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Polarizing back- and frontlight for LCD based on liquid crystal polymer film and a process to manufacture Disclosure Number: IPCOM000010098D
Publication Date: 2002-Oct-22
Document File: 4 page(s) / 102K

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Polarizing back- and frontlight for LCD based on liquid crystal polymer film and a process to manufacture

A polarization-selective waveguide that emits collimated light of a single polarization is disclosed. The waveguide may be applied as an edge-lit back-light or front-light in for example a liquid crystal display. An embodiment of such a waveguide is shown in Figure 1.

The waveguide shown in Fig. 1 comprises an optically isotropic waveguiding substrate onto which an optically anisotropic, more in particular, a birefringent layer 5 is laminated. The layer 5 has a relief structured major surface facing away from the substrate 3. On top of the relief structured surface an optically isotropic layer 7 is provided which planarizes the relief structured surface.

The refractive index of the layer 7 is substantially matched to the ordinary refractive index of the anisotropic layer 5 but different from the extraordinary refractive index thereof. The relief structured surface is structured such that given the difference in refractive index an extraordinary light beam experiences is reflected at the relief structured surface with high efficiency towards the exit surface of the waveguide.

In operation, a beam of light from a light source (not shown) arranged near a side face of the waveguide (here the left hand side) is coupled into at least the waveguiding substrate 3. P-polarized light beam component is waveguided down the waveguide substantially whereas the s-polarized light beam component is reflected by the relief-structured surface towards the exit surface when incident thereon and subsequently coupled out of the waveguide.

As it travels down the waveguide the p-polarized light beam component becomes depolarized due to optical imperfections present in the waveguiding substrate thus making available s-polarized light beam component for outcoupling.

Thus, a waveguide providing polarized light with high efficiency is obtained.

Such a waveguide may be manufactured as follows:

A polyester film, for instance polyethylene terephthalate (PET) is stretched to a draw ratio of 4.5 leading to high refractive index along the stretching direction (ne=1.67) and a low refractive index perpendicular to it (no=1.53). The anisotropic PET is provided with microstructures according to Figure 1 by micro-machining (micro-milling). This anisotropic film is adhered to a 1 mm polycarbonate waveguiding substrate (niso, waveguide=1.585) by means of an UV adhesive (nadhesive = 1.585). The anisotropic PET layer is covered with an isotropic layer, e.g. consisting of an UV curing acrylate mixture with a refractive index of the cured state of 1.53, matching the ordinary index of the PET, taking where care that the indentations created by the relief-structured surface microstructures are completely filled. 


A drawback of this method of manufacturing of the device is the large number of processing steps the method comprises. A further drawback is the use of micro-machining, as mic...