Theoretical characteristics of optical polarizing films using oblique metal island films with distributed island shape

摘要

An oblique metal island (OMI) film is composed of prolate metal nanoclusters inclining to one side. The OMI film has 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. Therefore, the multiplayer of the OMI layers and thin glass layer could be used as an optical polarizing film. In previous works, we have investigated the optical polarizing films using ideal OMI films with uniform aspect ratio of islands for simplification. However, in the OMI films fabricated by using a conventional vacuum evaporation system, the aspect ratio is not uniform. In this paper, we describe the optical polarizing film using the OMI films with distributed island shape. We have calculated the optical characteristics of the OMI films with distributed island shape by assuming that the distribution of aspect ratio of islands is expressed by use of the log-normal function. As the variance of aspect ratio is large, the resonance characteristics become broad. Therefore, it seems that the OMI films with distributed island shape are useful for the wideband optical polarizing films for visible region. By using the OMI films with distributed island shape, we have designed wideband optical polarizing films for 400 - 500 nm by using aluminum and for 620 - 760 nm by using silver as metals. The extinction ratios of designed optical polarizing films are greater than 20 dB.