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The simulation results show that the transmitted beam are well meet the characteristic of vortex beam, which the transmittance of cross-polarized vortex beam is as high as 64% at 1.48 THz while the phase can cover the range of 1*2π. That is, the presented transmissive vortex beam generators can convert incident circularly polarized beam into a cross-polarized vortex beam carrying orbital angular momentum. The approach demonstrated in this paper which is high conversion efficiency, simple structure, quick response, and has potential applications in the field of terahertz communication.
Base on the dual-band THz passive imaging system which is composed of a 94GHz and a 250GHz cell detector, this paper researched the preprocessing and fusion algorithm for THz dual-band images. Firstly, THz images have such problems: large noise, low SNR, low contrast, low details. Secondly, the stability problem of the optical mechanical scanning system makes the images less repetitive, obvious stripes and low definition. Aiming at these situations, this paper used the BM3D de-noising algorithm to filter noise and correct the scanning problem. Furthermore, translation, rotation and scaling exist between the two images, after registered by the intensity-base registration algorithm, and enhanced by the adaptive histogram equalization algorithm, the images are fused by image fusion algorithm based on wavelet. This effectively reduced the image noise, scan distortion and matching error, improved the details, enhanced the contrast. It is helpful to improve the detection efficiency of hidden objects too. Method in this paper has a substantial effect for improving the dual-band THz passive imaging system’s performance and promoting technology practical.
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