Linear polarizers based on oriented polymer blends

Traditionally, birefringent, double refracting crystals and, more commonly, sheet polarizers based on oriented polymers comprising dichroic additives are employed to generate linearly polarised light. Nowadays, these sheet polarizers are widely used in flat panel displays where they serve a dual purpose; a first polarizer is used to generate linearly polarised light and a second polarizer (analyser) generates visual perception of the switching of the polarisation direction of the light by electro-optical cells containing a twisted nematic or super twisted nematic material. A dichroic polarizer which generates perfectly, linearly polarised light absorbs at least fifty percent of the incident, unpolarized light and this light is transferred into thermal energy. Consequently, the brightness of flat panel displays is limited by the polarizers and the polarizers exhibit excessive heating when used in combination with high intensity light sources (e.g. in projection displays). These limitations of dichroic polarizers have triggered an extensive research effort into new optical components to produce linearly polarised light. Here we introduce uniaxially oriented, polymer blend sheet-polarisers that allow for the generation and analysis of polarised light through anisotropic scattering. By proper selection of materials and processing conditions, phase-segregated polymer blends are produced in which the refractive index of the dispersed phase matches the ordinary refractive index perpendicular to the orientation direction of a birefringent continuous phase, while, simultaneously, a large mismatch exists between the refractive indices parallel to that orientation direction. The refractive index mismatch leads to a scattering of light polarized in this direction and an opaque (white) appearance. The other polarization direction encounters equal refractive indices between the two phases and will therefore be transmitted resulting in a transparent appearance. Thus polarizers are produced based on the selective scattering of one polarization direction with contrast ratios exceeding 1750 in direct transmittance; which, in specific configurations, allow for the recycling of the unwanted (scattered) polarization direction to enhance the efficiency to produce linearly polarized light.