Security devices based on liquid crystals doped with a colour dye

Carrasco Vela, Carlos and Quintana Arregui, Patxi Xabier and Otón, E. and Geday, Morten Andreas and Otón Sánchez, José Manuel (2011). Security devices based on liquid crystals doped with a colour dye. "Opto-Electronics Review", v. 19 (n. 4); pp. 496-500. ISSN 1896-3757. https://doi.org/10.2478/s11772-011-0049-8.

Description

Title: Security devices based on liquid crystals doped with a colour dye
Author/s:
  • Carrasco Vela, Carlos
  • Quintana Arregui, Patxi Xabier
  • Otón, E.
  • Geday, Morten Andreas
  • Otón Sánchez, José Manuel
Item Type: Article
Título de Revista/Publicación: Opto-Electronics Review
Date: September 2011
ISSN: 1896-3757
Volume: 19
Subjects:
Freetext Keywords: liquid crystal – security device – dichroic dye – absorption – polarized light – latent image
Faculty: E.T.S.I. Telecomunicación (UPM)
Department: Tecnología Fotónica [hasta 2014]
Creative Commons Licenses: Recognition - No derivative works - Non commercial

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Abstract

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.

More information

Item ID: 11308
DC Identifier: http://oa.upm.es/11308/
OAI Identifier: oai:oa.upm.es:11308
DOI: 10.2478/s11772-011-0049-8
Official URL: http://www.springerlink.com/content/r0645958237um213/
Deposited by: Memoria Investigacion
Deposited on: 03 Jul 2012 08:46
Last Modified: 20 Apr 2016 19:25
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