Double-walled carbon nanotube film as the active electrode in an electro-optical modulator for the mid-infrared and terahertz regions

The lack of efficient optical components operating with terahertz (THz) radiation is a limiting step in the ongoing large-scale development of this technology in fields such as telecommunication and imaging. In this work, we propose the use of double-walled carbon nanotube (DWCNT) films as the active electrode in THz modulation devices. Using six bounces in an internal total reflection configuration in a silicon waveguide prism, we achieved high attenuation from a 5 nm thin film, reaching up to - Delta T / T = 6% at 50 THz, albeit with a slow speed of modulation on the order of minutes. Moreover, this attenuation - Delta T / T attains a value of 20% at 30 THz using a thicker 20 nm DWCNT film. As a consequence of doping, the modulation of a phonon-related Fano resonance is also observed in the mid-infrared, which could be used as a modulable narrow-band optoelectronic filter. Our study provides a sense of the capabilities unlocked by exploiting the optical and electronic properties of carbon nanotubes in the terahertz and infrared regimes.