CNT-THz polarizer


Utilizing highly oriented multiwalled carbon nanotube aerogel sheets, we fabricated micrometer-thick freestanding carbon nanotube (CNT) polarizers. Simple winding of nanotube sheets on a U-shaped polyethylene reel enabled rapid and reliable polarizer fabrication, bypassing lithography or chemical etching processes. With the remarkable extinction ratio reaching ∼37 dB in the broad spectral range from 0.1 to 2.0 THz, combined with the extraordinary gravimetric mechanical strength of CNTs, and the dispersionless character of freestanding sheets, the commercialization prospects for our CNT terahertz polarizers appear attractive.

Figure 1. (a) Schematic diagram for the fabrication of a freestanding CNT polarizer using U-shaped PE (polyethylene) frame and highly aligned CNT sheet, drawn from a sidewall of a MWCNT forest. When the PE reel is rotated once, two layers of the CNT sheets are stacked. (b) Photographic and (c)SEM images of our 75-layer CNT sheet polarizer.


Figure 2. (a) Experimental scheme for the polarization state measurements. The incident THz beam is polarized along the x-axis and the CNT sheet polarizer was rotated from θ = 0 to 360in 15 interval. The 75-layer CNT sheet is used as a polarizer and 0 (90) corresponds to the nanotube orientation direction being perpendicular (parallel) to the polarization of the incident THz waves. (b) Time traces for x-component (Ex) electric fields for the different polarizer angles (0, 45, and 90). The reference signal (gray line) is measured without any CNT polarizer. More than 2 orders of magnitude extinction are observed between the perpendicular (0) and parallel (90) orientation.

Figure 3. Comparison between the performances of a commercial freestanding wire-grid polarizer and the 75-layer freestanding CNT sheet polarizer. (a) The ratios of the minimum and the maximum transmission (Tmin/Tmax) and  (b) Transmission spectra for various polarizer angles from θ = 0 to 90 degree. The transmission signals are normalized to the reference signal (without a CNT sheet polarizer). Averaged between 0.1 to 2.0 THz, over 50% transmission is shown for 0, while only 10^-4 transmission is observed at 90 degree.



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