Ultra-Broadband and Electro-Optical Tunable Absorption in Double-Walled Carbon Nanotubes

Electro-optical modulators are critical elements in the rapidly developing data communication, optical interconnects, silicon-based photonic systems and terahertz technologies. The limited optoelectronic properties and complicated material growth in traditional semiconductors hinder the rapidly surging demand for modulator performance, energy efficiency, cost, etc. The emergence of two-dimensional materials and one-dimensional carbon nanotubes in recent decades has brought new opportunities with their tremendous selection degree of freedom for exceptional optoelectronic properties. In this article, we present ultra-broadband and electro-optical tunable absorption modulators by employing double-walled carbon nanotube films in a capacitor geometry, spanning the visible to terahertz spectra. The formation of supercapacitors around the ionic gel electrolyte and carbon nanotube film interfaces accounts for the large carrier transition and optical conductivity change, which behaves a thickness dependent electroabsorption dynamics. Our findings not only broaden the understanding of low-dimensional material applications in electro-optics but also pave the way for future developments in high-performance broadband modulators.