Abstract
For easy manipulation of polarization states of light for applications in communications, imaging, and information processing, an efficient mechanism is desired for rotating light polarization with a minimum interaction length. Here, we report giant polarization rotations for terahertz (THz) electromagnetic waves in ultrathin ( ∼ 45 n m ), high-density films of aligned carbon nanotubes. We observed polarization rotations of up to ∼ 20 ∘ and ∼ 110 ∘ for transmitted and reflected THz pulses, respectively. The amount of polarization rotation was a sensitive function of the angle between the incident THz polarization and the nanotube alignment direction, exhibiting a “magic” angle at which the total rotation through transmission and reflection becomes exactly 90°. Our model quantitatively explains these giant rotations as a result of extremely anisotropic optical constants, demonstrating that aligned carbon nanotubes promise ultrathin, broadband, and tunable THz polarization devices.
Highlights
Recent studies have focused on exploiting metamaterials, which enable efficient polarization rotation and conversion of THz waves [9,10] with a large bandwidth [11,12], but their fabrication is typically realized based on expensive methodologies
We demonstrate that the observed giant polarization rotations are a result of the extremely anisotropic optical constants of the carbon nanotubes (CNTs) films, and that the magic angle can be tuned by changing the substrate refractive index and the film thickness
A dilute aqueous suspension of SWCNTs with sodium deoxycholate surfactant (0.01%) was filtered using a vacuum filtration system at a well-controlled speed, which resulted in a wafer-scale crystalline SWCNT film in which nanotubes are nearly perfectly aligned and maximally packed (∼1 nanotube per cross-sectional area of 1 nm2)
Summary
Terahertz (THz) technology has made impressive advances in the last decade, finding a wide variety of applications in spectroscopy, imaging, sensing, and communications [1]. Basic components such as polarizers, waveplates, and filters are still limited for THz optics. The widely used THz polarizers are wire-grid polarizers [2], which are fragile, inflexible, and non-adjustable; they require precise fabrication procedures and have low extinction ratios compared to polarizers available in the infrared or visible spectral range [3]. To further advance various THz applications, robust material platforms as well as new implementable polarization control schemes are desired. Realizing accessible THz technologies requires developing robust and implementable polarization control for this spectral region. Recent studies have focused on exploiting metamaterials, which enable efficient polarization rotation and conversion of THz waves [9,10] with a large bandwidth [11,12], but their fabrication is typically realized based on expensive methodologies
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