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1

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.

2

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.

3

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.

4

Mesomorphic, dielectric, and optical properties of fluorosubstituted biphenyls, terphenyls, and quaterphenyls

Kula P., Spadło A., Dziaduszek J., Filipowicz J., Dąbrowski R., Czub J., Urban S.

Opto-Electronics Review

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2008

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Vol. 16, No. 4

379-385

EN

Compounds with moderate and large negative dielectric anisotropy (Δ ε ) are very attractive liquid crystal (LC) for vertical alignment mode (VA). Materials with such properties can be achieved by lateral substitution of a polar group into a mesogenic molecule. We synthesized some new LC materials with a negative value of Δ ε, a moderately high birefringence (Δ n), and a low viscosity. The mesomorphic and physical behaviour of the novel biphenyls, terphenyls and quaterphenyls fluorosubstituted in the rigid core and also with fluorinated alkyl and alkoxy chains are investigated. The prepared series of four LC compounds are promising for new LC mixtures for various applications. Examples of nematic mixtures with Δ ε ∼ -3.25 will be presented.

5

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.

6

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.

7

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.