Periodic reverse-twist nematic domains obtained by microrubbing patterns

A method for forming periodic 90degrees reverse-twist domains using a microscale rubbing pattern has been proposed; that is, an isolated 90degrees twist domain is surrounded by a 45degrees twist domain. Since liquid crystal (LC) materials exhibit elastic nature, the twist sense of the inner 90degrees twist domain prefers to be the same as that of the surrounding 45degrees twist domain. Two factors are investigated to obtain periodic 90degrees reverse-twist domains; (i) the injection process of LC material (isotropic or nematic phase) and (ii) the ratio of the area of the surrounding 45degrees twist domain and the whole area (the normalized area of the 45degrees twist domain). In the case of the injection in isotropic phase, it is revealed that periodic 90degrees reverse-twist domains can be obtained only when the area of the 45degrees twist domain is sufficiently large. On the other hand, in the case of injection in nematic phase, periodic 90degrees reverse-twist domains can successfully obtained regardless of the area of the 45degrees twist domain. Thus, the injection rocess is a very important factor to obtain periodic 90degrees reverse-twist domains. The fabricated LC cell with the periodic 90degrees reverse-twist domains is applied to LC grating. The almost linear relationship between the diffraction efficiency and the normalized area of the 45degrees twist domain is found and the high diffraction efficiency (0.39) near the theoretically maximum value (0.405) is obtained when the normalized area of the 45degrees twist domain is very small (0.1). The fabricated LC grating can function as a polarization-idependent and wavelength-independent LC grating. (C) 2004 American Institute of Physics.