Tunable light diffractor associated with liquid crystal molecular reorientation from homogeneous alignment to periodic twist deformation in micrometre scale

Abstract

We have demonstrated the formation of a transmissive tunable light diffractor with a fine grating period using a fringe-field switching (FFS) device. The presented device operates as a superposed amplitude and phase grating. The phase grating is formed by a thin slab of a nematic liquid crystal (LC) film and the amplitude grating is constructed by the electrode pattern of the FFS device. The electrode-position-dependent periodic deformation of the LC director as a function of the applied electric field is analysed and the respective occurrence of phase difference in monochromatic, coherent, linearly polarized He–Ne (632.8 nm) laser light is also calculated using the Jones matrix method at operating voltage. The same calculation results show that the transmitted beam of the present FFS diffractor is right-handed elliptically polarized. The operation characteristics of the thin diffracting device are investigated using a He–Ne laser source and a photodetector which shows a significantly large angular deviation of the diffracted beam owing to the small periodicity of LC deformation.