In the design and development of Liquid Crystal on Silicon (LCoS), one can predict possible problems and propose
according solutions with calculating the director and optical characteristics of the liquid crystal. The optical property of
LCoS is calculated with the Finite-Difference Time-Domain Method (FDTD) in this paper. The diffraction characteristics
are exactly analyzed with incident plane wave and the computational space terminations are provided by a combination
of the perfectly matched layer (PML) and periodic boundary conditions (PBC). The influences on optical properties of
LCoS with different interpixel gap, pretilt angle and thickness are studied. The result shows that diffraction efficiency is
greatly affected by the thickness of cell. It’s significant and offer reference for the design and manufacture of LCoS.