Liquid-Crystal Blazed Gratings with Spatially Distributed Pretilt Angle

An electrically tunable liquid-crystal (LC) blazed grating was demonstrated by introducing a periodic pattern of pretilt angle that was controlled by adjusting the rubbing density. In the proposed LC grating, an asymmetrically varying LC molecular orientation was realized even without voltage application. The diffracted light intensity was controlled by adjusting the applied voltage, and the diffraction effect disappeared under a sufficiently high applied voltage. Asymmetric diffraction patterns were obtained and it was revealed that 0th-, 1st-, and 2nd-order diffraction beams can be switched with an appropriate applied voltage. A maximum diffraction efficiency of 0.68 for the 1st-order diffraction was experimentally obtained; however, it is much less than the theoretical limit of unity. It is likely that the difference between optical path lengths for extraordinary and ordinary rays is not linearly distributed. (C) 2010 The Japan Society of Applied Physics DOI: 10.1143/JJAP.49.061701