LIQUID-CRYSTALLINE FILMS FOR FIBER OPTIC SENSING OF HIGH HYDROSTATIC-PRESSURE

In this paper we present a further development of a fiber optic method for high hydrostatic pressure sensing utilizing liquid crystalline fi lms as a sensing element. The method exploiting the effect of pressure -induced changes in the wavelength of selective Bragg light reflection observed in ordered layers of a chiral nematic liquid crystal resides in guiding a light beam of predetermined wavelength toward the layers using optical fibers and collecting the light beam reflected by the l ayers via another of optical fibers. The purpose of the study was to o btain liquid crystalline films which would be particularly sensitive f or pressure effects and in which disturbing effects of temperature wou ld be minimized. To achieve this goal two classes of chiral nematic li quid crystals have been investigated: the first class was composed of a nematic liquid crystal and a mixture of three chiral dopants preset for selective Bragg reflection conditions, while the second class was preset for the Mauguin limit to obtain rotation of linear polarization of light coming through the liquid crystalline film. The results indi cate that both classes of the investigated liquid crystalline films of fer high response to pressure with a minimized temperature sensitivity .