Design of wideband optical polarizing films for visible region using oblique metal island films

摘要

Wideband optical polarizing films using oblique metal island (OMI) films composed of prolate metal nanoclusters (i.e., islands) inclining to one side has been investigated theoretically. The OMI films exhibit resonance-type absorption in visible region and large optical anisotropy as the resonance wavelengths for the polarization along the shorter and longer axes of the prolate metal nanoclusters are different from each other. In the previous work (OPTO 2006), we proposed an optical polarizing film consisting of the multilayer of the OMI layers and thin glass layers. The proposed optical polarizing films have high heat resistivity in comparison with commercially available polarizing films consisting of dichromatic polymer film as those are made of glass and metal. In this work, we have theoretically investigated wideband optical polarizing films for visible region useful for liquid crystal displays and projectors. Aluminum (Al) is chosen as metal since the Al OMI films have shorter resonance wavelengths from larger plasma frequency of Al. As the resonance wavelength depends not only on the choice of metal but also on the aspect ratio of the prolate islands, the resonance wavelength region of the multilayer consisting of different types of OMI layers with various aspect ratios of islands could be expanded. We have successfully designed the optical polarizing films for shorter wavelength region of 350 - 550 nm by using 7 types of Al OMI layer. The extinction ratio of designed optical polarizing films is greater than 20 dB and insertion loss is less than 0.5 dB. We have also designed the polarizing films for longer wavelength rerion of 600 - 730 nm by using Ag as metal.