A method of optimising the filter bandwidth of a spatially modulated full-polarisation imaging system

In this study, a method of calculating the optimal filter bandwidth based on the watermark fringes of simulation interference was proposed to maintain the optimal performance of a spatially modulated full-polarisation imaging system in different target scenes, offering some theoretical guidance for the type selection of the imaging lens for the system. The two-dimensional sine function of the watermark fringes of simulation interference was superimposed on the intensity image, and a full-polarisation image was obtained by demodulating the simulation interferogram using the fast Fourier transform and the frequency-domain low-pass-filtering algorithm. Then, the polarisation image with the highest structural similarity to the intensity image was solved, and a method of calculating the optimal filter bandwidth based on the improved elitist clonal selection algorithm (ECSA) was presented. Next, the optimal focal length of the imaging lens was calculated in combination with the image resolutions, incident light wavelengths, and Savart polariser single-beam offsets selected in different target scenes, to complete the theoretical type selection. The experimental results showed that the spatially modulated full-polarisation imaging system constructed based on the optimal filter bandwidth had a good performance; and that, compared with empirical type selection, the proposed type selection based on the optimal filter bandwidth increased the spectral inversion area by 4.2 times and the image structural similarity by 71 %, significantly improving the polarisation imaging quality of the system.