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SEM image of a single-layer filter before Si wafer removal. The lattice homogeneity (period of 38 μm) is well-maintained over the whole mesh surface. Inset: close-up of a mesh-cross, squares have been added to improve the adhesion and stability of the mesh wires (width of 500 nm) without influencing the EM response.
Photograph of the single-layer filter mounted onto an annular holder. COC high transparency and sub-μm mesh wires width make the filter hardly visible.
Transmission properties of the mesh filters. Insets are in linear scale. Fig. 4(a) shows the comparison between two single-layer filters with different width w and same period d = 38 μm. The inset reveals a higher transmittance above 1.5 THz for the filter with w = 0.5 μm. Fig. 4(b) shows that multi-layer filters are able to increase the rejection ratio in the stop-band while keeping a high transmittance above 1.5 THz. The red curve (up triangle) and the black curve (dashed) have been reported as a reference and correspond to the same curves of Fig. 4(a) . The inset emphasizes the role of Fabry-Pérot fringes in the pass-band.
Parameters used in the design of the single-layer, the double-layer, and the triple-layer (only simulated) filters with at 1 THz (units are μm).
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