Ultrafast opto-mechanical terahertz modulators based on stretchable carbon nanotube thin films

TL;DR

This paper presents a novel ultrafast, stretchable opto-mechanical terahertz modulator using carbon nanotube thin films, achieving high modulation depths and tunability through mechanical strain, with potential applications in high-speed THz devices.

Contribution

It introduces a new type of stretchable THz modulator based on SWCNT films, demonstrating tunable modulation depth via mechanical strain and polarization sensitivity.

Findings

Achieved 100% modulation depth without strain and 65% at 40% strain.

Demonstrated 3-4 orders of magnitude change in photoconductivity.

Showed polarization sensitivity useful for stretchable polarizer design.

Abstract

For terahertz (THz) wave applications, tunable and rapid modulation is highly required. When studied by means of optical pump-terahertz probe spectroscopy, single-walled carbon nanotubes (SWCNTs) thin films demonstrated ultrafast carrier recombination lifetimes with a high relative change in the signal under optical excitation, making them promising candidates for high-speed modulators. Here, combination of SWCNTthin films and stretchable substrates facilitated studies of the SWCNT mechanical properties under strain,and enabled the development of a new type of an opto-mechanical modulator. By applying a certain strain to the SWCNT films, the effective sheet conductance and therefore modulation depth can be fine-tuned to optimize the designed modulator. Modulators exhibited a photoconductivity change of 3-4 orders of magnitude under the strain due to the structural modification in the SWCNT network. Stretching was used to control the THz signal with a modulation depth of around 100 % without strain and 65 % at a high strainoperation of 40 %. The sensitivity of modulators to beam polarisation is also shown, which might also come in handy for the design of a stretchable polariser. Our results give a fundamental grounding for the design of high-sensitivity stretchable devices based on SWCNT films.