This paper is devoted to the analysis of the optical performance of movable-beam grating structures with both lateral and vertical displacement of the beams. We show that in the vector-diffraction domain one can design high- efficiency switches (e.g. between beam transmitter and beamsplitter mode) and modulators for polarized radiation. The devices exhibit a good tolerance to fabrication and mounting errors and a functional flexibility. In addition, by simulating the optical performance of polysilicon micro- electro-mechanical grating structures at a visible wavelength, reported in the literature, we demonstrate that our tools for rigorous electromagnetic simulation of grating structures work well in the scalar-diffraction domain.