm, due to the use of nematic liquid crystal cells. Light that comes from each input port is handled independently and eight operation modes are possible. Control electronics has been made using a programmable integrated circuit. Electronic system makes available the managing of the optical stage using a computer. An additional four optical sensors have been included for allowing the optical status checking.
Finally, a polarization independent multiplexer has been implemented and tested. Insertion losses less than 4 dB and isolation better than 23 dB have been measured. In addition, 30-ms and 15-ms setup and rise times have been obtained. The proposed multiplexer can be used in any polymer optical fiber network, even in perfluorinated graded index one, and it can be specially useful in optical sensor networks, or in coarse wavelength division multiplexing networks.
Keywords: multiplexer, liquid crystals, polymer optical fiber, coarse wavelength division multiplexing.
Electrooptic
study of antiferroelectric mixtures for display application
A. MIKULKO, M. MARZEC, S. WROBEL and R. DABROWSKI
The aim of this paper is to study the influence of electric field on alignment of para-, ferro- and antiferroelectric phases in the vicinity of SmA* – SmC* or SmC* – SmC*A phase transitions as to obtain mono-domain cells. Four mixtures studied (W-193B, W-193B-1, W-201, W-204D) show the SmC*A phase in a wide room temperature range. Measurements of the spontaneous polarization versus temperature by using reversal current method give an answer to the question, what kind of the transitions take place between para-, ferro- or antiferroelectric phases using the Landau mean field theory. Optimal electrooptic parameters for different compositions of the mixtures such as tilt angle, spontaneous polarization and saturation voltage have been measured to compare parameters of the mixtures studied.
Keywords: antiferroelectric mixtures, tilt angle, spontaneous polarization.
General
properties of lasing effect in chiral liquid crystals
S.P. PALTO, N.M. SHTYKOV, B.A.
UMANSKY, M.I. BARNIK and L.M. BLINOV
Numerical simulations and experimental studies of the lasing effect in chiral liquid crystals are presented. It is shown that ring-like light emission, which is often observed experimentally, is a true lasing effect. Lasing condition and different modes in thin liquid crystal layers are discussed.
Keywords: liquid crystals, optics, lasing.
Photonic
liquid crystal fibers – a new challenge for fiber optics and liquid
T.R. WOLINSKI, S. ERTMAN, P.
LESIAK, A.W. DOMANSKI, A. CZAPLA, R. DABROWSKI, E. NOWINOWSKI-KRUSZELNICKI, and J. WOJCIK
The paper reviews and discusses the latest developments in the field of the photonic liquid crystal fibers that have occurred for the last three years in view of new challenges for both fiber optics and liquid crystal photonics. In particular, we present the latest experimental results on electrically induced birefringence in photonic liquid crystal fibers and discuss possibilities and directions of future developments.
Keywords: liquid crystals, photonic crystal fibers, induced birefringence.
Optical
data storage in LC cells
M. SUTKOWSKI, T. GRUDNIEWSKI, R.
ZMIJAN, J. PARKA and E. NOWINOWSKI-KRUSZELNICKI
Liquid crystal devices as a medium for holograms storage have been investigated. Long term memory effects in LC cells have been observed. Experiments proved that certain combination of insulating alignment layers has a major influence on the long term memory effect. Optimal liquid crystal cell construction allows us to achieve sufficient diffraction efficiency to record holographic patterns and to develop a re-writable holographic medium. The configuration of PVK and polyimide layers in LC cell construction with specific LC mixture was tested. The method of permanent and re-writable recording of optical data (holographic pattern) onto LC cells was achieved. However, the method of erasing recorded data was realized but mechanisms of this phenomenon are not clearly understood yet.
Keywords: photorefractive liquid crystals, holography, optical data storage.
Tunable
properties of light propagation in photonic liquid crystal fibers
K. SZANIAWSKA, T. NASILOWSKI, T.R. WOLINSKI and H.
THIENPONT
Tunable properties of light propagation in photonic crystal fibers filled with liquid crystals, called photonic liquid crystal fibers (PLCFs) are presented. The propagation properties of PLCFs strongly depend on contrast between refractive indices of the solid core (pure silica glass) and liquid crystals (LCs) filing the holes of the fiber. Due to relatively strong thermo-optical effect, we can change the refractive index of the LC by changing its temperature. Numerical analysis of light propagation in PLCF, based on two simulation methods, such as finite difference (FD) and multipole method (MM) is presented. The numerical results obtained are in good agreement with our earlier experimental results presented elsewhere [1].
Keywords: liquid crystals, photonic band gap, optical fibers, photonic crystal fibers.