In order to research the effect of the periodic structure on the performance of grating light modulator(GLM),a model of GLM with alterable periodic structure is built,and the digital image processing method in MATLAB software is used.First,based on Fourier transform,the light field distribution on the spectrum plane and image plane of two kinds of GLM with different periodic structures is analyzed,and the influence of different periodic structures on the contrast of modulation is calculated and tested.The r...