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1
Content available remote Silicon oxides as alignment surfaces for vertically-aligned nematics in photonic devices
Oton E., López-Andrés S., Bennis N., Otón J. M., Geday M. A.
Opto-Electronics Review
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2014
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Vol. 22, No. 2
92-100
EN
A comparative study on alignment performance and microstructure of inorganic layers used for liquid crystal cell conditioning has been carried out. The study has focused on two specific materials, SiOx and SiO₂, deposited under different conditions. The purpose was to establish a relationship between layer microstructure and liquid crystal alignment. The surface morphology has been studied by FESEM and AFM. An analysis on liquid crystal alignment, pretilt angle, response time, contrast ratio and the conditions to develop backflow effect (significant rise time increase due to pure homeotropic alignment) on vertically-aligned nematic cells has been carried out. A technique to overcome the presence of backflow has been identified. The full comparative study of SiOx and SiO₂ layer properties and their influence over liquid crystal alignment and electrooptic response is presented.
2
Content available remote Security devices based on liquid crystals doped with a colour dye
Carrasco-Vela C., Quintana X., Otón E., Geday M. A., Otón J. M.
Opto-Electronics Review
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2011
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Vol. 19, No. 4
495-500
EN
Liquid crystal properties make them useful for the development of security devices in applications of authentication and detection of fakes. Induced orientation of liquid crystal molecules and birefringence are the two main properties used in security devices. Employing liquid crystal and dichroic colorants, we have developed devices that show, with the aid of a polarizer, multiple images on each side of the device. Rubbed polyimide is used as alignment layer on each substrate of the LC cell. By rubbing the polyimide in different directions in each substrate it is possible to create any kind of symbols, drawings or motifs with a greyscale; the more complex the created device is, the more difficult is to fake it. To identify the motifs it is necessary to use polarized light. Depending on whether the polarizer is located in front of the LC cell or behind it, different motifs from one or the other substrate are shown. The effect arises from the dopant colour dye added to the liquid crystal, the induced orientation and the twist structure. In practice, a grazing reflection on a dielectric surface is polarized enough to see the effect. Any LC flat panel display can obviously be used as backlight as well.
3
Content available remote Influence of a helical pitch on orthoconic antiferroelectric liquid crystals performance
Bennis N., Dąrowski R., Rejmer W., Spadło A., Quintana X., Otón J. M.
Opto-Electronics Review
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2011
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Vol. 19, No. 1
71-75
EN
Orthoconic antiferroelectric liquid crystals, whose half cone angle is 45°, are of interest in display technology because they are capable of providing greyscale in passively addressing waveform while exhibiting very good contrast. However, orthoconic antiferroelectrics having short pitch are difficult to be aligned, this makes surface stabilized alignment unfeasible. In this case, dynamic behaviour is usually poor, avoiding electronic addressing with standard electronics. In this work, we report the helical pitch measurements of OAFLC mixtures and we compare electrooptical performance of high and low pitch OAFLCs.
4
Content available remote Comparative electrooptic study of new orthoconic liquid crystals with fluorinated alkoxy terminal chains
Spadło A., Otón E., Dąbrowski R., Żurowska M., Otón J. M., Bennis N.
Opto-Electronics Review
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2010
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Vol. 18, No. 2
219-222
EN
Electrooptical properties of several new orthoconic antiferroelectric liquid crystal mixtures with partially fluorinated alkoxyalkoxy terminal chains have been investigated in order to select the best mixture for display applications. Electrooptical studies have been performed on these orthoconic materials aiming at evaluating their static and dynamic performance under passive multiplexing conditions. A number of parameters have been evaluated, static and dynamic contrast, driving scheme for passive multiplexing, rise and fall response times, dynamic range, and dynamic greyscale.
5
Content available remote PEDOT as an alignment layer and electrode in AFLC devices
Medialdea D. P., Bennis N., Cerrolaza B., Quintana X., Otón J. M., Arredondo B., Romero B., Geday M. A.
Opto-Electronics Review
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2009
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Vol. 17, No. 1
78-83
EN
PEDOT [Poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonate)] is a material typically used organic light emission displays (OLEDs) manufactured as a conductor, or rather, as a hole injector. In this paper, three different issues have been studied: the use of rubbed PEDOT as alignment layer, the resistivity of the applied PEDOT layers, i.e., its potential as a replacement of ITO electrodes, and the induction of asymmetry in the electro-optical response of liquid crystal cells by assembling the display with dissimilar coated aligning surfaces - PEDOT on one side and buffed nylon on the counter electrode.
6
Content available remote Nearly-analogue blazed phase grating using high birefringence liquid crystal
Bennis N., Geday M. A., Quintana X., Cerrolaza B., Medialdea D. P., Spadło A., Dąbrowski R., Otón J. M.
Opto-Electronics Review
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2009
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Vol. 17, No. 2
112-115
EN
Diffraction of liquid crystal gratings has been thoroughly studied for many applications such as diffraction optics, optical processing, and spectral analysis. In pure optical processing one varies the direction of propagation of light beam without any mechanical adjustment. In this work we propose a beam steering device using highly birefringent liquid crystal material. Using a highly birefringent material one can reduce the LC layer thickness needed to achieve 2 π of phase modulation and thus reduce the fringing effect caused by deformation of the electric field at the edge of the pixel. Here, we present 1.5-µm thick, high-resolution diffraction grating with non-detectable fringing.
7
Content available remote Effect of bias in ferroelectric-antiferroelectric relaxation
Geday M. A., Medialdea D. P., Cerrolaza B., Bennis N., Quintana X., Otón J. M.
Opto-Electronics Review
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2009
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Vol. 17, No. 2
140-143
EN
The ferroelectric-antiferroelectric transition in greyscale generation of antiferroelectric liquid crystal displays (AFLC) is a heterogeneous process. The process has been described as the growth of finger-like domains [1]. We have previously studied the ferroelectric-antiferroelectric phase transition, relaxation that follows the data pulse in surface stabilized asymmetric antiferroelectric liquid crystal displays using biasless video frequency waveforms [2]. This relaxation involves an intensity decay of the light transmitted by a pixel and depends on several parameters such as surface stabilization, rotational viscosity of the AFLC, magnitude of the data pulse, and bias voltage. The usual multiplexed driving of AFLC displays leads to long-term stabilisation of the grey levels induced by the data pulses within the selection time. However, depending on the bias level, alternative greyscale mechanisms may be obtained by allowing the grey levels to decay during the frametime. These greyscales may be advantageous in some instances since they improve the dynamic response of the AFLC device and reduce the reset time of the waveform. In this study we extend the previous work to include the effect of bias. We present the measured data, in terms of growth pattern and speed and present an extension of the previously model on order to explain the results.
8
Content available remote Temporal electrical response of chiral smectic liquid crystal displays with V/W-shaped electrooptical characteristic
Pena J. M. S., Pérez I., Urruchi J., Torres J. C., Otón J. M.
Opto-Electronics Review
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2008
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Vol. 16, No. 2
189-193
EN
Chiral smectic liquid crystal cells showing V-shaped electrooptical switching have been reported as one of the most promising technologies for high-end display applications. In this work, time-resolved electrical behaviour of these devices has been obtained through a set of systematic measurements. The electrical equivalent circuit has been derived, a number of simulations at different frequencies have been performed using commercial software for analogue circuits. Performance of this electrical model to account for time domain variations of switching currents in chiral smectic LC displays with V/W-shaped electrooptical response has been analyzed as well.
9
Content available remote Synthesis and properties of high tilted antiferroelectric esters with partially fluorinated alkoxyalkoxy terminal chains
Żurowska M., Dąbrowski R., Dziaduszek J., Czupryński K., Skrzypek K., Filipowicz M., Bennis N., Otón J. M.
Opto-Electronics Review
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2008
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Vol. 16, No. 3
251-256
EN
Novel chiral esters with partially fluorinated alkoxyalkoxy terminal chains are described. Their phase transition temperatures, enthalpies, and electrooptical properties are reported. A helical pitch in pure compounds and their mixtures based on selective reflection of light is also characterized.
10
Content available remote Orthoconic antiferroelectric liquid crystals containing biphenyl, terphenyl, or naphthyl mesogenic unit
Dąbrowski R., Drzewiński W., Dziaduszek J., Gąsowska J., Henderson P. A., Kula P., Otón J. M., Bennis N.
Opto-Electronics Review
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2007
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Vol. 15, No. 1
32-36
EN
Three homologous series of orthoconic (45 degree tilt) antiferroelectric liquid crystals containing either naphthyl or terphenyl groups as mesogenic unit have been synthesized and their mesomorphic behaviour investigated by DSC and polarized light microscopy, and their properties discussed. X-ray difraction studies have shown the presence of a de Vries-type smectic A phase which does not exhibit a layer shrinkage on transition to the ferroelectric smectic C phase. Mixtures of the new materials have been formulated and their electro-optical properties investigated for their use in surface stabilized orthoconic antiferroelectric liquid crystal (SSOAFLC) devices.
11
Content available remote Modifying electrooptics of orthoconic antiferroelectric liquid crystal cells by manufacturing procedures
Spadło A., Bennis N., Dąbrowski R., Quintana X., Otón J. M., Geday M. A.
Opto-Electronics Review
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2007
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Vol. 15, No. 1
60-65
EN
Orthoconic antiferroelectric liquid crystals (AFLCs) having 45° tilt angle have been proposed to overcome the problem of reduced contrast usually exhibited by regular antifrerroelectric displays. However, the pitch of the helix induced by chrality is customarily short in existing orthoconic materials, making it difficult to achieve surface stabilized configurations when the material's pitch is amaller than the cell thickness.In this work, the influence of different manufacturing procedures on the electrooptical behaviour of orthoconic AFLCs is studied. Using the same arthoconic AFLC mixture, aligning surfaces and manufacturing protocol, we have observed two dissimilar responses, true orthoconic behaviour; and orthoconic V-shape response. The electrooptical response depends ultimately on the rubbing strategy adopted in either case.
12
Content available remote Low threshold voltage asymmetric antiferroelectric liquid crystal cells
Bennis N., Spadło A., Dąbrowski R., Martinelli E., Galli G., Quintana X., Otón J. M., Geday M. A.
Opto-Electronics Review
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2006
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Vol. 14, No. 4
281-285
EN
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.
13
Content available remote Design and simulation of single-electrode liquid crystal phased arrays
Bellini B., Geday M. A., Bennis N., Spadło A., Quintana X., Otón J. M., Dąbrowski R.
Opto-Electronics Review
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2006
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Vol. 14, No. 4
269-273
EN
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.
14
Content available remote Video-rate multiplexed driving scheme for passive antiferroelectric liquid crystal displays
Quintana X., Castillo P. L., Otón J. M., Bennis N., Lara A., Urruchi V., Dąbrowski R.
Opto-Electronics Review
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2004
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Vol. 12, No. 3
291-297
EN
Antiferroelectric liquid crystals have been applied to high-end multiplexed displays. The interest on these materials chiefly comes up from their capability of being multiplex addressed with no need of active matrices. Antiferroelectric grey levels arise from a double symmetric hysteresis loop that can be stabilized by a constant holding voltage. Driving schemes are compatible with passive multiplexing, but limitations appear when the multiplexing rate increases. To avoid these limitations, new driving schemes for high multiplexing level at video rate have been designed. The problem of accumulated voltage on bias level arising from data voltages is tackled as well.
15
Content available remote Antiferroelectric liquid crystal displays
Otón J. M., Quintana X., Castillo P. L., Lara A., Urruchi V., Bennis N.
Opto-Electronics Review
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2004
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Vol. 12, No. 3
263-269
EN
In the last few years, the unique features of antiferroelectric liquid crystals (AFLCs) have been explored to develop high-end displays. A number of passive- and active-matrix prototypes have been presented. However, although their use in a number of application areas has been suggested, no commercial products have been announced yet. This work reviews the state of the art of AFLC displays, the reasons for their present low incidence in display markets, and the latest developments aiming to overcome the main shortcomings that hinder their development. V-shape smectic displays are also included in this study. Although not considered strictly antiferroelectrics nowadays, V-shape materials behaviour and scope are similar to traditional AFLCs.
16
Induced Antiferroelectric Phases in Multicomponent Systems
Dąbrowski R., Otón J. M., Urruchi V., Gayo J. L., Czupryński K., Gauza S.
Polish Journal of Chemistry
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2002
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Vol. 76 / nr 2-3
331-344
EN
Materials with induced antiferroelectric phase (SmCA * ) composed of components having synclinic (SmC* _) or orthogonal (SmA) phases have been studied. The characterization included profiles of light transmission curves, response times, threshold, saturation and holding voltages, grey scale, static and dynamic contrast ratio and cone angle between (+) and (-) ferroelectric states. The mixture A70-B30 showed V-shaped (thresholdless) switching, while the mixture 115-C85 showed a threshold with a broad hysteresis curve of tristate antiferroelectrics.
17
Content available remote Antiferroelectric and V-shape liquid crystal on silicon microdisplays
Otón J. M., Dąbrowski R., Quintana X., Urruchi V, Gayo J. L.
Opto-Electronics Review
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2002
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Vol. 10, No. 1
17-21
EN
In this work, the use of antiferroelectric and V-shape liquid crystals for video projection using LCOS microdisplays has been explored. Antiferroelectric grey levels arise from a double symmetric hysteresis loop that can be stabilised by a constant holding voltage, thus an active matrix is not strictly required in this case. If used, then the voltage levels and the waveform must be adjusted to fulfil the voltage limitations dictated by the matrix. V-shape materials lack hysteresis ; therefore the active matrix is mandatory to stabilise the levels. Voltage limitations, however, are less restrictive int his case, since V-shape smectics require just a few volts for full switching.
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