A Low Voltage Liquid Crystal Phase Grating with Switchable Diffraction Angles

Abstract

We demonstrate a simple yet high performance phase grating with switchable diffraction angles using a fringe field switching (FFS) liquid crystal (LC) cell. The LC rubbing angle is parallel to the FFS electrodes (i.e. α = 0°), leading to symmetric LC director distribution in a voltage-on state. Such a grating exhibits three unique features: 1) Two grating periods can be formed by controlling the applied voltage, resulting in switchable diffraction angles. In our design, the 1^st diffraction order occurs at 4.3°, while the 2^nd order appears at 8.6°. 2) The required voltage to achieve peak diffraction efficiency (η~32%) for the 1^st order is only 4.4 V at λ = 633 nm as compared to 70 V for a conventional FFS-based phase grating in which α ≈ 7°, while the 2^nd order (η~27%) is 15 V. 3). The measured rise and decay time for the 1^st order is 7.62 ms and 6.75 ms, and for the 2^nd order is 0.75 ms and 3.87 ms, respectively. To understand the physical mechanisms, we also perform device simulations. Good agreement between experiment and simulation is obtained.