Spatial filters based on azo-dye-doped liquid crystal films

Abstract

This investigation researches and developes two spatial filters based on dye-doped liquid crystal films. One is made with a dye-doped liquid crystal (DDLC) film, and is polarization controllable. The other is transflective, and is fabricated with an azo dye doped cholesteric liquid crystal (DDCLC) film. The fabrication of the former type relies on the fact that the various intensities of the diffracted orders are responsible for various changes of the polarization state induced by the photo-aligned DDLC film. Particular spatial orders in the Fourier optical signal process can be filtered using an analyzer placed behind the sample by controlling the polarization state of the diffracted orders. The latter is based on the photoisomerization effect in a DDCLC film with a concomitant lowering of phase transition temperature from a cholesteric to an isotropic phase (T_Ch-I). The fabrication relies on the fact that the various intensities of the diffracted orders are responsible for various degree of transparency induced by the photoisomerized DDCLC film. Particular spatial orders in the Fourier optical signal process can be filtered to trans- or reflect- part at the same time. Simulations are also performed for the two-type spatial filters, and the results agree closely with experimental data.