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A Terahertz Polarizer Based on Multilayer Metal Grating Filled in Polyimide Film

Terahertz (THz) polarizers with low reflection and absorption loss and high polarization extinction ratio (PER) based on multilayer metallic gratings filled in a polyimide film were studied theoretically and experimentally. In theory, THz polarization transmittance and PER of single-layer and multilayer polarizers at different THz frequencies were simulated, and their variations with the layer number of the metallic grating structure were discussed. With the increase in the layer number, PER increases prominently due to the evanescent wave coupling between different layers. In the experiment, a double-layer polarizer with an effective diameter of 42.3 mm was fabricated via layered imidization processes and evaluated by the THz time-domain spectroscopy measurements. Results showed that an average transmittance of 80.5% and a maximal PER of 70 dB were achieved, which were in good agreement with the simulated results and were compared with or outperformed most reported single- or double-layer polarizers.