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Characteristic functions for uniformly twisted birefringent media
Dalarna University.
Swedish LCD Center AB.
Labotarory of Applied Optics, Department of Physics, Chemistry and Biology, Linköping University.
Hong Kong University of Science and Technology, Kowloon, Hong Kong.
2007 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 102, no 6, 063110-1-063110-7 p.Article in journal (Refereed) Published
Abstract [en]

We present two functions for characterization of birefringent media with application to twisted nematic liquid crystal (LC) cells in the field off state. The first function is for reflective LC cells and the second is for transmissive LC cells. Based on the Stockes formalism, it is shown that these functions describe the ability of a layer of the twisted birefringent medium to change polarization of the output light and are invariant to the layer orientation. The characteristic functions are found in simple procedures and can be used for simultaneous determination of retardation, its wavelength dispersion, and twist angle, as well as for solving optimization problems.

Place, publisher, year, edition, pages
2007. Vol. 102, no 6, 063110-1-063110-7 p.
Keyword [en]
reflective liquid crystal displays, LCD
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-107497DOI: 10.1063/1.2781300OAI: oai:DiVA.org:uu-107497DiVA: diva2:231479
Available from: 2009-08-13 Created: 2009-08-13 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Optical Characterization and Optimization of Display Components: Some Applications to Liquid-Crystal-Based and Electrochromics-Based Devices
Open this publication in new window or tab >>Optical Characterization and Optimization of Display Components: Some Applications to Liquid-Crystal-Based and Electrochromics-Based Devices
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This dissertation is focused on theoretical and experimental studies of optical properties of materials and multilayer structures composing liquid crystal displays (LCDs) and electrochromic (EC) devices.

By applying spectroscopic ellipsometry, we have determined the optical constants of thin films of electrochromic tungsten oxide (WOx) and nickel oxide (NiOy), the films’ thickness and roughness. These films, which were obtained at spattering conditions possess high transmittance that is important for achieving good visibility and high contrast in an EC device.

Another application of the general spectroscopic ellipsometry relates to the study of a photo-alignment layer of a mixture of azo-dyes SD-1 and SDA-2. We have found the optical constants of this mixture before and after illuminating it by polarized UV light. The results obtained confirm the diffusion model to explain the formation of the photo-induced order in azo-dye films.

We have developed new techniques for fast characterization of twisted nematic LC cells in transmissive and reflective modes. Our techniques are based on the characteristics functions that we have introduced for determination of parameters of non-uniform birefringent media. These characteristic functions are found by simple procedures and can be utilised for simultaneous determination of retardation, its wavelength dispersion, and twist angle, as well as for solving associated optimization problems.

Cholesteric LCD that possesses some unique properties, such as bistability and good selective scattering, however, has a disadvantage – relatively high driving voltage (tens of volts). The way we propose to reduce the driving voltage consists of applying a stack of thin (~1µm) LC layers.

We have studied the ability of a layer of a surface stabilized ferroelectric liquid crystal coupled with several retardation plates for birefringent color generation. We have demonstrated that in order to accomplish good color characteristics and high brightness of the display, one or two retardation plates are sufficient.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 64 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 664
Keyword
ellipsometry, liquid crystal, LCD, optical anizotropy, electrochromic, inverse problems
National Category
Atom and Molecular Physics and Optics Atom and Molecular Physics and Optics Computational Mathematics
Research subject
Solid State Physics; Information Systems
Identifiers
urn:nbn:se:uu:diva-107429 (URN)978-91-554-7583-3 (ISBN)
Public defence
2009-09-24, 2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2009-09-03 Created: 2009-08-11 Last updated: 2009-09-03Bibliographically approved

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Valyukh, Iryna

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