Nanoporous alumina films for display devices

Anisotropic optical properties of free nanoporous anodic alumina films transparent in the visible spectrum for the restricted range of pore diameters and pore intervals are discussed. The basic experimental procedure is presented for the production of these films. Diagrams of elastic light scattering in two-dimensional nanoporous alumina structures demonstrated anisotropy due to the spatial distribution of the photon density of states because of the photonic band gap formation in materials with a periodic change of the refraction index on the scale of the wavelength. A birefringence value (the difference in the normal and tangential refraction indices) was found from the measurements and computer modeling to be up to 0.08. Light scattered along pores was experimentally found to have a polarization perpendicular to the polarization of the incident light. The results obtained show that the nanoporous structure of anodic alumina films can be purposefully used to control a light propagation, namely, to perform anisotropic light scattering in LCD backlight systems as well as potential modification of light polarization.