Wyniki wyszukiwania - Biblioteka Nauki

1

Mathematical model of light propagation through liquid crystal display working under real conditions

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Olifierczuk M.

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tom Vol. 16, No. 3

287-296

EN

The main aim of our work is to present a theory of light propagation through a liquid crystal display worked out in our University. This theory takes into account real conditions of a display operation such as temporal coherence of light source, interference phenomena, spectral characteristics of refractive coefficients of individual layers and their complex forms, real directions of ordinary and extraordinary wavevectors into each layer, real directions of light polarization into anisotropic or dichroic layers etc. Therefore, our theory can be used to determine optical parameters of a liquid crystal display operating under real or at least quasi-real conditions. Contrary to other theories (e.g., Beremann or geometric optics approximation), this model is characterized by a small number of simplifications. Thus, it can be used to analyse a display operating in special conditions, such as military or out-door applications. In these cases, very high optical parameters (luminance and contrast ratio) are needed. Application of even small simplifications conducts to significant changes of calculated parameters.

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Significante of reflection reduction in a TN display for colour visualisation

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Olifierczuk M. , Zieliński J.

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2002

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tom Vol. 10, No. 1

35-37

EN

This paper contains the results of theoretical considerations about light propagation through the real TN display working in reflective and negative mode. This mode provides us with a possibility to obtain a colour image. We have done mathematical and numerical analyses of a propagation of light wave through liquid crystal (LC) displays with antireflective layer, glass planes, conductive layers, LC layer and polarisers. We have taken into account real conditions of a display operation, i. e., spectral properties of all components, optical anisotropic and dichroic properties of LC layer, reflections from all phase borders and also spectral characteristics of light source and sensitivity of human eye.

3

Fotoporządkowanie : alternatywna technika dla szybkich przetworników ciekłokrystalicznych

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Chrzanowski M. M. , Zieliński J. , Nowinowski-Kruszelnicki E. , Olifierczuk M.

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2010

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tom Vol. 59, nr 3

375-394

PL

W artykule podjęto temat wyboru techniki fotoporządkowania ciekłego kryształu. Technologia ta jest alternatywą dla najczęściej stosowanego rubbingu, czyli jednostronnego polerowania warstw poliimidowych i poliamidowych. Zarówno w przypadku rubbingu (buffingu), który ma naturę kontaktową, jak i bezkontaktowego fotoporządkowania efektem pracy jest wytworzenie anizotropii warstwy, która następnie ma za zadanie porządkować leżącą bezpośrednio na niej warstwę ciekłego kryształu (LC). Rubbing jest metodą stosunkowo prostą i tanią i jest zwyczajowo używany przy produkcji wyświetlaczy ciekłokrystalicznych. W trakcie polerowania mogą jednak powstawać uszkodzenia struktury matrycy aktywnej oraz tworzyć się pyły, które są szkodliwe zwłaszcza dla bardzo cienkich warstw ciekłego kryształu. W związku z tym poszukuje się metod alternatywnych porządkowania. Z fotoporządkowaniem mamy do czynienia wtedy, gdy anizotropia warstwy porządkującej wywołana jest przez ekspozycję materiału fotoczułego na działanie światła ultrafioletowego spolaryzowanego liniowo. Jest to proces bezkontaktowy, więc eliminuje on większość wymienionych wcześniej wad rubbingu. Ponadto umożliwia pracę na plastycznych oraz zakrzywionych podłożach. Istnieją cztery różne drogi realizacji procesu fotoporządkowania warstwy światłoczułych materiałów organicznych: 1) fotodegradacja w materiałach poliimidowych, 2) izomeryzacja cis-trans azozwiązków, 3) czysta reorientacja związków azowych w polu potencjału światła UV oraz 4) sieciowanie w strukturze polimerowej. W pracy przedstawiono krytyczny przegląd wyżej wymienionych metod. Zastosowanie fotoporządkowania badane jest pod kątem przydatności w komórkach działających w oparciu między innymi o efekty: FLC (ang. ferroelectric liquid crystal, ciekły kryształ ferroelektryczny), TN (ang. twisted nematic, skręcony nematyk), BTN (ang. bistable twisted nematic, bistabilny skręcony nematyk), VAN (ang. vertical alignment nematic, pionowa deformacja fazy nematycznej), IPS (ang. in plane switching, przełączanie w płaszczyźnie) i inne. Celem poniższej pracy jest porównanie i określenie przydatności różnych metod fotoporządkowania dla technologii przetworników ciekłokrystalicznych o dużej jasności zobrazowania.

EN

In this study we consider the topic of the photoalignment of liquid crystal material. It is an alternative method to the rubbing of polyimide and polyamide layers. Both techniques provide the anisotropy in organic layers. This anisotropy aligns overlaying liquid crystal. The rubbing is a well known and cheap technique and it's ordinarily used in liquid crystal displays manufacturing. However, it has several disadvantages, for example it produces dust particles and charges the layer. Furthermore it may damage the surface electronic. These drawbacks can be critical factors in working with thin liquid crystal layers (about 2-5 µm) for example ferroelectric and antiferroelectric Lcs. Heterogeneity at the microscopic level can be noxious especially in the area of some types of liquid crystals and in manufacturing high-resolution liquid crystal displays (over 40”) and state-of-art projector display systems. In order to omit these problems, very important for the future work is to develop a new, universal and high-performance, technique for liquid crystal aligning. One of alternatives is photoalignment. It eliminates many of drawbacks mentioned above. This technique uses light (generally linearly polarized ultraviolet light, LPUV) to produce anisotropy in photodephiniable materials. In addition this technique allows us to obtain layers on plastic or curve surfaces. We can distinguish four main photoalignment mechanisms (including photo-chemical reactions and photo-physical changes): (1) cis-trans isomerization in azo-structures: pure dyes films, polymers containing azo-groups and monolayers of azodyes, (2) pure reorientation of photo-chemically stable azo-dyes molecules, (3) photodegradation in polyimide materials and (4) crosslinking in cinnamoyl and coumarin side-chain polymers. There are some modifications among these procedures, such as polymerizable azo-dyes or Langmuir-Blodgett films. Photoalignment is investigated in diverse liquid crystal modes, such as: twisted nematic (TN), vertical alignment (VAN), in plane switching (IPS) and many others. In this paper we describe all of the photoalignment mechanisms mentioned above and compare their ability to align the liquid crystal material in the field of application in various modes of LC cells.

4

Photoalignment - an alternative aligning technique for Liquid Crystal Displays

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Chrzanowski M. M. , Zieliński J. , Olifierczuk M. , Kędzierski J. , Nowinowski-Kruszelnicki E.

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2011

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tom Vol. 48, nr 1

7--13

EN

Purpose: The main aim of this work is to present our investigation in the field of photoalignment. In this work we introduce useful photoalignment techniques and discuss in detail the results of photocrosslinking and photodegradation in photosensitive polymer materials. Design/methodology/approach: We describe the new procedure investigated in our laboratory for the following materials: HD-4100, HD-4110 and HD-8820 (DuPont Microsystems) as well as the characteristics obtained for the thin polyimide layers: optical homogeneity, thickness, surface tension. Findings: Polyimide layers obtained on the glass/ITO substrates which were irradiated using linearly polarised ultraviolet light show the aligning properties for liquid crystal layers. The proposed new technology is fairly fine to obtain 2-3 cm2 layers. Research limitations/implications: The liquid crystal material alignment quality is not perfect, but the works are still in progress. In the next step we will try to use silan-derivative adhesion promoters to lower the aligning layers thickness. This solution will probably also have a big influence on the aligning layers homogeneity. Practical implications: We discuss an alternative technique of the rubbing method for composition of liquid crystal displays. Liquid crystal displays are widely used for many industrial and commercial applications. Multimedia and graphics and medical-imaging systems require top quality images. Such an image can be obtained under the condition of good liquid crystal alignment. Rubbing is a method conventionally used for these purposes. Unfortunately this technique has some disadvantages that are particularly visible in new generation displays. The usage of photodephiniable materials opens the route to obtain an appropriate molecular tilt and controlled anchoring energy as well as preparing layers that are suitable to providing diversified optical axes in one liquid crystal cell. Originality/value: Agents investigated in the paper hasn’t been used as the alignment materials in liquid crystal cells preparation so far. The used technology as well as HD-4100, HD-8820 and HD-4110 materials are suitable as the alternative substances for common used aligning chemical substances and technologies.

5

Transparent laser damage resistant nematic liquid crystal cell “LCNP3”

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Raszewski Z. , Piecek W. , Jaroszewicz L. , Dąbrowski R. , Nowinowski-Kruszelnicki E. , Soms L. , Olifierczuk M. , Kędzierski J. , Morawiak P. , Mazur R. , Miszczyk E. , Mrukiewicz M. , Kowiorski K.

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2014

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tom Vol. 22, No. 3

196-200

EN

There exists the problem in diagnostics of dense plasma (so-called Thomson diagnostics). For this purpose the plasma is illuminated by series of high energy laser pulses. The energy of each separate pulse is as large as 3 J, so it is impossible to generate a burst of such pulses by a single laser. In this situation, the pulses are generated by several independent lasers operating sequentially, and these pulses are to be directed along the same optical path. To form an optical path with ʎ = 1.064 μm and absolute value of the laser pulse energy of 3 J, a special refractive index matched twisted Nematic Liquid Crystal Cell of type LCNP3, with switching on time ƮON smaller than 3 μs was applied.

6

Refractive index matched half-wave plate with a nematic liquid crystal for three-dimensional laser metrology applications

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Piecek W. , Jaroszewicz L. R. , Miszczyk E. , Raszewski Z. , Mrukiewicz M. , Perkowski P. , Nowinowski-Kruszelnicki E. , Zieliński J. , Olifierczuk M. , Kędzierski J. , Sun X. W. , Garbat K. , Kowiorski K. , Morawiak P. , Mazur R. , Tkaczyk J.

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tom Vol. 24, No. 4

169--182

EN

There exists a need in a quality and accuracy of a three-dimensional laser metrology operating in numerically controlled automatic machines. For this purpose, one sends three laser beams mutually perpendicular. These three beams of the wavelength λ = 0.6328 μm are generated by the same laser and are directed along three independent, orthogonal, mutually perpendicular, optical paths with a given light polarization plain. Using these beams, constituting the frame of coordinates, three independent laser rangefinders are able to determine spatial coordinates of a working tool or a work piece. To form these optical pulses, a special refractive index matched Half-Wave Plate with nematic Liquid Crystal (LCHWP) was applied. The presented half-wave plate is based on a single Twisted Nematic (TN) cell (with the twist angle φ = π/2) of a rather high cell gap d ~15 μm filled with a newly developed High-Birefringence Nematic Liquid Crystal Mixture (HBLCM) of optical anisotropy as high as ∆n ~0.40 at λ = 0.6328 μm, where the Mauguin limit above 5.00 ~ ∆nd >> λ/2 = 0.32 is fulfilled.

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Measurement of elastic constants of nematic liquid crystals with use of hybrid in-plane-switched cell

26%

Nowinowski-Kruszelnicki E. , Kędzierski J. , Raszewski Z. , Jaroszewicz L. , Kojdecki M. A. , Piecek W. , Perkowski P. , Olifierczuk M. , Miszczyk E. , Ogrosnik K. , Morawiak P.

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tom Vol. 20, No. 3

255-259

EN

A new method for quick and pretty accurate measurements of splay, twist and bend elastic constants of nematic liquid crystals is experimentally verified. The main concept relies on exploiting only the electric field and determining magnitudes of nematic elastic constants from threshold fields for Freedericksz transitions in only one hybrid in-plane-switched cell. In such cell the deformations of an investigated liquid crystal are controlled by three separated pairs of electrodes confining measurement domains. In two of them inter-digital electrodes are mounted on one cell cover. Splay, twist and bend elastic constants can be measured by a proper choice of electrodes' configuration together with orienting cover coatings (without applying magnetic fields). In this paper, we describe layout of our cells and results of experimental tests by using different liquid crystals: 5CB and 6CHBT (with positive dielectric anisotropy), Demus' esters (with negative dielectric anisotropy) and new liquid crystals mixtures produced in our university.