Fig. 1. Procedure of sample preparation

Fig. 2. Micrographs of samples. (a) Micrograph of sample 1 with discontinuous reinforced lines; (b) micrograph of sample 2 with continuous reinforced lines; (c) micrograph of commercial WGP. Insets in Figs. 2(a) and 2(b) show WGP designs

Fig. 3. Transmittance for different samples varying with angle θ between polarization direction of incident THz wave and line grating simulated by FDTD. (a) Without reinforced lines; (b) with discontinuous reinforced lines; (c) with continuous reinforced lines

Fig. 4. Measured THz spectra of samples at different θ. (a) Sample 1; (b) sample 3

Fig. 5. Simulated transmittance of samples at different θ. (a) Sample 1; (b) sample 3

Fig. 6. Degree of polarization (R_Dop) and extinction ratio (R_er) of samples 1 and 3. (a) Degree of polarization; (b) extinction ratio