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Patterning the surface alignment in liquid crystal devices is a highly effective strategy to realize additional functionalities to the liquid crystal electro-optic devices. One example is a switchable diffractive optical device that utilizes polarization/phase grating structures imprinted on the alignment surface. When it is working in the Pancharatnam-Berry phase mode, it is possible to realize a perfect beam diffraction without the loss of energy into higher order diffractions. In order to apply this attractive technology to a practical device, a drawback often encountered is the low throughput of the fabrication of such fine patterns with a spatial resolution comparable to the light wavelength, irrespective of the fabrication techniques employed. The purpose of this presentation is to describe an efficient scheme for fabricating fine polarization patterns over a large area based on the unique property of the Pancharatnam-Berry phase itself. We refer this scheme as “recursive photoalignment,” since the photoaligned pattern is used as the photomask for the subsequent photoalignment step; each step of photoalignment in this way allows us to prepare an enlarged pattern by a linear factor of 2, while maintaining the pattern resolution always the same as the original pattern. We demonstrated the feasibility of this technique by fabricating a 50mmX50mm photoalignment pattern with a finest resolution of a few micrometers, starting from a 2mmX2mm master pattern fabricated by a DMD-based maskless photoalignment processor. Although there are certain limitations on the type of pattern for this method to work, it also opens up a new opportunity to synthesize large area-fine resolution patterns from a less technically demanding photoalignment pattern.
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