Diffractive Optics of Anisotropic Polarization Gratings

Diffractive Optics of Anisotropic Polarization Gratings

Xu, M.

Urbach, H.P. (promotor)

Applied Sciences

2009-03-16

Diffraction gratings are being used to manipulate light in many different applications, such as in flat panel display systems, modern lighting systems, and optical recording. Diffraction gratings can be made polarization selective due to form birefringence. An alternative approach to polarization selective gratings is to use birefringent materials. In this thesis, diffraction gratings consisting of at least one birefringent material are investigated. The optical properties of an anisotropic medium follow from its dielectric permittivity tensor. Compared to isotropic media whose dielectric permittivity reduces to a scalar, the permittivity tensor of an anisotropic material on some basis is in general a full 3Ã3 matrix. In most standard textbooks, the treatment of anisotropic materials is restricted to those with symmetric real permittivity tensor. However, in some media, the permittivity tensor is complex hermitian. Cholesteric liquid crystals are examples of such media. In this thesis, we develop a rigorous study of light propagation in anisotropic media with a complex hermitian dielectric permittivity tensor of which the real symmetric tensor is only a special case. In Chapter 2 we study Maxwell's equations for time-harmonic monochromatic plane waves in anisotropic media. We extend the classical theory of a real symmetric permittivity tensor to that of a complex hermitian tensor. In a medium with an hermitian type of permittivity tensor, the eigenstates of the electric field vector are elliptically polarized with opposite directions of rotation. In Chapter 3, gratings consisting of liquid crystal molecules oriented parallel to the grating grooves are studied for application as polarizing color separator in liquid crystal displays. In Chapter 4, we characterize the diffraction efficiencies of so-called POLICRYPS (acronym for Polymer Liquid Crystal Polymer Slices) gratings. A diffraction efficiency of more than 95% can be achieved by limiting the incident angles to the cone defined by the Bragg condition. In Chapter 5 and Chapter 6 photoanisotropic polarization gratings are studied extensively. Photoanisotropic polarization gratings can be manufactured with polarization holographic recording. Two interfering beams are used to make a periodic interference pattern which is then translated into a periodically modulated permittivity tensor, which is complex hermitian in general, using the photoanisotropic material.

diffractive optics
liquid crystal
anisotropy
polarization
diffractive grating
photoanisotropy
birefringence
polarization holography

http://resolver.tudelft.nl/uuid:cb51ea30-08f1-42c0-b696-21b5528697e8

978-90-78314-10-3

Institutional Repository

doctoral thesis

(c) 2009 Xu, M.